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The retention of magnetic fields in rotating terrestrial objects through the actions of a close large orbital partner

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The retention of magnetic fields in rotating terrestrial objects through the actions of a close large orbital partner
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Swartz, Kenneth Neil
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English
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xi, 87 leaves : illustrations ; 28 cm

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Magnetic fields ( lcsh )
Geomagnetism ( lcsh )
Dynamo theory (Cosmic physics) ( lcsh )
Dynamo theory (Cosmic physics) ( fast )
Geomagnetism ( fast )
Magnetic fields ( fast )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Bibliography:
Includes bibliographical references (leaves 84-87).
Statement of Responsibility:
by Kenneth Neil Swartz.

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|University of Colorado Denver
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|Auraria Library
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ocm42612653
Classification:
LD1190.L44 1999m .S83 ( lcc )

Full Text
THE RETENTION OF MAGNETIC FIELDS IN ROTATING
TERRESTRIAL OBJECTS THROUGH THE ACTIONS
OF A CLOSE LARGE ORBITAL PARTNER
by
Kenneth Neil Swartz
A thesis submitted to the
University of Colorado at Denver
in partial fufillment
of the requirements for the degree of
Master of Basic Science
1999


This thesis for the Master of Basic Science
degree by
Kenneth Neil Swartz
has been approved
by
Steve Doty

Date


Swartz, Kenneth Neil (M.B.S.)
The Retention of Magnetic Fields in Rotating Terrestrial
Objects Through the Actions of a Close Large Orbital
Partner
Thesis directed by Professor John Weihaupt and Associate
Professor Steve Doty
ABSTRACT
The source of internally generated magnetic fields
in terrestrial objects remains unknown. Numerous
theories have been postulated to understand the
generation of internal magnetic fields and most hold
they are formed by currents in the predominately iron
molten outer core of these terrestrial objects. These
currents are thought to produce the magnetic field
through a self-exciting dynamo process and are driven
by the transfer of internal heat towards the surface
of the terrestrial object through convection.
A comprehensive theory on the structure of these
convective currents and the sources of heat driving
them, remains to be developed. This is especially true
for the terrestrial bodies of Mercury and Ganymede.
Though quite different from the Earth, they are known
to possess significant internally generated magnetic
111


fields. Most theories which have been postulated to
explain the Earth's magnetic field are incapable of
explaining the generation of magnetic fields in
these smaller terrestrial objects.
The missing part of a theory that better explains
internally generated magnetic fields is an adequate
explanation as to the source of heat needed to retain
the internal dynamo into the present era. Most theories
hold these terrestrial objects became magma oceans soon
after their formation and this original heat, along
with heat generated later through internal
differentiation, core crystallization and radioactive
decay, continues to drive the self-exciting dynamo of
the outer core. This paper will attempt to show by
a comparison among the terrestrial objects that the
currently postulated sources of heat are inadequate
to explain the retention of an internally generated
magnetic field in a terrestrial object.
In contrast to traditional hypotheses, this paper
postulates that gravitational distortions produced by
a close large orbital partner (CLOP) on the inner core
of a rotating terrestrial object encased in a molten
outer core can help explain the continued retention
of an internally generated magnetic field. The CLOP
process causes a transfer of angular momentum from the
planet to its inner core. This angular momentum is
dissipated through the formation of currents and
friction at the inner core/outer core boundary,
driving the geomagnetic dynamo.
IV


This abstract accurately represents the content of
the candidate's thesis. I recommend its publication.
v


ACKNOWLEDGMENTS
I am most grateful to Prof. Jack Weihaupt, chair
of my committee, for his guidance and support during
my study at the university and in the preparation of
the paper. Specifically, I thank him for reviewing
this paper's several preliminary versions suggesting
modification to improve the final copy. His expertise,
experience and efforts to keep me focused on the
important aspects of this paper is much appreciated.
My special thanks goes to Assistant Prof. Steve
Doty. His understanding and research of planetary system
physics was most helpful, especially in the mathematical
constructs showing the potential and limitations of
the theory.
I thank also the third member of my committee,
Prof. Clyde Zaidins, for serving in his capacity on
the committee and for his encouragement and interest
in the concept.


CONTENTS
Tables...............................................ix
Figures..............................................x
Equations...........................................xi
Chapter
1. Introduction.......................'............1
1.1 Planetary Magnetic Fields........................1
1.2 Terrestrial Bodies With Magnetic Fields..........2
1.3 Purpose and Scope................................4
2. Geologic History of Terrestrial Planets..........5
2.1 Formation of the Terrestrial Planets.............5
2.2 The Magma Ocean..................................9
2.3 Heat Budget of the Earth........................11
3. The Terrestrial Planets.........................18
3.1 Purpose of Comparisons..........................18
3.2 Mercury.........................................19
3.3 Mars.......................................... 23
3.4 Earth/Moon System...............................27
3.5 Venus......................................... 36
4. Close Large Orbital Partner Hypothesis..........41
4.1 Close Large Orbital Partner (CLOP) Process......41
4.2 Tidal Torque....................................44
vii


4.3 The CLOP Process...............................4 5
4.4 Differential Core Rotation......................49
4.5 CLOP Efficiency.................................53
4.6 Evolution of a Terrestrial Planet...............57
5. The Galilean Satellites.........................61
5.1 The Gallilean Satellites........................61
5.2 Io..............................................64
5.3 Magneto-Convection..............................67
5.4 Europa..........................................68
5.5 Ganymede........................................69
5.6 Callisto........................................73
5.7 Orbital Dynamics of the Galilean Satellites....76
5.8 CLOP Interaction in a Laplace Orbital System...78
Conclusion..........................................82
References..........................................84
viii


TABLES
Table
2.1 Stability Fields of Equalibrium Conden.........8
2.2 Average Radiogenic Heat in Geo. Material......10
2.3 Heat Budget of the Earth......................12
3.3 Phy. Characteristics of the Inner Planets.... 28
3.4 Parameters for the Earth's Core...............34
3.4 Estimates of Properties of the Earth's Core..34
5.2 Basic Properties of the Galilean Satellites..63
IX


FIGURES
Figures
2.3 Thermal History of Mantle & Core............15
4.1 Lunar Asymmetry..............................43
4.3 Clop Distortions........................... 48
4.3 Tidal Differences.......................... 48
4.4 Coil Currents................................50
4.5 Earth's Rotational History................. 55
5.8 Galilean System Dynamics.....................79
x


EQUATIONS
Equation
4.4 Efficiency of Earth/Moon CLOP
4.4 Approximate Efficiency of Mercury/Sun CLOP.
56
.58
xi


1. Introduction
1.1 Planetary Magnetic Fields
Planetary magnetic fields are quite common in our
solar system. The gas giants of Jupiter, Saturn, Uranus,
and Neptune all have substantial magnetic fields. These
magnetic fields are thought to be generated in a manner
somewhat similar to that of the Sun's. Common features
of these bodies is their gaseous composition, large
size, the radiation of significantly more energy than
they receive, and dense cores that are thought to rotate
more rapidly than their surfaces.
Of the four terrestrial planets, only the Earth
and Mercury are known to currently possess significant
magnetic fields, which are thought to be produced by
a dynamo process in their predominately iron molten
outer cores. In the past, Mars may also have possessed
a significant magnetic field, if the measurements of
fossil magnetic fields obtained from Mars orbiting
spacecraft are correct (Acuna 1998). If Venus once
possessed a magnetic field is not known, and further
space exploration is needed to examine this possibility.
At least one moon in the solar system also possesses
a magnetic field. Ganymede, the third Galilean satellite
of Jupiter, has a magnetic field at about the strength
of Mercury's. Moons possessing magnetic fields do not
appear to be unique, as rock samples gathered by the
Apollo program indicate the Earth's Moon at one time
also possessed a significant magnetic field (Murray


1981). Some theorize the Galilean satellites of Io
and Europa may have had magnetic fields at times in
their orbital histories. Whether other large moons
of Saturn, Uranus, Neptune and Pluto possess significant
or fossil magnetic fields remains to be discovered.
1.2 Terrestrial Bodies with
Magnetic Fields
The three terrestrial bodies in the solar system
.which are known to possess magnetic fields Mercury,
Earth and Ganymede, have two potentially important
features in common. All rotate relative to a close
large orbital partner. In the case of Mercury, it is
the Sun; for the Earth it is the Moon; and for Ganymede
it is Jupiter and the other Galilean satellites. Venus,
Mars and the Moon lack at least one of these features
and none currently possesses a significant magnetic
field.
Mercury presently has a magnetic field with a
strength of around 1% that of the Earth's (Murray 1981).
Ganymede's magnetic field is around 1.4% (Kivelson 1996),
as compared to the Earth. The presence of these magnetic
fields indicates it is likely these bodies have molten
metallic outer cores with substantial currents to produce
an internal dynamo, as well as solid predominately iron
inner cores. The cores of both terrestrial objects
are also encased in a ferro-magnesium silicate mantle
(Kivelson 1996).
The source of energy needed to sustain a molten
core in a body as small as Mercury or Ganymede remains
problematical, as convection and radiant cooling by
most estimates should have by now reduced the internal
2


temperature of these bodies to well below that of liquid
iron (Murray 1981). The majority of initial heat
generated during a probable molten phase early in the
bodies' history would have dissipated through radiant
cooling to below the temperature of liquid iron over
the last four and half billion years (Murray 1981).
Any heat produced during the solidification of an inner
core from a possibly liquid core and radioactive decay,
would have dispersed through convection and radiant
cooling in these relatively small bodies (Murray 1981).
The current internal temperatures of Mercury and
Ganymede are still thought to remain above the Curie
point (500 C). Temperatures above the Curie point
suppress the formation of permanent magnetic fields
in ferric compounds, preventing the retention of an
internal fossil magnetic field. Additionally, the
recent discovery of pressure constraints on magnetic
fields in ferrous substances at pressures similar to
the interiors of these bodies, nearly ensures that a
fossil magnetic field is not a possible cause of the
magnetic fields of Mercury and Ganymede (Cohen 1997).
It is important to note that the source of energy
for the CLOP hypothesis arises from the transfer of
angular momentum from the rotating planet to its inner
core. The deposition of this energy occurs predominately
in the inner core and is expressed on the inner
core/outer core surface boundary as friction. The CLOP
process is likely a relatively weak transfer of energy.
In the case of Mercury and Ganymede, the CLOP process
is strong enough to generate a magnetic field at around
1% that of the Earth's, but appears incapable of
modifying the surfaces of these bodies through tectonic
3


or volcanic processes, as both objects appear to have
no internally generated surface activity for over a
billion years. (Murray 1981).
1.3 Purpose and Scope of this Paper
The mystery of magnetic field generation in the
relatively small and geological inactive terrestrial
bodies of Mercury and Ganymede was the impetus behind
the formation of the CLOP hypothesis. Unfortunately
the geological information gathered on most terrestrial
bodies is limited, so the better understood geology
of the Earth must serve as the basis for the modeling
of the internal dynamics of these terrestrial objects.
As orbital relationships are critical for the hypothesis,
associated patterns need to be investigated. The first
topic examined will be the formation and history of
terrestrial objects.
As both planets and moons will be examined in the
paper, these bodies will be referred to as terrestrial
objects. A terrestrial object is defined as a
substantial solar system body with a metallic core
encased in a silicate mantle which may be covered by
liquid water or ice.
4


2. Geological History of the
Terrestrial Planets
2.1 Formation of the Terrestrial Planets
The formation of the terrestrial planets is an
important factor to examine, as the composition and
internal structure of a planet will determine if a CLOP
process is possible. The location of a planet's
formation in the early nebula has implications for its
size, chemical composition and orbital harmonics.
Several patterns are evident in the current structure
of the solar system and reflect the effects of various
forces acting on the early nebula during planetary
formation. Therefore, an examination of the processes
of terrestrial planet formation is needed before the
planets themselves, or the mechanisms of convection
and core dynamics can be evaluated. Due to our limited
understanding of the terrestrial planets, the Earth
will again be the main source of information in this
process.
It was once believed the inner planets were
homogeneously accreted in a cold state. The dust grains
of the early nebula slowly accreted into ever larger
bodies to form the inner planets. The early Earth was
seen to be much like Jupiter, with a heavy primary
atmosphere. Later, heat from the decay of radioactive
elements turned the interiors of these planets molten
and the Sun's violent ignition blasted away the primary
atmosphere.
5


The iron rich substances within these bodies sank
to form the core, while silicates rose to form the mantle
and crust (Murray 1981). This process of differentiation
and solidification generated considerable heat through
density driven currents and the heat of fusion. The
largest source of heat after this differentiation event
was believed to be produced by residual radioactivity
in the planetary interior. The heat of differentiation
and radioactive decay were believed to be the primary
sources of energy generating the magnetic field of
the Earth.
Information gained from space exploration and
improved scientific data indicates a hot heterogeneous
accretion for the inner planets is a more likely
scenario. The area of the nebula from which the inner
planets first formed became extremely hot due to the
violence of early solar nuclear ignition.
Electromagnetic radiation and solar ions vaporized the
cosmic dust particles and drove off the gases of hydrogen
and helium, as well as light volatile compounds such
as methane, water, carbon dioxide and ammonia from the
area of inner planet formation. This early chemical
differentiation in the nebula is also thought to be
responsible for the ratios of iron to silicates in the
inner planets.
As nebula temperatures later fell, condensation
of the remaining compounds began. First aluminum oxides
would condense, followed by iron/nickel and later
silicate compounds. The size of the original condensate
bodies of the different compounds, the processes by
which they formed larger bodies and eventually formed
planets, are still speculative.
6


There are two main scientific scenarios on the
condensation of the inner planets. Table 1, notes the
various compounds thought to be present in the nebula.
The rate of cooling of the nebula from which the inner
planets formed is critical to which scenario is the
most likely.
In the simplest scenario the nebula cools quickly
and the bodies that form are homogeneous. An examination
of the mesosiderite asteroids believed to have formed
by this processes is useful. Our knowledge of the
mesosiderite asteroids is obtained from meteorites thrown
off in later highly destructive collisions of these
asteroids, and can give a good approximation of how
long it took these protoplanets to differentiate.
Mesosiderite asteroids are thought to have been around
100 km in diameter and formed approximately 4.56
Gigayears ago (Rubin 1997). Isotopic studies indicate
they had chemically differentiated by 4.48 Gigayears,
less than 100 million years after formation (Rubin 1997).
Radioactivity of extinct isotopes is thought to
be the main cause of their differentiation.
These
.... 26, - 60^ 107 , 1 29t 146e 236rT and 244D
nuclides Al, Fe, Pd, I, Sm, U, Pu,
were quite intense, but short lived radioactive isotopes
(Stacy 1992), and formed in the supernova which may
have contributed to and caused the collapse of the
presolar nebula to form the solar system.
In the other scenario, the protoplanets formed
heterogeneously with a small aluminum/calcium oxide
central cores, which then were quickly covered with
iron/nickel compounds. Some hypothesize the magnetic
properties of iron nickel particles may have aided in
this accretion process. The last compounds to condense


TABLE 1
STABILIY FIELDS OF EQUALIBRIUM CONDENSATES
AT 10"3 ATMOSPHERES
Condensation Temperature of
Phase_________________temperature (K) disappearance(K)
Corundum Al23 1 758 1 51 3
Perovskite CaTi03 1 647 1393
Melilite Ca2Al2Si07 1 625 1 450
Spinel MgAl204 1 51 3 1 362
Metalic Iron (Fi, Ni) 1 473
Diopside CaMgSi204 1 450
Forsterite Mg SiO 1 444
Ti305 1 393 11 25
Anorthite CaAl2Si2Og 1 362
Enstatite MgSiOg 1 349
Eskolaite Cr23 1 294
Metalic Cobalt Co 1 274
Alabandite MnS 1 1 39
Rutile Ti02 11 25
Alkali Feldspa r (Na, K)*
AlSi308 1 000
Troilite FeS 700
Magnetite Fe34 405
Ice h2o 200
*_
40
K major radioactive element
(after Jacobs 1987)
8


were the various silicate oxide compounds, which later
formed the mantle and crust.
2 6
Due to the Al produced in the supernova which
may have caused the collapse of the nebula, any initial
significant aluminum oxide based body would have become
rapidly molten and any iron/nickel compounds it contained
would quickly sink to form a dense core, along with
any iron/nickel bodies it accreted at this time. This
early radioactive heat, along with the heat generated
by the accretion of the large amounts of later silicates,
would help keep the planet entirely molten (Jacobs 1987).
2.2 The Magma Ocean
In either scenario, these early protoplanets are
thought to have become entirely molten during or soon
after formation due to the heat of radioactive isotopes
and a constant rain of meteoric bodies. In this
planetary magma ocean, chemical differentiation would
have been active, adding even more heat to sustain the
magma ocean. Additionally, density differences would
have kept any later acquired lighter compounds floating
near the surfaces of these bodies.
This early molten state helps eliminate radioactive
substances as being the main source of heat within the
cores of the Earth or the other terrestrial planets.
The present, naturally occurring radioactive isotopes
of uranium, thorium and potassium tend to form chemically
stable and relatively light complex oxides, and
silicates. These compounds besides being the last to
condense from the nebula, would tend rise to the top
of the magma ocean. In Table 2, it can be clearly
observed most of these radioactive minerals are today
9


TABLE 2 AVERAGE RADIOGENIC HEAT IN GEOLOGICAL MATERIALS
Material Concentration (ppm.) Heat
Production
U TH K K/U (10 W/kg)
Igneous Rocks
granites 4.6 18 33,000 7,000 1 050
alkali basalts 0.75 2.5 12,000 16,000 80
theoletic basalts 0.11 0.4 1 ,500 13,600 27
eclogites 0.035 0.15 500 14,000 9.2
peridontities, dunites 0.006 0.02 1 00 17,000 1 .5
Meteorites
carbonaceous chondrites 0.02
ordinary chondrites 0.015
iron meteorites nil
Moon
Apollo samples 0.23
Global Averages
crust (2.8 x 1022 kg) 1.2
mantle (4.0 x 10^ kg) 0.025
core nil
whole earth 0.022
0.07 400 20,000 5.2
0.046 900 60,000 5.8
nil nil 3e-4
0.85 590 2,500 47.0
4.5 15,500 13,000 293.0
0.087 70 2,800 5.1
nil nil nil
0.079 1 1 9 5,400 4.7
(after Stacy 1992)
10


found almost exclusively in the aluminum silicate
continental crust of the Earth (Stacy 1992).
A far lesser amount of radioactive elements
(primarily potassium 40) are contained in the basalts
and other associated compounds. The source of basalts,
especially oceanic basalts is thought to be the partially
molten asthenosphere upon which the lithosphere rides.
The molten upper part of the asthenosphere changes to
a more solid state at around 250 km. This physical
change is thought to be due to the precipitation of
spinel and formation of ringwoodit largely in turn
caused by pressure induced phase change. Periodite,
which forms at around 700 km is shown in Table 2 and
contains a tiny fraction of radioactive elements as
compared to olivine basalts (Press 1978). The separation
of potassium containing compounds and other lighter
substances may be occurring at the spinel and the
periodite formation zone, reducing the potassium levels
in the lower parts of the mantle (Press 1978).
These mineral phase changes affect the distribution
of radioactive elements and results in nearly all
radioactive elements being contained in the top 700
kilometers of the upper mantle and crust. Additionally,
as most subducted oceanic crust never goes below this
700 km depth which defines the base of the upper mantle,
this further limits the distribution of radioactive
elements.
2.3 Heat Budget of the Earth
The concentration of radioactive compounds in the
upper mantle of the Earth puts constraints on the
possible sources of internal planetary heat. The heat
11


Table 3
THE HEAT BUDGET OF THE EARTH
1 2
(all values in units of 10 Watts)
INCOME
Crustal radioactivity 8.2
Mantle radioactivity 19.9 25?
Latent heat and gravitational energy
released by core evolution 1.2
Gravitational energy of mantle
differentiation 0.6
Gravitational energy released
by thermal contraction 2.1
Total ______
32.0 37.1?
EXPENDITURE
Crustal heat loss 8.2
Mantle heat loss 30.8
Core heat loss 3.0
Total
42.0
Net loss of heat 10.0
(after Stacy 1992)
12


budget in the chart is a good consolidation of what
is known about internal heat sources and losses of the
Earth (Stacy 1992). It should be noted this budget
uses 2800 ppm of K in the mantle, though levels of 1500
ppm are more likely (Stacy 1992). In any case, the
level of accuracy of the data is quite uncertain.
An important factor to note in Table 2 is the
global averages of potassium the whole Earth as compared
to the potassium level of the Meteorites. If chondrites
are the main source of silicates in the mantle, a
significant amount of Earth potassium is missing.
One argument given for this difference, is the area'
of the nebula from which the Earth formed was lower
in potassium compound concentrations.
The main heat effect of radioactivity is found
in the mantle and crust. Crustal radioactivity
contributes little to internal convection and most
radioactive substances appear to occur in the upper
mantle limiting their contribution to convection.
The amount of heat in the mantle may also be
overestimated if the 1500 ppm K is closer to actual
mantle concentrations than the estimated 2800 ppm K
for the heat budget. In this case, 1500 ppm/ 2800 ppm
becomes 10.7/ 19.9 terawatts fpr mantle heat budget
radioactivity.
This heat budget also does not take into account
heat losses by plume and hot spot activity on the Earth.
This limitation may be partially offset by the relatively
recent seismic data which indicates some subducting
oceanic plates sink all the way down to the core-mantle
boundary (CMB). These deep subducting oceanic plates
are the oldest and coldest of the oceanic plates and
13


bring with them higher basaltic potassium concentrations.
These subducted plates appear responsible for the uneven
topography of the CMB and their melt likely forms the
intermittent melt layer at the base of the Earth's mantle
(Williams 1996). This melt is thought to be the main
source of material supplying the numerous hot spots
on the Earth.
From this information on the heat budget a graph
was derived, Figure 1, which contains additional
information showing core and mantle heat changes over
the history of the Earth. The important data are the
two solid Tg lines. The upper line n = 3 is based on
the heat budget figures as currently understood, but
the rheology (crustal subduction speeds) is
non-Newtonian.
A Newtonian rheology refers to the- presently
observed speed of oceanic crustal plates subduction
appearing to be approximately proportional to the square
root at the age of subduction (Stacy 1992). In simpler
terms, if the age of the oceanic plate being subducted
is doubled, the subduction speed of the plate increases
fourfold. This is one explanation why only the oldest
oceanic plates can penetrate the lower mantle.
Non-Newtonian rheology in Figure 1 is oceanic crust
subduction rates being less than the above model
description with respect to crustal age. A non-Newtonian
rheology is illustrated in line n = 1 of Figure 1 and
is based on the rate of crustal subduction on the Earth
as currently understood.
If actual observed subduction speeds are used to
extrapolate the Earth's heat history, this would create
linear rheology and is shown as the Tg slope of n=3.
14


Figure 1. Internal Heat of the Earth Over Geologic Time
4iMK>
V
m
* \
\ \
v-V
\ i = 3 fQw 10,9 x 10,SW)
\ ''v
v. \
n 1 ">>. "
<0^^251 x10,2Wi
3800
3KW!
T(K)
3'KXJ
- 32GO
^ * 1 ; jh Time Pfwstnl {10* years!
Note: Mantle cooling relative to core cooling over geologic time
3000
tn


This would require a mantle radioactivity of 25 terawatts
indicating 5.1 terawatts of power must be added by some
other mechanism not illustrated in the heat budget
(Stacy 1992).
This scenario would make the income of latent heat
and gravitational energy released by core evolution
even more important, as they are the only generally
accepted sources of core heat. From Figure 1, it can
be seen the core has remained at nearly the same
temperature (Tc), while the mantle temperature has
dropped significantly. This temperature data gained
from seismic studies and seems to indicate a substantial
heat source is located in the core itself and that the
core is an increasingly significant factor in mantle
convection.
In the heat budget of Table 3, gravitational energy
refers to both the solidification of the inner core
from the liquid outer core (heat of fusion) and possibly
lighter molten fractional material (FeS or FeO) rising
from the inner core to the CMB (density driven
gravitational energy), as well as latent heat within
the core. Unfortunately, the heat budget does not
separate these processes to give a better understanding
of the heat budget.
If core heat was supplied by the simple freezing
of the inner core, the entire core would freeze solid
in a few hundred million years (Stacy 1992). This
process along with density currents from eutectic richer
residue at the freeze zone, are held as the main energy
sources to generate currents in the outer core. As
a significant fraction the missing +5 terawatts appears
to be generated in the core, these processes are either
16


underestimated, which is unlikely or some unknown process
is generating the needed core heat.
Unaccounted for heat sources are also evident in
some of the other terrestrial objects. Mercury and
Ganymede have an excess of heat than can be accounted
for by current planetary theory, as reflected in their
dynamo generated magnetic fields. While Venus seems
to have a lack of excess heat, as compared to its near
twin the Earth. The CLOP hypothesis can help account
for some of this missing heat, especially that needed
for the core of the Earth. It is at this point the
inner planets need to be examined in greater detail.
17


3. The Terrestrial Planets
3.1 Purpose of Comparison
In examining the dynamics of the magnetic fields
of terrestrial objects, one is faced with the limitations
of only a few examples. As mentioned before, it appears
likely all the terrestrial objects at one time possessed
magnetic fields. At the present, only Mercury, Earth
and the Galilean satellite Ganymede are known to possess
internally generated magnetic fields. Another Galilean
satellite Io, may also possess an internally generated
magnetic field.
The most likely cause for this difference appears
to be the decrease of internal heat over time, until
it is below a level needed to drive the self exciting
dynamo which generates the magnetic field. Yet the
question remains as to why such similar bodies as the
Earth and Venus, or to some extent Mercury and Mars
are so different in this regard.
The hypothesis of this paper suggests the retention
of a planetary magnetic field as dependent on both the
rotation rate of the planet and the presence of a close
large orbital partner. This chapter will compare and
contrast, first Mercury and Mars, as understanding the
source of Mercury's magnetic field is important to
putting constraints on energy production of the CLOP
process. The Earth and Venus will also be compared
and contrasted with special emphasis on the core
18


dynamics of the Earth before the CLOP hypothesis is
examined in detail.
3.1 Mercury
The most inner planet Mercury is a planet of harsh
extremes. At only .387 AU from the Sun, solar radiation
intensities at its surface range from 5 to 10 times
that of the Earth. This results in daytime temperatures
up to 430C and due to the lack of an atmosphere,
temperatures -180C at night (Murray 1981), giving
Mercury the greatest extremes in surface temperature
of any body in the solar system. The surface temperature
of Venus at 700 C is hotter, but due to its thick carbon
dioxide atmosphere, very little diurnal variation exists.
Due to Mercury's close location to the Sun, little
was know about this planet until relatively recently,
other than its orbital period was 88 days and it had
the highest orbital eccentricity of any inner planet
at .206. At one time Mercury was thought to be like
the Earth's Moon by always keeping the same hemisphere
facing the Sun. It was only in the mid-1960s, due to
Earth based measurements, that the correct rotation
period of Mercury of 58.65 Earth days became known.
Mercury has unique orbital harmonics, as its day
and orbital period are locked in pattern called
spin-orbital coupling. For every two times Mercury
orbits the Sun, it rotates on its axis precisely three
times. This 2/3 spin orbital coupling along with its
high eccentricity gives Mercury a most interesting
pattern of surface heating. The longitudes of 0 and
180 face the Sun during perihelion, while the longitudes
19


90 and 270 are illuminated at aphelion, and receive
around half as much solar energy.
The high eccentricity of Mercury is likely also
to affect its internal dynamics through tidal heating,
due to the strong gravity field of the Sun. The
intensity of potential tidal heating is measured as
the square of the orbital eccentricity (always less
than one), but then is modified inversely as a large
power of the orbital frequency.
Mercury is in the highest gravitation environment
of any planet due to its orbital location near the sun.
This results in the shortest orbital period of any
planet, and along with the highest eccentricity of any
inner planet creates by far the greatest potential for
tidal heating of any planet. In the scientific
literature there seems to be little examination of
this potential heat source.
The high eccentricity of Mercury is unusual given
its orbital environment. Most orbiting bodies which
are undergoing a transfer of energy from their orbital
partner have achieved nearly circular orbits over solar
system history. The Earth/Moon system, Venus, the
Galilean satellites and most other large moons of the
outer planets are some examples. Tidal flexing in a
high gravitational environment as Mercury experiences,
is efficient at damping eccentricity. Mercury is also
experiencing the transfer of angular momentum from the
Sun due to tidal torque. This process also has the
net effect of reducing eccentricity.
Several possibilities as to the cause and retention
of Mercury's high eccentricity can be hypothesized.
The first and most unlikely is a close encounter of
20


Mercury by a large body. A second possibility is the
present eccentricity is only a remnant of an even greater
past eccentricity. This possibility is also unlikely
from our understanding of terrestrial planet formation,
as well as the reduction of such a high eccentricity
would have generated considerable heat and perhaps caused
tectonic or volcanic surface modification. A unusual
possibility is the 2/3 orbital harmonic of Mercury which
is somehow pumping up the eccentricity. This unusual
type of orbital swinging would have to be substantial
enough to counteract loses of eccentricity due to tidal
flexing and tidal torque.
Mercury also has the highest uncompressed density
3
of any planets at 5.3 g/cm as compared the next highest
3
of 4.0 g/cm for the Earth (Xu 1993). Uncompressed
density refers to theoretical density if all the object's
material was at Earth surface pressures. The other
terrestrial planets of Venus, Earth, Moon, and Mars
have a fairly linear relationship between size and
density. The larger bodies of Earth and Venus are
quite dense, while the smaller bodies, Mars and the
Moon, have much lower densities. This incongruent
result may be due to Mercury's location of condensation
in the presolar nebula.
Density studies indicate the iron rich core of
Mercury is relatively large, containing nearly 80% of
its mass. This leaves only a thin silicate mantle of
640 km thick (26% of the radius) surrounding the core
(Murray 1981). This thin silicate mantle in current
planetary theory would contain nearly all the compounds
in which the radioactive elements are to be found.
The location of these elements in the thin mantle makes
21


radioactivity a most unlikely source of energy to
keep the core molten (Stacy 1992).
Mercury has around 5.5% the mass, but 38% the
surface gravity of the Earth. Its compressed density
3 3
is 5.4 g/cm versus 5.5 g/cm that of the Earth. The
orbital inclination of the ecliptic is greater than
any other terrestrial planet at 1.2, and its inclination
of the equator to the orbital plane is essentially zero.
Only one space probe has been sent to Mercury,
Mariner 10, which made three passes of Mercury on March
29. 1974, September 21, 1974 and March 16, 1975. It
is from Mariner 10 that nearly all our information on
Mercury's surface features and magnetic field was
obtained. During these flybys, it was found that Mercury
possessed a magnetic field of 600 gammas as compared
to the 50,000 gamma field of the Earth (Greeley 1994).
The surface of Mercury is heavily cratered, much like
the Moon, and shows little evidence of any internally
generated tectonic features since massive flood lavas
from around the end of accretion. The later tectonic
features that do exist consist of a few shrinkage
ridges (Murray 1981).
Whatever is the source of energy generating the
magnetic field of Mercury, it appears not to have caused
significant surface tectonic or volcanic activity.
The source of energy needed to sustain a magnetic
field in Mercury is a mystery, as the thin silicate
mantle of Mercury, where radioactive elements are
likely to be found, is far too thin to generate
sufficient heat needed to subduct or sustain a liquid
outer core and thus, a magnetic field, the same is
true of the heat generated by the crystallization
22


of the core and chemical differentiation of the
planet (Murray 1981).
Added support for this conclusion comes from
spectral analysis of Mercury surface materials. Spectral
analysis of the crustal rocks of Mercury have failed
to detect even trace amounts of iron (Nelson 1997).
In contrast, spectral analysis of the crustal rocks
of both the Mars and the Moon readily detects iron.
The lack of iron on the surface of Mercury is puzzling,
given that Mercury has the largest iron core .relative
to its size of any terrestrial object. This may indicate
that the presumed magma ocean early in Mercury's history
was internally relatively calm, allowing for a high
degree of chemical differentiation and a minimum of
thermal convection.
3.3 Mars
Mars is a relatively well studied terrestrial
planet. Numerous probes from several countries have
been sent to study its characteristics. There are even
physical samples of Martian material, as several
meteorite are believed to have come from Mars. Mars
orbits at around 1.52 AU from the Sun, has an orbital
eccentricity of only .093 and an orbital inclination
to the ecliptic of only 151'. Mars' rotational period
of 24 hours and 37 minutes and its orbital inclination
to the ecliptic of 25.2, both resemble the Earth's.
Mars is the closest terrestrial planet in size
to Mercury, with a diameter of 6787 km as compared to
4880 km for Mercury. The mass of Mars is around twice
that of Mercury's, at 10.8% versus 5.5 % the mass of
the Earth. Mars has a much lower compressed density
23


3
of 3.9 g/cm than Mercury, due to a much higher
proportion of silicates and resulting thicker mantle
(Murray 1981).
Mars like Mercury, likely was a magma ocean soon
after formation, but with proportionally a much thicker
mantle where the radioactive elements are likely to
be found and according to the radioactivity hypothesis
would generate much more heat and thus be more likely
to have retained a magnetic field than Mercury. The
same would be true of heat generated by chemical
differentiation, due to its greater mass and chemical
diversity. Yet Mars lacks a detectable magnetic field,
though there is evidence from Mars orbiting spacecraft
that Mars at one time did have a planetary magnetic
field (Acuna 1998).
The thick silicate mantle of Mars is also likely
to be responsible for a far more vigorous historic
tectonic and volcanic activity observed on the surface,
as compared to Mercury. The early tectonic activity
of Mars was similar to that of Mercury's, in that large
flood lavas covered the surface near the end of
accretion. However, unlike Mercury, martian volcanic
activity continued for a few billion more years and
is believed to be due to radioactive elements in its
mantle.
The two main areas of volcanic activity are the
Syrian and Elysium rises. These rises are several
hundred kilometers in diameter and are elevated several
kilometers over the martian mean. The gigantic shield
volcanoes of Mars are located on the surface of these
rises, and around the rises are areas of complex faulting
associated with subsurface expansion (Murray 1981).
24


Gravitational studies indicate the rises are
underlined by roots of low density material. These
areas are also thought to have once been located over
hot spots in the mantle of Mars which generated the
volcanic activity. This is good evidence for mantle
convection on Mars. Two possible reasons for this
continuing uplift have been hypothesized. One is a
plug of lighter minerals has differentiated in the
mantle and is attempting to rise to equilibrium. The
other possibility is that hot mantle currents continue
to uplift this area (Murray 1981).
Recent Satellite photo evidence from the Mars
Orbiter Camera (MOC), appears to indicate that volcanism
may have occurred on Mars in the last 40 to 100 million
years (Hartmann 1999). This conclusion was possible
due to the greater resolution of the MOC allowing for
a study of smaller crater population, to produce more
accurate dating. Only one very small spot of likely
recent volcanic activity has been observed on Mars in
the Arsia Mons caldera (Hartmann 1999). Therefore
that one of the giant volcanoes of Mars which sits
upon a major rise and has continuing volcanism, gives
credence to the concept of continuing hot mantle
currents within Mars.
Evidence tends to indicate that after the initial
flood lavas near the end of accretion, deep mantle
current or "hot spots", perhaps similar to those on
Earth, formed the rises and kept the giant volcanoes
significantly active for around a billion and a half
years after formation. As massive as these rises and
associated volcanoes are, this geological activity is
a tiny fraction of the Earth's. Mars lacks any evidence
25


of subduction or convergent zones or even significant
crustal fracturing of the kind so common on the Earth.
Not unexpectedly, there is little evidence of crustal
differentiation, except for possible mantle hot spots
continuing under the rises.
That Mars has lost its magnetic field despite its
much more vigorous tectonic history and mass than
Mercury. This indicates radioactive elements within
a terrestrial planet's mantle may not play the critical
role in the retention of a magnetic field over geologic
history as is currently thought. Although Mars rotates
with nearly the same period as the Earth it lacks a
close large orbital partner. As the CLOP hypothesis
states, both are necessary for the retention of a
magnetic field in a terrestrial object into the
present era.
26


3.4 The Earth/Moon System
The Earth is by far the most studied of all the
terrestrial planets for obvious reasons. It is from
our knowledge of the Earth, that the possible structure
and inner dynamics of the other terrestrial objects
has been derived. Therefore the convective process
inside the Earth and its internal structure needs to
be examined, especially that of the core.
Part of this examination is a determination of
the chemical composition of the core. The molten outer
core is thought composed of around 10% less dense
eutectic (easily melted) elements. The' likely eutectic
elements are sulfur and/or oxygen. In the molten outer
core they would form iron II sulfide (FeS) or iron II
oxide (FeO). A determination of which element
predominates as the less dense material of the outer
core is critical for understanding convection,
density-composition, and temperature of melting in the
outer core. An understanding of the later variable
is especially important for the small terrestrial
objects, as a significant percentage of FeS can reduce
outer core melting temperature to as low as 990 C,
in contrast to much higher melting temperatures with
FeO in the outer core (Stacy 1977).
The Earth is unique among the terrestrial planets,
in that many scientists consider the Earth/Moon system
to be a double terrestrial planetary system. Although
the Moon is only 1.3% the mass of the Earth, its diameter
is nearly a third of the Earth's. The two bodies are
27


Table 4
Physical Characteristics of the Inner Rocky Planets
MERCURY VENUS EARTH/ MOON MARS
Average Distance from Sun in AUs 0.387 0.723 1 .0 1 .524
Period of Orbit Around the Sun in Days. 88 224.7 365 687
Period of Rotation. 56d14h -243d 23h56m 24h37m
Mass Ratio of the Planet to the Earth. 0.055 0.88 1 .0 .0.013 0.1 08
Density of Planet Grams/cm2. Water=1 5.4 5.2 5.5 3.34 3.9
Equatorial Diameter in km. 4880 12,104 12,756 3,476 6787
Orbital Eccentricity. 0.2056 0.0065 0.0167 0.0933
Orbital Inclination to the Ecliptic 7.2' 323.61 (0)* 1 51 '
Inclination of Equator to Orbital Plane. 0 2.2 23.5 6.6 25.2
Mass of Moons to Planet. 0.0 0.0 0.01 3 1.0X10-
28


separated by an average distance of 384,400 km and orbit
each other every 27.32 days. Because of the mass
differences between these bodies, the barycenter of
their orbit is located around 1,100 km inside the Earth.
The orbit of the Moon around the Earth has a small
eccentricity of .055 and the orbit is tilted 6411 to
the orbit of the Earth around the Sun. The orbit of
the Earth around the Sun has a eccentricity of .017
and its orbital path defines the ecliptic plane. The
axis of the Earth is tilted 23.5 to the ecliptic and
rotates once nearly every 24 hours.
The compressed density of the Earth is the highest
3
of any terrestrial planet at 5.5 g/cm while the Moon's
3
is the least at 3.34 g/cm (Murray 1981). This great
difference is believed due to the nature of the formation
of the Earth/Moon system. The general scientific
consensus is the Earth/Moon system was created by a
collision between a proto-earth and a planetoid around
the size of Mars. The core of the colliding body and
most of its mass formed the Earth, while much of the
fragments thrown out into space coalesced to form the
Moon. The complete absence of volatile elements within
moonrocks tends to support this theory (Murray 1981).
As no direct measurements can be made of any of
the Earth's internal physical properties, seismic and
experimental data must be relied upon to determine its
inner structure. Seismic studies are giving an
increasingly more distinct view of the Earth's internal
structure. Recent technological spinoffs from hospital
ultrasound technologies applied to seismic data have
allowed the mantle convecting within the Earth to be
observed, a topographically varied core mantle boundary,
29


and the interesting feature of the inner core of the
Earth rotating faster than the rest of the planet.
The surface of the Earth is divided into two main
chemically distinct types of crust, continental crust
and oceanic crust. The continental crust is generally
higher in elevation and covers roughly 35% the surface
of the planet. The continental crust is composed
primarily of aluminum silicates and carbonate minerals.
Continental crust is too light to subduct and remains
at the surface of the planet. Continental crust is
also much thicker on average (40 km) than oceanic
crust, reaching up to 70 km thick.
The oceanic crust consists of primarily ferro-
magnesium silicates and has an average thickness of
around 5 km. This oceanic crust is much younger in
age than continental crust. It is formed from magma
at spreading centers and is subducted at oceanic
trenches, with the process being driven by mantle
convection. The oldest oceanic crust on the Earth is
only 200 million years old, although most is subducted
before it reaches this age (Price 1978). Projecting
from this maximum 200 million date and holding the
present tectonic activity as a constant, in the 4.6
gigayear history of the Earth, the oceanic crust may
have been recycled a minimum of 23 times.
Though the actual amount of cycling may be nearly
twice this figure, as during the Archean era, crustal
cycling is thought to have been much more vigorous
(Jacobs 1987). Others think the oceanic crust at this
time would be warmer and more buoyant thus less likely
to subduct as a plate. Subcrustal delamination after
massive flood lava resurfacing likely was the main
30


mechanism of heat removal and crustal recycling at this
time (Davies 1992).
The mantle is divided into two main zones, the
upper mantle and lower mantle. The upper mantle consists
of several zones and extends down to 660 km. The
asthenosphere begins the mantle and is thought to be
1% to 10% partially molten, due to is weak and low
velocity seismic waves. The asthenosphere is the source
of basaltic magma which forms the oceanic crust and
its main mineral is olivine, (Fe,Mg)2SiO^. At around
260 km the asthenosphere ends as a more solid phase
begins.
Between 380-400 km another mantle phase change
occurs as seismic waves rapidly speed up. This phase
is believed to mark the mineral precipitation of spinel
and the formation of denser ringwoodite from olivine.
Below this zone seismic waves show a gradual increase
with increasing pressure. The upper mantle ends at
around 660 km, where a chemical change of IV^SiO^-
ringwoodite to (Fe,Mg)SiO^- perovskite and (Fe,Mg)0-
magnesiowustite occurs.
The chemical phase change of olivine to the denser
perovskite and magnesiowustite, results in an increase
in seismic wave speed and marks the beginning of the
lower mantle. The lower mantle is thought mainly made
up of perovskite and magnesiowustite, which makes this
mineral assemblage the majority of the Earth by mass.
The ratio of iron to magnesium in these two minerals
is around 1 Fe for every 9 Mg (Merrill 1996). Seismic
studies have found the density increase of the lower
mantle also prevents the penetration of younger
subducting oceanic crust and this crust ends up lying
31


at the base of the upper mantle until it melts and
returns to the asthenosphere.
The lower mantle extends down to around 2890 km
and only the oldest and coldest of oceanic crust can
subduct into the lower mantle and down to the core mantle
boundary (CMB). The CMB region has been found to have
unique topographic and seismic properties, which are
believed caused by this subducting older oceanic crust.
As this crust reaches the CMB it thrusts into the molten
outer core making antimountains. As the hotter core
melts these plates, the melt migrates to areas of
elevation making antioceans.
When enough melt accumulates at an antiocean, it
begins to rise into the mantle to form plumes. These
plumes are shaped much like giant mushroom clouds
produced in large explosions and move through the mantle
in a similar manner the cloud moves through the
atmosphere. These plumes slowly rise up through the
mantle and eventually reach the surface. At that point
they are thought to produce huge formations of flood
lavas such as the Columbia Plateau. After the flood
lavas end, a hot spot or chimney of the mushroom cloud
remains in the mantle for many millions of years,
allowing melt to rapidly rise directly from the CMB.
The Hawaiian Island chain was believed to have formed
by this process, as the oceanic plate moved over the
relatively stable hot spot. By some estimates, over
one half of all core generated heat is removed by the
plume and hot spot process (Orson 1999).
Recent studies of high-pressure diamond-cell
experiments indicate that perovskite does not break
down to (Fe,Mg)0 and Si02 at up to 100 gigapascals (GPa)
32


and 3000 K (Serghiou 1998) conditions similar to the
bottom of the lower mantle. Due to equipment
limitations, conditions of 136 GPa and 4000 K 25%
(Merrill 1996) at the CMB have not yet been tested.
However, as no MgO was detected in the experiments,
it is likely perovskite may remain stable at the CMB
(Serghiou 1998). This is of great significance in
determining which eutectic melt dominates the outer
core.
Studies of osmium isotopes indicate not only that
plumes and hot spots likely rise from the CMB, but
include from 0.5% to 1% outer core material as they
rise (Brandon 1998). This outer core material is likely
the source of the iron in the mantle and is primarily
held in the minerals of FeO, FeSiO-., and FeSiO. In
Mercury where significant mantle convection was thought
absent, no iron at all has been detected in its surface
rocks by spectral analysis.
This likely inclusion of outer core material in
convection is important because if sulfur held as FeS
was the main eutectic component of the outer core, its
expression in the hot spot volcanoes would likely be
magnitudes greater than what is currently observed.
Sulfur concentrations are highest in andesite volcanoes
formed by subduction zones, not hot spot volcanism.
Analysis of Io volcanism later in the paper also
supports this view.
This leaves oxygen in the form of FeO as the
predominate eutectic element in the outer core. This
conclusion is also supported by the FeO version of
magnesiowustite being in plentiful supply at the CMB,
where it can diffuse into the outer core. Additionally,
33


Table 5 Some Estimated Parameters for the Earth's Core
Location Radius Density (km) (E3 kgiri ) Pressure (Ell Pa) Gravity (ms Z) Incom. Rigidity (E11 Pa)(Ell Pa)
Earth 1s center 0 13.89 3.639 0 14.253 1 .761
Inner core outer core "boundary" 1221.5 1221.5 12.764 12.582 3.288 3.288 4.40 4.40 13.434 13.047 1 .557 0
Outer core mantle "boundary" 3480.0 3480.0 9.904 5.565 1 .358 1 .358 10.68 10.68 6.441 6.556 0 2.938
Top of D" 3630.0 - 1 .268 10.48 6.412 2.899
(after Merrill 1996)
Table 6 Estimates of Some Properties of Earth's Core
Mean radius of Earth 6371 km
Depth to outer core 2891 km
Depth to inner core 5049 km
Composition Primarily Fe, a few % Ni, and approximately 10% of S, 0
Electrical conductivity 6xE5 S/m
Adiabatic temperature Between 0.7 and 1.0 C /km
Temperature at core mantle boundary Probably 40001000C
Viscosity of outer core 0.06 poise..
Mean density of outer core 1 0xE3 kg/ni 3
Density contact across inner core boundary 0.5 to 0.63xE3 kg/ni
Pressure, core mantle boundary 136 GPa
Pressure, inner core boundary 328 GPa
Pressure, Earth's center 367 GPa
(after Merrill 1996)
34


the temperature of 4000 K 25% (Merrill 1996) of the
outer core is sufficiently hot to have FeO operate as
a eutectic element.
There may be a regulating mechanism by which the
strength of mantle convection not only determines the
level of iron in the mantle, but the level of oxygen
(FeO) in the outer core. This is very significant for
the other terrestrial objects, as having FeO as the
main eutectic element greatly increases the level of
internal heat needed to keep an outer core molten and
a geomagnetic dynamo operating.
The core is divided into two zones, a molten outer
core and solid inner core. The molten outer core is
around 2080 km thick, consisting primarily of iron with
around 10% lighter elements (Stacy 1992). In most
theories the heat by which the outer core remains molten
and generates the geomagnetic dynamo comes from two
main sources. The first is the heat of fusion from
the crystallization of the iron inner core from the
outer core material. The second is buoyancy currents
generated by the lighter melt (higher in eutectic
elements) formed at the crystallization boundary.
As explored earlier in the heat budget, these
sources are insufficient to have retained a magnetic
field to the present time or even kept the outer core
molten in the Earth. That the temperature of the outer
core has remained relatively high while the mantle has
cooled significantly, indicates the likely presence
of another core heat source. Further support comes
from paleomagnetic fossil fields in rocks, which
indicates the magnetic field of the Earth has been in
35


existence to within 2 magnitudes of the present field
for at least 3.5 gigayears (Jacobs 1987).
The solid inner core of the Earth is around 1220
km thick and consists primarily of iron, with around
4% nickel (Stacy 1992). The inner core has a clear
anisoptropy, by which differential inner core rotation
has been measured. Measurements of differential inner
core rotation range from 3 to 0.2 per year (Song 1998).
In most dynamo theories an inner core is also necessary
to produce a magnetic field (Jacobs 1987). The cause
of the anisoptropy and differential rotation is
still under debate.
3.5 Venus
Venus is nearly the twin of the Earth, with almost
the same density, varying by only 3%. Venus also has
81% the mass and 88% of the gravity of Earth (Murray
1981). However, Venus rotates in a retrograde manner
every 243 days and has an orbital eccentricity of .0065.
Its orbital inclination to the ecliptic is 323' and
the inclination of Venus' equator to the orbital
plane is 2.2.
The surface of Venus is quite different from the
Earth's, as Venus lacks the tectonic features of
upwelling ridges and subduction trenches so prominent
on the Earth. The features which are present, quite
possibly indicate some magnitudes smaller amounts of
heat have been emitted from the interior of Venus, as
compared to the Earth. From data collected it appears
the surface of Venus lacks areas of differentiated
aluminum/silicate continental and oceanic basalt type
36


crusts, which create a bimodal distribution of surface
height on the Earth.
The data gathered by the Venera surface probes
and radar analysis, shows nearly the entire surface
area of Venus resembles the basaltic oceanic crust of
the Earth, although this crust appears to have a higher
level of silicates and is produced mostly by flood lavas
(Cattermole 1994). Close radar examinations of the
surface of Venus, along with crater analysis, appears
to indicate there has been little if any tectonic
activity for a minimum of 700 million years (Stacy 1992).
Most of the surface area of Venus which is lowlands,
appears to have been formed by repeated outpouring of
flood lavas and other volcanic features. The several
areas of highland are partially volcanic in origin and
others have features of complex block faulting, as if
oceanic type crust, that could not subduct was pushed
together into a mass of complex block faulting.
One recent hypothesis holds that periodic
catastrophic resurfacing occurs on Venus every several
hundred million years. However, a close examination
of surface features, such as partial flooded impact
craters and the coronae, tend to indicate that a more
gradual process of surface modification is a more likely
scenario for Venus (Cattermole 1994). Careful orbital
tracking of the Magellan Radar Mapper has found areas
of relatively low density under surface features on
Venus, most of which are located below regions of
elevation on the surface of Venus. These elevations
are thought to be sustained by either masses of low
density material rising from within the mantle or by
plugs of low density minerals. However, sizes, mineral
37


types, volcanic activity and compensational factors,
make it unlikely that solidified low density minerals
are underlying the crust (Cattermole 1994).
What Venus does appear to show, is a mantle diapier
(plume) tectonic process. It has been hypothesized
that large "blobs" of lower density material from the
mantle which is presumably molten, have risen to form
"blisters" under the crust of Venus. This process is
likely similar to plumes rising through the mantle on
the Earth, but on a somewhat smaller scale (Cattermole
1994). These low density areas are usually elevated
and are associated with numerous volcanic features.'
Often found around these areas are strange cross-hatched
faulting, believed caused by subsurface expansion.
Additionally, these areas have numerous- and unique
coronae, which are also thought to be formed by a
volcanic upwelling process (Cattermole 1994).
In some ways these areas of greatest elevation,
resemble the Syrian and Elysium rises on Mars, which
contain the gigantic shield volcanoes that are thought
to have once been located over hot spots in the mantle
of Mars. Areas of elevation on Venus appear to be either
volcanoes with somewhat similar forms of expansional
faulting, though many areas of elevation have complex
faulting that appears compressional. It is unlikely
that low density minerals underlie these areas, due
to their shape and point concentration. Other factors
such as the surface rocks of Venus being up to ten
times more ridged than on the Earth due to the
absence of water or the high temperature of the
rocks may play a part.
38


The intense heat of the atmosphere of Venus would
tend to make its crust more buoyant than Earth oceanic
crust. This may reduce the possibility of Venus' crust
being subducted and forming a differentiated crust.
Additionally, the intense heat of Venus could make it
more likely for rocks to become molten from internal
heat at a very shallow depth and help prevent tectonic
plate formation similar to that of the Earth's.
The early history of Venus likely resembled the
early Earth's environment for perhaps a half billion
years and during that time they should have had similar
atmospheric conditions. However, if higher temperatures
due to the orbital location of Venus prevented the
formation of liquid water, carbonate minerals could
not form to sequester the carbon dioxide. It is also
thought that the presence of water within rocks assisted
in the chemical differentiation of the crustal rocks
on Earth. The absence of liquid water therefore may
also help explain the surface features of Venus.
The much lower level of chemical differentiation
in the crust of Venus could also be an indicator that
much less tectonic activity has occurred on Venus
compared to the Earth. The crust of Venus appears to
have cycled very little, perhaps, not even once. Later
modification appears more characteristic of repeated
flood lavas and numerous hot spots. Venus may be an
example of what the Earth appeared like very early in
its history or what Io is today.
Why Venus which is nearly the twin of Earth
compositionally, has such different tectonic features
and history could be due to lesser amounts of heat
evolving from its interior. As stated before, one
39


possibility for this tectonic difference, is that much
less heat has been generated in the interior of Venus
as compared to the Earth. It must be noted that Venus
rotates very slowly and does not have a CLOP. The enigma
on how the Earth has acquired the heat needed to account
for its apparently more vigorous tectonic history, as
well as the source of energy needed produce the magnetic
field of the Earth remains.
40


4. Close Large Orbital
Partner Hypothesis
4.1 Close Large Orbital Partner
(CLOP) Process
The thesis of the paper, the retention of magnetic
fields in rotating terrestrial objects through the
actions of a close large orbital partner or CLOP
hypothesis, can help account for much of the excess
core heat theoretically needed to retain the magnetic
fields of Mercury, Ganymede and the Earth to the present
era. This CLOP process is driven by the transfer of
angular momentum from the rotating planet to its core,
through the actions of the CLOP. This is likely a
relatively weak transfer of energy in comparison to
most other tidal based energy transfers.
Although the energy transferred by the CLOP process
appears to assist in producing magnetic fields of around
600 to 750 nT in Mercury and Ganymede respectively
(Murray 1981, Kivelson 1997), it is apparently incapable
of adding enough internal heat to result in surface
tectonic or volcanic modification of these bodies over
geologic history. The amount of heat generated by the
CLOP process within these bodies is evidently low enough
to be lost by radiative dissipation. Thus mantle
convection with its possibilities of surface
modification is avoided.
The Earth with a faster rotation rate relative
to its CLOP, may allow the CLOP process to generate
41


significantly more heat in its core. The greater mass
of the Earth may also make radiative dissipation a less
effective process, so heat produced by the CLOP could
accumulate and help drive mantle convection and thus
affect surface morphology. This may help explain the
greater tectonic activity of the Earth over its history
as compared to its near twin Venus.
The CLOP process occurs through gravitational
distortions produced on the solid inner core of a planet
by its CLOP and is a tidal effect. As the solid inner
core is encased in a molten liquid outer core, it is
able to move independently and be distorted by the CLOP.
This interesting gravitational distortion causes the
inner core to be ever so slightly distorted into an
asymmetrical sphere or "pear like" shape with the
larger side facing of the asymmetry facing the CLOP.
This asymmetrical distorting effect is similar
to the "pear like" shape of the gravitational/tidal
locked Moon of the Earth. Although the Moon's
asymmetrical shape is tilted a bit to its left face
or more accurately the direction of the tidal bulge
overshoot by which the Earth transfers angular momentum
to the Moon. This asymmetrical tidal bulge can be
observed in Lunar gravitational profile of the face
of the Moon as shown in Figure 2 on the next page.
The smooth circular line in Figure 2 represents an
ideal spherical Moon.
The gravitational forces of the Earth, being
strongest on the near side of the Moon, creates an
asymmetry to the tidal bulges on the Moon. This causes
a measurably greater mass on the side of the Moon facing
the Earth, than on its opposite side. As the rotation
42


Asymmetry of Lunar Face
9C
Ftgure 2. Apollo mission radar sounding profiles around lunar center cl mass
(after Murray. 1981 }


of the Moon relative to the Earth is synchronous with
its orbital period, the bimodal tidal cycle so familiar
on the Earth is absent on the Moon and this greatly
changes tidal dynamics. This asymmetrical mass
distortion is the mechanism by which the Moon's rotation
and orbital period are kept in synchronicity.
This asymmetrical distortion has effected the
geology of the Moon as well and is the reason the Mare
lavas are nearly all found on the side of the Moon facing
the Earth and on average, the leading side or to the
left of the Lunar face we observe. This is due to the
transfer of angular momentum to the Moon from the Earth,
being focused on the left frontal hemisphere as shown
in Figure 2.
These Mare lavas also indicate the Moon at some
time rotated relative to the Earth, allowing the Moon
to sustain a magnetic field for up to perhaps, a billion
and a half years after its formation (Murray 1981).
The rigidity of the Moon prevented it from fully matching
the asymmetrical gravitational distortions caused by
the Earth after its rotation ceased. To compensate
for this rigidity limitation, the vast flood lavas of
Mare poured out from the interior of the Moon in an
attempt to match the gravitational distortion. The
sudden appearance of the Mare lavas 3.9 billion years
ago, can give a rough estimation when the Moon stopped
rotating relative to the Earth and assumed its present
gravitational locked alignment.
4.2 Tidal Torque
The original orbit of the Moon after it coalesced
from the fragments of ancient protplanetary collision,
44


is thought to have been around twice as close to the
Earth as it is today (Stacy 1992). As the orbit of
the Moon is slower than the rotation speed of the Earth,
the Earth has been transferring angular momentum of
its rotation to increase the angular momentum of the
Moon. This transfer results in a rotational slowdown
of the Earth and an orbital distance increase in the
Moon.
This transfer of angular momentum is often called
tidal torque. As illustrated in Figure 3, the
gravitational force of the Moon raises a tidal bulge
on the Earth. However, due to the rapid rotation of
the Earth and associated dissipative effects, the average
high tide will occur a few minutes after a direct
alignment with the Moon. The gravitational force of
this offset tidal bulge causes an orbital accelerating
force on the Moon, while slowing the rotation speed
of the Earth.
As the angular motion is transferred to the Moon,
the orbit distance of the Moon gradually recedes from
the Earth. This process is believed to have nearly
doubled the orbital distance of the Moon from the Earth,
by transferring around 4.6 E12 26% W of power of angular
momentum to the Moon during geologic history (Stacy
1977). It is important to note, this is not the
process by which the CLOP process transfers energy
to the inner core of the Earth.
4.3 The CLOP Process
As discussed before, the CLOP causes the
asymmetrical "pear like" distortion of the inner core,
encased within the molten outer core. A simple physical
45


demonstration will show that an off-center sphere inside
a larger rotating sphere, will be forced to rotate faster
than its enclosing sphere. Through this process, the
effects of the CLOP cause a transfer of angular momentum
from the planet to the inner core.
This has the net effect of slowing down the rotation
speed of the majority of the planet, while increasing
the rotation speed of the inner core. The increased
angular momentum of the inner core is dissipated through
friction and the formation of currents at the inner
core/ outer core surface boundary.
The concept may be simple in principle, but is
quite complicated in reality. Consider the perturbing
effects of the Earth's axis of rotation being tilted
at 23 to the orbital ecliptic. The Sun can also be
considered an Earth CLOP, as its gravity contributes
to around a fourth of the tidal effect on the Earth.
Added to this perturbation is the Moon orbiting the
Earth at 6 off from the solar ecliptic. These
differences would cause the center of the asymmetry
in the core to change relative to its equator in a highly
complex, but periodic manner. The differentially
rotating core's axis of rotation would likely be pulled
off center from the planet's axis of rotation and follow
a somewhat chaotic pathway, which may be similar to
the wandering of the magnetic poles.
Another gravitational distortion that would effect
the level of asymmetry of the inner core and therefore
differential inner core rotation, is produced by tidal
force differences between two or more CLOPs. In the
case of the Earth/Moon/Sun system, when both CLOPs are
on one side of the planet, at right angles, or in
46


opposition, increased or decreased gravitational forces
will be produced. On the surface of the Earth, we see
this in the full and neap tides, similar variations
in core asymmetry would likely be produced as shown
in Figure 4. These variations in the asymmetrical
distortion could also effect the currents in the molten
outer core and may help to explain the daily, monthly,
and other periodic variations in the strength of the
magnetic field of the Earth.
Some have hypothesized the energy dissipation
generated by the semi-dinural tides in the Earth's
core is driving the geomagnetic dynamo and this tidal
mechanism could generate a mean liquid current flow
of several cm sec in the molten outer core (Houben
1975). The solar and lunar tides deform the Earth's
mantle at the core mantle boundary by several centimeters
(Houben 1975). A similar condition is also generated
at the inner-outer core boundary. These conditions
have the effect of imposing a radial boundary condition
on the viscous, rotating velocity field within the
outer core.
If the outer core is held as an incompressible
fluid, any phase lag delay between the two boundaries,
can generate a mean current of several cm sec-1 between
them (Houben 1975). For a compressible fluid outer
core, a single phase lag relative to the tidal potential
could drive a current. These researchers used a
two-dimensional cartesian "channel" model with the tidal
motions to show Reynold's stresses could drive mean
flows (Houben 1975). They also hold these currents
are significant enough to explain the westward drift
of the geomagnetic field and generate enough energy
47


Tidal Torque Acceleration of the Moon
Figure 3. Tidal torque is due to a lag in the tidal bulge of the Earth relative to the
Earth-Moon axis causing an acceleration torque on the Moon. The tidal torque lag
angle of around three degrees translates to a twelve minute delay in high tide from the
axis alignment. (after Stacy, 1992 )
Figure 4. Variations in CLOP Influence on the Earth
LOW
MEDIUM
HIGH
Sun EarthMoon
Sun---Earth
Sun--Moon--Earth
Moon
Note: These variations are periodic in nature
48


in the core to drive the geomagnetic dynamo (Houben
1975). This model has some limitations due to its age,
as the recent data of a varied CMB topography and
differential core rotation are not taken into account
in the model.
4.4 Differential Core Rotation
It has been discovered relatively recently, that
the inner core of the Earth does indeed rotate faster
than the rest of the Earth (Song 1996). This relatively
faster rotating inner core was detected due to an
anisotropic anomaly in the inner core (Song 1996).
Song and Richards recently found that seismic waves
transversing the Earth have shown small variations over
the last several decades. This increase in velocity
in one direction or anisotropy, is tilted 8 to 11
from the Earth's axis of rotation and migrates eastward
at around 1.8 per a year (Song 1996), completing an
independent rotation every 200 years. Later studies
by other scientists put the complete differential
rotation at once every 120 years (Su 1996).
Other studies of the possibility of differential
core rotation have shown a rotating liquid sphere will
cause coil currents perpendicular to the axis of rotation
to form (see Figure 5), but a model of this effect on
the Earth's outer core had not been worked out.
Unfortunately these coil currents are unlikely to
cause a magnetic field similar to the Earth's, as
each coil would have an independent and mostly
internalized magnetic field.
A similar coil generating process is believed to
occur in the Sun and Jupiter, as their cores rotate
49


Figure 5. Convection Coils in a Rotating Sphere
i
i
Possible structure of Earth's outer core coil
currents at alligned rotation. ( after Stacy, 1992 )
50


faster than the surfaces of these bodies. Sunspots
may form as surface features of these internal coils.
As these coils become distorted by continuing
differential rotation, the magnetic field collapses
to release their energy in solar prominances during
certain times in the sunspot cycle of the Sun. On
Jupiter, these coils may help form the colorful
multi-band surface wind patterns and help explain its
variable magnetic field.
Interestingly, a year or so before the discovery
of the migrating anisotropy, synchronously two sets
of geophysicists researching core dynamics with complex
computer simulations predicted that the inner core of
the Earth should rotate a bit faster than the rest of
the Earth (Glatzmaier 1996). They hypothesized this
differential rotation was due to magnetic torque
generated by east moving currents in the outer core.
Unfortunately, an explanation on the source of energy
to generate these evidently vigorous currents causing
the torque remains a bit weak, as some of their
constraints such as outer core viscosity are unrealistic
(Glatzmaier 1996). Other studies found efficiencies
of magnetic field generation of 5% for heat driven
mechanism and only slightly higher efficiencies for
gravitational driven processes (Stacy 1992).
With the known energy sources inside the core
already evidently deficient from a heat budget
examination, the addition of another substantial energy
drain can only increase the deficiency. This concept
of magnetic torque without an adequate energy source
to drive the original magnetic field generation and
51


torque causing currents, might be a case of the
proverbial tail wagging the dog.
A clear mechanism of how a planetary magnetic field
is produced within the Earth by a differentially rotating
inner core is uncertain. However, if the axis of
rotation of the inner core is slightly offset from the
planet's axis of rotation, other possibilities exist.
As an internally rotating sphere's axis is moved away
from a perpendicular orientation to the encasing liquid
sphere's axis of rotation, the numerous coil currents
which once formed around the rotating sphere, would
be tilted and likely would migrate around the sphere.
As these migrating coils move around the core, they
would appear to form in what in essence is a giant coil.
A similar giant coil is perhaps, the source of
the self-exciting dynamo of the Earth. As the center
of this giant compound coil is blocked by the solid
core, the liquid current is prevented from returning
through the center of the compound coil to internalize
the magnetic field. Consequently, the magnetic fields
are expanded outward with a combined magnetic energy
of all the rotating coils.
There is geological evidence in support of this
possible core current structure. It is known from the
geological record, as the magnetic axis of the Earth
moves away from the rotation axis, the strength of the
magnetic field of the Earth increases. There is some
evidence to indicate that when the magnetic axis and
rotation axis of the Earth are aligned, the Earth's
magnetic field disappears (Press 1978). Ganymede also
shows this effect as its magnetic axis tilted 10
relative to its axis of rotation. (Kivelson 1997).
52


CLOP theory may also help explain the periodic
reversals of the Earth's magnetic field. As the unstable
differentially rotating core is affected by various
gravitational fields and frictional forces, it will
tend to wander in semi-periodic cycles. Occasionally,
the axis of rotation of the inner core will align with
the axis of rotation of the planet. At this point,
the magnetic field of the Earth likely will be
internalized within the currents of the core in a process
similar to the one illustrated in Figure 5. The magnetic
field of the Sun then becomes the dominant field on
the Earth.
As the axes of rotation again move apart, the
currents of the outer core will absorb and amplify the
polarity of the dominating magnetic field of the Sun.
If the magnetic field polarity of the solar wind is
reversed by chance from the former magnetic field
polarity of the Earth, the polarity of the planetary
field is reversed. The geologic evidence from fossilized
magnetic fields indicates the Earth's magnetic field
weakens before a magnetic polarity reversal occurs (Press
1978), but many cases of field weakening have not
resulted in polarity change. Far more study on fluid
dynamics is needed before the exact process by which
currents in the outer core produce a magnetic field
is known.
4.5 CLOP Efficiency
The CLOP hypothesis is an interesting concept,
but is it physically capable of generating a minimum
of 5.1 E12 W of power in the core of the Earth over
geologic history as the data in Figure 1 indicates?
53


As the CLOP process is a theoretically inefficient method
for the transfer of angular momentum, it would likely
constitute only a small fraction of the angular momentum
the Earth has lost over its geologic history.
Fortunately, there is a method by which the past
rotation rate of the Earth can be determined. This
is possible due to many organisms depositing daily growth
layers of calcium based compounds, which also show
seasonal variations. From this data, the number of
days in the year when the organism lived and therefore
the number of hours in a day can be measured. Fossil
coral and bivalves are particularly useful in this
regard, allowing a tracing of the history of the Earth's
rotation for around 500 million years (Broshe 1990).
Going further back in time requires some speculation,
in that no dramatic changes in the Earth/Moon system
have occurred. Extrapolation backward gives a rotation
rate of the Earth 4.5 gigayears ago at around 8 hours.
13% (Broshe 1990).
With this ancient rotation data and the present
rotation rate of the Earth, the amount of energy lost
over time or power can be estimated. A comparison of
this power loss to the power needed to balance the heat
budget (5.1 E12 W) can give potential limits on the
efficiency of the CLOP process. This calculation is
illustrated in Equation 1.
The calculation gives a total loss of energy due
to angular momentum decrease of 1.45 E13 W for the Earth.
If the minimum missing heat from the heat budget is
accepted as 5.1 E12 W, this gives a maximum efficiency
for the CLOP process of 35.5%. This is a rather high
54


Rotational Period (hours )
Figure 6. Earth Rotation In Past Extrapolated From Coral Data
-T=23.93 exp(0.0211t)
'"T=23.93 exp(0.0233t)
T=23.93 exp(0.0256t)
lO
in
( after Brosche, 1990 )


Equation 1 Efficiency of Earth/Moon CLOP Process
Determining the Power Loss in Earth's Rotational Speed
Ploss = AE/At
(Er,f Er,i)/At (P=power)
(1/2 Ifwf2 .5 Iiwi2)/At
Ji = !f = 2/5 Me Re =
= (2/5)(5 98 e24)(6.38 e6) = 9.74 e37 Kg m
wf = 2 /86400
2 -1
= 5.289 e-9 radians sec
(24 hour rotation)
w. = w ^ x 3
l f
2 -1
w. = 4.760 e-8 radians sec
l
(8 hour rotation)
t = 4.5 e9 years t = 1.418 e17 sec
missing heat budget figure = 5.1 e12 W (pneecje(j)
(W = Joules sec-1)
Px = (,5)(9.74 e37)(4.76 e-8 5.29 e-9) = 1.453e13
W
(1.418 e1 7)
% efficiency = P ,/P,
1 needed loss
% eff. = 5.1 el 2/ 1 .453 e13 = 35%
56


percentage for CLOP efficiency and is much higher than
originally hypothesized.
However, the accuracy of the heat budget data
used in the calculation is quite uncertain. Better
understanding of the estimated heat sources could easily
change the efficiency percentage. Additionally,
the amount of heat deposited, if any, in the mantle
due to daily and longer periods of non-CLOP tidal flexing
of the Earth over its history is not taken into account
in these calculations.
A rough approximation of CLOP efficiency for Mercury
can also be estimated from the Earth CLOP efficiency
calculation. For this calculation, one assumes the
CLOP effect is equivalent to the gravitational tidal
interaction on a solid core. This calculation is
shown in Equation 2.
From Equation 2 it is shown that the gravitational
tidal interaction of Mercury's CLOP the Sun, is
approximately three times the effect of the Earth's
CLOP the Moon. This translates into approximately a
12.8% efficiency for the CLOP process in Mercury.
However, due to the tidal flexing of Mercury's highly
elliptical orbit, the CLOP efficiency is likely a small
fraction of the estimated figure.
4.6 Evolution of a Terrestrial Planet
The CLOP process has implication for the geological
evolution of terrestrial object. A hypothetical scenario
for a generic geologic evolution of a terrestrial object
follows to illustrate the main possible fates. It is
a useful exercise, as it can help one understand the
possible causes of the differences between the
57


Equation 2 Approximate Efficiency for Mercury/Sun CLOP
(Assume CLOP efficiency is proportional to gravitational
tidal interaction on solid core of a terrestrial object)
F = F M m
core
orbit
Earth/Moon___________Mercury/Sun
Mass central 8.4 e23 Kg 2.0 e30
Mass core 8.0 e22 Kg * 2.7 e23
r core 1.4 e6 m ^1 .8 e6
r' orbit 3.84 e8 m . 387AU 6.0 el 0
G 6.67 e-11 6.67 e-
F =(6.67 e-11)(8.4 e23)(8.0 e22)(1.4 e6)= 1.1 e17
Newtons (3.84 e8)^
Earth CLOP
F = (6.67 e-11)(2 e30)(2.7 e23)(1.8 e6) = 3.0 e1 7
Newtons (6.0 e10) Mercury CLOP
E = 1 Earth eff. = 35% E = 0.366 Mercury eff. = 12.8%
58


terrestrial objects. This hypothetical evolution
scenario will only deal with internal dynamics and not
surface morphology.
Whether a homogeneous or heterogeneous accretion
process originally forms the hypothetical terrestrial
object, the object would soon becomes entirely molten
due to supernova generated radioactive elements and
heat generated during accretion. In this magma ocean
state, the object begins to chemically differentiate.
Eventually a state is reached in which an entirely
molten core forms of predominately molten iron/nickel
with perhaps up to 10% lighter elements, likely oxygen
or sulfur. Encasing the core is a ferro-magnesium
silicate mantle.
Convection in both the mantle and core begin to
cool the young terrestrial object. In 'the core, an
iron/nickel solid core begins to crystallize out of
the molten core. This solidification releases the heat
of fusion, as well as gravitational driven heat caused
by lighter chemical differentiated residues produced
at the crystallization zone.
When the inner core grows to some size, a planetary
magnetic field forms and likely grows as the inner core
grows. Convection continues to cool the terrestrial
object and the inner core grows ever larger. At some
time a separation in evolutionary history of the
hypothetical terrestrial object occurs depending on
whether a CLOP is present or not. Although it appears
a CLOP is necessary for the retention of a magnetic
field, it is uncertain if it is necessary for the
generation of a magnetic field.
59


If a CLOP is present, it will begin to effect the
inner core and produce frictional heating on its surface,
adding to the heat generating the magnetic field. As
the inner core grows, the effects of the CLOP will
grow until a point is reached at which the heat produced
by the CLOP stops any further crystallization of the
inner core. A steady state feedback process is created
and future core growth likely depends on the further
evolution of the CLOP system. The Earth, Mercury and
Ganymede are likely examples of this pathway of the
scenario.
If no CLOP is present, the inner core will continue
to grow until heat production lags because of increasing
concentration of the lighter eutectic compounds (FeO
or FeS), in the still molten outer core. At some point
the currents cease because of density differences and
the planetary magnetic field vanishes as heat production
stops within the core. Mantle convection likely
continues for some time, gradually slowing down and
the core becomes completely solidified. Any surface
modification of the planet by tectonic forces will end
as well, except perhaps for shrinkage faults as the
planet cools and becomes geologically dead. The Earth's
Moon and Mars are likely examples of this pathway of
the scenario.
60


5.
The Galilean Satellites
5.1 The Galilean Satellites
The Galilean satellites of Jupiter are perhaps
the most interesting and diverse set of bodies in the
solar system. Galileo Galilei discovered these four
bodies with his newly fashioned telescope in January,
1610. Besides being some of the first objects discovered
by the telescope, later observations of these satellites
by other astronomers led to the first measurement of
the speed of light. These bodies continue to surprise
astronomers and remain one of the key frontiers of
planetary research.
The Galilean satellites are substantial bodies,
with the inner two Io and Europa, being around the size
of the Earth's Moon, and the outer two Ganymede and
Callisto are around the size of Mercury. These bodies
show a compositional gradients as well, with the inner
two moons consisting almost entirely, of rock and metal.
The outer two moons are nearly half water ice by mass,
with the other half consisting of rock and metal.
Interestingly, the three inner Galilean moons
are chemically differentiated much like the inner planets
with the concentration of lighter elements increasing
while moving outward in the orbital sequence. The three
inner Galilean satellites have predominately iron cores
covered by silicate mantles and increasing amounts of
ice moving outwards from Jupiter. The outermost moon
Callisto is quite compositionally different, consisting
61


of a homogeneous mixture of rock and ice, with hints
of heterogeneous accretion.
This chemical differentiation is paralleled
by the inner three moons being in a Laplace orbital
harmonic system, while Callisto orbits in an independent
manner. A Laplace orbital harmonic system is named
after the individual who discovered the orbital
harmonics of the three inner Galilean satellites.
In this orbital system for every one orbit of the
outer most satellite Ganymede, the next inner satellite
of Europa orbits two times and Io the innermost orbits
four times.
Surprisingly, two of these moons Io and Ganymede,
were discovered to have intrinsic magnetic fields, by
the aptly named Galileo orbiter. Although both these
moons have dipole movements of nearly equal strength,
the ambient magnetic fields experienced by these
bodies greatly differ (Jones 1997). Ganymede
appears to generate its magnetic field through a
dynamo process similar to the Earth's. Io's magnetic
field generation is more problematic and is likely
produced by magneto-convection, a process generated
by the strong ambient magnetic field of Jupiter
(Jones 1997).
A short description of each Galilean satellite
follows to familiarize the reader with the unique
features of each body. Then we explore possible
scenarios on the orbital evolution of these bodies
and how the CLOP process might function in this
system to produce magnetic fields. The comparisons
on Table 7 can assist in this endeavor.
62


Table 7
Basic Properties of the Galilean Satellites
Io_______Europa Ganymede
Orbital 1.77 3.55 7.16
Period (days)
Orbital Distance 4.22E5 6.71E5 10.7 E5
from Jupiter (km)
Orbital Distance 5.9 9.4 15.0
Jupiter Radii
Eccentricity 0.0
0.0 0.002
Eclptic 0
Inclination
0.5 0.2
Size (km) 1821
1565 2635
Density 3.53 3.02
Differentiation 0.378 0.347
C/MR2 0.007 0.014
1 .94
0.194
0.003
Callisto
16.69
18.8E5
26.4
0.008
0.2
2360
1 .85
0.185
0.03
63


5.2 Io
Io is by far the most geologically active body
in the solar system. This is supported by the absence
of impact craters and the presence of many active
volcanoes. Io1s surface is covered by volcanic landforms
of vents, calderas, lava flows and volcanoes. This
is not surprising, as Io's heat flow is estimated at
_2
2.5 W m ,30 times the Earth's average (Jones 1997).
Although its colorful surface is covered with sodium
compounds, sulfur and sulfur compounds, heat measurements
of 700 K to 2,000 K lavas from the Galileo orbiter
indicate silicate volcanism is active on Io (McEwen
1998). Some of these lavas are hotter than the hottest
of Earth lavas, and have been tentatively identified
as magnesium-rich othopyroxene lavas (McEwen 1998).
The temperatures of these lavas is well above the boiling
point of sulfur in a vacuum (McEwen 1998) and likely
sulfur constitutes the majority of the material in the
gigantic volcanic plumes of some vents, which rise a
100 km above the surface of Io and rain down over an
area 300 km wide (Greeley 1994).
The source of energy driving this massive volcanism
is thought to be derived by the tidal flexing of Io
between Jupiter and its Laplace partners, Europa and
Ganymede. Calculations estimate the heat generated
1 3
by this tidal flexing at 10 W, two to three orders
of magnitude greater than any potential radioactive
heat sources in Io (Greeley 1994).
One of the most interesting features of Io is the
presence of an intrinsic magnetic field. The magnetic
signature of Io detected by the Galileo orbiter was
antiparallel to Jupiter's, indicating the existence
64


of an intrinsic magnetic field. The magnetic fields
measured at Io decreased around 40%, but rotated very
little unlike Ganymede (Gurnett 1997). Unfortunately
the very high ambient field of Jupiter, prevented
determining if the magnetic field of Io is generated
by a dynamo process or is due to magneto-convection.
This magnetic field is likely not produced by remnant
magnetism, as the high surface heat flow of Io at 2.5
_ 2
W m leaves all but the last two km of Io above the
Curie point (Greeley 1994).
This high tidal generated heat also likely makes
the internal structure of Io a bit different than
Ganymede or the Earth and is reflected in the moment
of inertia of Io at 0.378. The moment of inertia
measures the concentration of mass within a body and
2
is generated by the formula ( C/MR = ). C is the
bodies axial moment of inertia, M is mass of body,
and R is radius (Anderson 1998).
A moment of inertia result of 0.4 indicates a
homogeneous body. Chemically differentiated bodies
such as Earth (0.33), Ganymede (0.311), and Europa
(0.347) have a lower moment of inertia numbers (Anderson
1997). Io is differentiated due to its moment of inertia
number of 0.378, but perhaps not to the same degree
as these other bodies. The moment of inertia for
Callisto is in dispute and may range from 0.40 to
0.358 and is influenced by high density ice phases
(Anderson 1998).
Io is thought to currently have a predominately
iron core of at least half its radius and is encased
in a silicate mantle (Sarson 1997). Io's moment of
inertial (0.378) is significantly higher than the other
65


terrestrial bodies of Earth and Ganymede (0.33, 0.311),
which have dynamo produced magnetic fields, and is
relatively closer to a homogeneous body (0.4). The
likely reason for this chemical differentiation
difference is the high internal heat of Io. This intense
heat may cause Io's metallic core to currently be
entirely molten, with any lighter eutectic elements
being well distributed within this core, resulting in
the low 0.378 moment of inertia figure.
In many ways, Io may resemble the structure of
an early terrestrial body like the Earth, soon after
differentiation in a near magma ocean state. This is
supported by lava temperatures of 1700 to 2000 K, which
are thought characteristic of primitive, magnesium-rich
komatiite magmas (Wilson 1998). These magmas formed
from the partial melting of the mantle during the early
history of Earth. Given what is known about the
formation of this variety of magma, at least 40% of
the mantle of Io should be partially melted (Wilson
1998).
Observations from Io may also give insight into
early Earth history, as spectroscopic data finds the
presence of silica and alkali-rich rocks in regions
far from currently active volcanoes (Wilson 1998).
These areas as associated with mountainous material
forming standing blocks of high rugged relief. The
mountainous masses do not appear to be formed by volcanic
processes and can exceed 9 km in height and 100 km across
(Greeley 1994). These masses also appear to be the
oldest terrain on Io due to embayment relationships
with the surrounding plain (Greeley 1994).
66


The early formation of continental rocks on Earth
is also likely, as determined from measurements of Nb/U
ratios of ancient Australia rocks. These Nb/U ratios
indicate nearly the same amount of ancient continental
crust as exists today (Hofmann 1997). No evidence of
tectonic plate subduction and spreading centers exists
on Io, instead a rapid burial and recycling process
seems to be occurring (Wilson 1998). The interesting
structure of Io also supports the idea of a primitively
differentiated Venus and gives more support for the
CLOP hypothesis.
Io also gives some evidence that sulfur may not
be the main eutectic forming element (FeS), but rather
oxygen (FeO), is the main eutectic forming element.
In iron meteorites, concentrations of sulfur are very
low, usually below 0.1% and in rocky irons it increases
to around 1 % of all iron bound up as FeS (Lewis 1 993).
The observed sulfur deposits on the surface of Io and
its apparent restriction to the near surface lithosphere
due to high mantle temperatures, may indicate its likely
location in other terrestrial bodies. If Io is indeed
a possible model for the early Earth, it appears sulfur
would be expelled from the early core and limited to
the extreme upper mantle. Currently on the Earth, the
majority of the sulfur may now be concentrated in the
oceans and asthenosphere.
5.3 Magneto-Convection
As it appears a solid inner core is needed for
a self generating magnetic dynamo to exist, a
magneto-convection process generation the intrinsic
magnetic field of Io is a more probable scenario.
67


Added support for this magneto-convection process, is
the heat produced by tidal interactions in Io's
mantle would inhibit the transfer of heat from the
interior, preventing vigorous convection (Sarson 1997)
and resulting in raising core heat.
A magneto-convection process refers to the
convection of an electrically conducting fluid, such
as an entirely molten metallic core, that is effected
by an imposed magnetic field such as Jupiter's. The
currents in the convecting medium perturb the imposed
magnetic field, allowing a magnetic field to be produced
in the medium of around the same order of magnitude
or smaller as the imposed field. If the imposed magnetic
field is removed in magneto-convection, the induced
field disappears as well. There is no self sustenance
of the magnetic field, as the convecting medium by itself
can not produce a magnetic field. One way to determine
if magneto-convection is the source of the magnetic
field of Io is to have a space probe fly by Io during
the occasional times when the magnetic field of
Jupiter collapses.
5.4 Europa
Europa has the smoothest surface of any known solar
system body, with a relief of less than 200 m (Greeley
1994). Its surface is entirely of ice and from the
rarity of impact craters on the surface of Europa, it
is likely less than 10 million years old (McKinnon 1997).
In many ways Europa's surface resembles an arctic pack
ice, with lighter large plates of ice bounded by lanes
of darker younger ices. Other structures exist which
appear to be some type of icy volcanic flow (McKinnon
68


1997). These features have led many scientists to
hypothesize there is a global ocean 10 to 30 km below
Europa's icy surface.
Moment of inertial information (0.347), from the
Galileo orbiter, indicates Europa likely has a three
layer structure of a large metallic core encased in
a silicate mantle and covered by ice or water layer
of approximately a 100 km thick (McKinnon 1997). The
source of heat keeping a liquid ocean present is likely
tidal flexing heating similar to what is occurring on
Io, though of a much lesser magnitude due to Europa's
greater orbital distance from Jupiter and position in
the Laplace orbital system.
Although the Galileo orbiter did not find an
intrinsic magnetic field around Europa, it did find
perturbations in the Jovian magnetic plasma field
suggestive of an weak electrically conductive layer
(Kivelson 1998). The weakness of the perturbation and
inclination with the Jovian field support this
finding (Khurana 1998). This electromagnetic induction
requires eddy currents to flow inside the moon and this
could be support for a salt rich global ocean under
Europa's icy surface.
5.5 Ganymede
Ganymede is the largest and most massive of any
satellite in the solar system. It also has the highest
density differentiation of any body in the solar system,
with a moment of inertia of 0.311. The metallic core
and silicate mantle of Ganymede is estimated at 1800
km in radius, and is covered in a 800 km thick layer
of ice, with possibly a global ocean.
69


The surface of Ganymede has had significant geologic
modification and consists of two distinct terrain types,
both of clean ice. The ancient darker heavily cratered
terrain is considered the surface formed after chemical
differentiation. This is supported by the low relief
of this terrain, as higher density undifferentiated
primal crust is unlikely to be well supported by
underlying nearly pure ice produced by differentiation
(Showman 1997). Additional support comes from the
darker terrain having approximately half the crater
density as the undifferentiated primal surface of
Callisto, indicating it is a modified and younger
surface (Showman 1997).
The second lighter grooved terrain constitutes
around 60% of the surface of Ganymede. This lighter
grooved terrain is characterized by numerous subparallel
ridges of 100 km or less, separated by 3 to 4 km.
Average relief between ridges is low at 300 to 400 m
(Greeley 1994). Estimates of the age of this terrain
is a billion years or less, from 10 km cratering rates
(Showman 1997).
The magnetic field of Ganymede was found to be
around 1.4% the Earth's, with equatorial field strength
of 750 nT (Gurnett 1996). The magnetic field of Ganymede
was also found to be tilted at 10% relative to its axis
of rotation (Kivelson 1996). This tilt, along with
the high degree of chemical differentiation in Ganymede,
makes a dynamo process similar to the Earth's the most
likely cause of magnetic field generation in Ganymede.
Ganymede presents a bit of a mystery, as it is
a highly centrally concentrated body, while its neighbor
Callisto is homogeneous. The differentiation in Ganymede
70


also appears to have occurred soon after accretion of
these bodies. There is a slight difference in
composition between these two bodies of nearly the same
mass and density, with Ganymede having a 55/45 rock
to ice ratio and Callisto a 45/55 rock to ice ratio
(McKinnon 1997). This ratio may appear to violate the
3
bodies close densities of 1.94 to 1.85 g/cm but the
presence of dense ice phases at depth in Callisto makes
this possible (McKinnon 1997).
The only other significant difference between these
bodies is their orbital distances. Ganymede orbits
Jupiter at a distance of 15 Jupiter radii and Callisto
at 26.4 radii. It is unlikely these bodies formed around
Jupiter in a gravitational locked state and near circular
orbits, or that the Laplace orbital harmonic existed
between Ganymede, Europa, and Io at that time. A
particularly effective form of tidal heating of
satellites occurs around massive bodies due to orbital
eccentricity. The intensity of this tidal heating is
calculated as the square of the orbital eccentricity
(always less than one), but inversely as a large power
of the satellite's orbital distance.
One can only hypothesize the slightly different
composition and tidal dynamics of Ganymede, allowed
the process of chemical differentiation to begin in
Ganymede. It is likely once this process of
differentiation started, it would inevitably run to
its conclusion. Callisto with its slightly different
composition and orbital environment, remained
homogeneous.
A possible evolutionary scenario for Ganymede,
is that soon after accretion Ganymede underwent chemical


differentiation initiated by various mechanisms.
Ganymede would soon come to have a predominately iron
molten core surrounded by a silicate mantle, both
undergoing convection. It also probably had a global
ocean similar to Europa's. As Ganymede rotated relative
to Jupiter at this time, it could have generated a
significant magnetic field through a self-exciting
dynamo driven CLOP process.
Eventually Ganymede achieved a nearly circular
and gravitational locked orbit with Jupiter, its
internally generated magnetic field would gradually
weaken and cease. As Ganymede continued to cool, the
inner core would grow, freezing most of the outer core
and leaving a eutectic melt at the base of the mantle.
Convection in the mantle would also slowly cease and
Ganymede would become a tectonically dead object.
The global ocean would slowly freeze as well and
produce ice phases denser than water at great depth.
This shrinkage would cause extensive fracturing of the
darker terrain, which has been observed (Greeley 1994).
Whether the ocean would freeze down to the mantle surface
is uncertain, some calculations indicate the ocean would
not fully freeze (McKinnon 1997).
At around a billion years ago, a new phase in the
geologic history of Ganymede evidently began. The
interior of Ganymede undergoes a significant burst of
heating, by an unknown mechanism through the orbital
dynamics which brought Ganymede into the Laplace orbital
system with Io and Europa.
This burst of heat would cause a molten outer core
to once again form from the eutectic melt and produce
a magnetic field through a dynamo process. The mantle
72


heats up as well and starts convecting, heating any
possible ocean and heavy ice phases overlying it. As
these ice phases are denser than liquid water, their
melting would expand the body and ice slushes would
rise through pre-existing fractures to form the lighter
parallel ridged terrain of Ganymede.
This process must have continued for a while, as
around 60% of the surface of Ganymede is the lighter
parallel ridged terrain. Significant subduction and
convection of Ganymede's ice covering is highly likely.
Eventually the amount of heat evolved in the interior
slowed down and dissipated, as there is little evidence
of current surface modification of Ganymede. Heat
generated by the Laplace tidal flexing in the interior
of Ganymede and perhaps a CLOP process has been
sufficient to maintain a significant dyhamo produced
magnetic field up to the present era.
5.6 Callisto
Callisto shows little evidence of internally
generated geological activity from an examination of
its dark surface. The variations of height topography
on the surface of Callisto is more varied than Ganymede
and Europa. This is thought due to an earlier forming
and thicker lithosphere on Callisto (Greeley 1994).
The moment of inertia of Callisto is somewhat in
dispute, due to noise in the signal and manner in which
the Galileo orbiter passed Callisto. Three passes of
Callisto by Galileo have led to the measurements of
0.407 0.039, 0.412 0.044, and 0.358 0.004 for the
moment of inertia (Anderson 1998). Although a moment
of inertia of 0.4 is the ideal measurement of a sphere
73


of homogeneous composition, due to the higher density
phases of ice under pressure, a moment of inertia of
0.38 would be produced by a homogeneous Callisto
(Anderson 1998). Callisto is estimated to consist of
a homogenous mix of 45/55 rock to ice ratio (McKinnon
1997).
Obviously a moment of inertia number of greater
than 0.4 as occurred in the first two measurement is
highly unlikely. However, these values fall well within
the bounds of their uncertainty. The third measurement
of 0.358 is seen distinct evidence of differentiation
by some and its magnitude better uncertainty (0.004)
is claimed due to the ability to additionally measure
the bending and velocity perturbations along the orbital
path of Galileo (Anderson 1998).
As the surface of Callisto appears primeval,
limitations exist as to any differentiation after
accretion. A modest core of 25% the diameter of
Callisto, would melt 10% of its ice (Anderson 1998).
If such an amount of ice was generated in the interior
of Callisto, it would likely cause surface modifications
similar to the light terrain on Ganymede or rise to
the surface as granite plutons do on Earth. However,
if Callisto had a heterogeneous accretion, in which
rocky material dominated in the early stages of accretion
and ice the later, the anomalous moment of inertia figure
of 0.358 0.004 is possible.
Callisto's most significant surface feature is
the vast 4000 km diameter Valhalla multi-ringed impact
crater. The surface of Callisto appears to be blanketed
in a thin layer of dark smooth material. This dark
layer is though to be due to the loss of ice by
74


sublimation and sputtering by charged magnetic particles,
leaving behind the rocky material once bound in the
ice (McKinnon 1997).
The only internal interesting feature of Callisto
is a slight modification of Jupiter's magnetic field,
detected by the Galileo orbiter. The modification of
Jupiter's magnetic field is reminiscent of the
modification produced by Europa and suggest the
existence of a salty subsurface ocean (Kivelson 1998).
To generate the measurable field at Callisto's surface,
.the layer of water can't be too deep. Gravity maps
of Callisto estimate an icy shell of a 100 km thick
overlying this ocean (Kivelson 1998). If the ocean
was as salty as the Earth's, it would have to be
10 to 20 km deep (Kivelson 1998).
The source energy producing this ocean is
uncertain. The low eccentricity of Callisto makes
tidal forces a quite unlikely source. Radioactivity
is a bit unlikely, as it could not cause initial
differentiation and has dropped off since. One
possibility is from gravitational flexing of the
Laplace orbital system of Io, Europa, and Ganymede,
as their resonance attempts to bring Callisto into
the Laplace orbital harmonic system. Estimates of
possible global runaways in the icy shell of Ganymede,
show a breakdown of ice III into water and ice IV a
few tens of km under the surface is possible at
very low levels of tidal induced heating (Showman 1997).
It is possible a similar process in now underway on
Callisto.
75


5.7 Orbital Dynamics of the
Galilean Satellites
The three inner Galilean satellites are in a
harmonic orbital pattern called a Laplace orbital
system. For every one orbit around Jupiter by the
outermost body in the Laplace orbital system, the next
inner body completes two orbits, and Io the innermost
body completes four orbits. Callisto the most outer
Galilean satellite, is not yet a part of this Laplace
orbital harmonic system, but in the distant future it
likely will become a member as the system expands by
the transfer of angular momentum from Jupiter.
The Laplace orbital system likely came into
existence after the Galilean satellites became
gravitationally locked and achieved nearly circular
orbits around Jupiter. As Jupiter rotates faster
than the orbits of the Galilean satellites, it is
transferring angular momentum to them in the same
process as the Earth is transferring angular momentum
to the Moon. The first two bodies to achieve a Laplace
harmonic were Io and Europa. Around a billion years
ago, Ganymede became the third member of this Laplace
orbital system.
Although Jupiter is transferring significantly
more angular momentum to the innermost body Io, the
energy transfer between the bodies of the Laplace system
is much greater, ensuring the preservation of the Laplace
orbital harmonic system. This transfer of energy is
achieved by a process of tidal flexing reinforcing the
orbital harmonics. Overall in the system, there is
a net transfer of Jupiter induced angular momentum from
Io and Europa to Ganymede. This net transfer of energy
76


may be partially responsible for the present existence
of a magnetic field in Ganymede.
As the orbits of these three bodies of this Laplace
system expand over time, they will come to include
Callisto. The process of including another body into
a Laplace system may be energy intensive on the body
being included. As a Laplace orbital system expands
to become ever closer in harmony to the outer body to
be included in the Laplace system, it will begin to
slow the outer body down at an ever increasing rate
as it comes closer to being included in the Laplace
system. This process of orbital braking likely
undershoots the proper Laplace orbital harmonic.
This would then be followed by an accelerating
force to bring the body back up into the proper
Laplace orbit.
This acceleration process is likely to be
imperfect as well, and a state of ever decreasing
oscillations around the proper Laplace orbit ensues.
This oscillatory process of Laplace orbital inclusion
would likely produce intense tidal flexing and induce
significant heat into the body being included in the
Laplace orbital system.
This process of inclusion was likely to be
responsible for the reheating the interior of Ganymede
and perhaps the current generation of the subsurface
ocean in Callisto. The heat burst of Europa becoming
a member of the Laplace system is likely responsible
for its lack if ice/water relative to Ganymede and
Callisto. Any ice on Io would have long ago been
evaporated by its intense volcanic activity.
77


5.8 CLOP Interaction in a Laplace
Orbital System
The bodies of a Laplace orbital system, although
capable of transferring energy through tidal flexing,
are not able to produce a CLOP process between
themselves. These bodies orbital rotational
synchronicity with Jupiter and the orbital harmonic
ratios between each other (1-2-4), causes an oscillatory
resonance, which makes any CLOP distortion incapable
of significant differential inner core rotation. Europa
like Io, is likely to have most internal heat produced
by tidal flexing in its mantle and any generated core
heat would have its associated convecting currents
suppressed.
The Laplace CLOP process can be visualized in
Figure 7 through the two lines drawn from the equatorial
sides of Jupiter to the equatorial sides of the
satellite. The gravitational influence of Jupiter
dominates on any outer satellite influencing an inner
satellite of the Laplace system due to orbital harmonics
As all the Galilean satellites are in virtually circular
orbits, eccentricities can be ignored. The ratio of
the diameter of Jupiter to the orbit of Io is 1/2.95,
the orbit of Europa is 1/4.7, to the orbit of Ganymede
is 1/7.5 and Callisto's orbital ratio is 1/13.2.
When a satellite passes on the inside of another
satellite, the angle of action for any distortion to
be acted on the inner satellite is larger. For Ganymede
when Europa and Io pass on the inside, only one major
and two minor configurations of alignment are possible.
Any wide angle action on a distortion in Europa by
Ganymede in one alignment configuration is likely
78


Note: The potential angle foi a CLOP process is greater
on the inner satellite than the outer satellite.
cn
r-
(Orbital distances scaled to aproximate Jupiter diameters )
Jupiter
lo
Europe
Ganymede
Callisto


canceled by the triple alignment with Io and Ganymede
in the other.
Io has two maximum alignment configurations, one
with Europa and the triple alignment. However, due
to the intense internal heat likely making its core
entirely molten, no CLOP process is possible. As
Callisto is likely undifferentiated, no CLOP process
is possible there. CLOP processes in the Jovian Laplace
orbital system appear to be somewhat dependent on
circumstance.
The CLOP processes on Mercury and the Earth have
all 360 of rotation for the asymmetrical distortion
to be acted upon. The angle for the Ganymede/Callisto
is not so large at close approach, but as it does not
exist in an orbital harmonic relationship other tidal
interactions are possible. These disharmonic orbital
encounters allows Ganymede to experience a unique CLOP
interaction as Ganymede acts as a representative of
all the Laplace orbital satellites in its interaction
with Callisto.
It is only on the outside of a Laplace orbital
system, while bringing in a disharmonic significant
body, that conditions for the generation of a CLOP
process exist and in the most outer body of the Laplace
orbital system, as it acts as a representative of all
the Laplace bodies. This is seen in Ganymede currently
having a dynamo generated magnetic field, while Europa
and Io presently do not have one. The gravitational
distortion produced by disharmonic orbit of Callisto
on the inner core of Ganymede, the outermost body of
the Laplace system, may produce the asymmetry necessary
to cause the differential core rotation for a dynamo
80


produced magnetic field. This existing Laplace orbital
situation also brings up the unresolved question of
if a CLOP is necessary to produce an internally generated
magnetic field in a terrestrial object.
It is likely Io had a dynamo produced magnetic
field, while bringing Europa into a Laplace orbital
system. Once Europa became part of a Laplace system,
Io would lose its dynamo produced magnetic field.
However, Europa would start generating a dynamo produced
magnetic field as it brought Ganymede into the Laplace
system. Once Ganymede became part of the Laplace system,
Europa would lose its magnetic field. Currently,
Ganymede has a dynamo generated magnetic field, as it
brings Callisto into the Laplace orbital system.
Unfortunately, once Callisto becomes a member of
the Galilean Laplace system, it will not be able to
generate a dynamo produced magnetic field by a CLOP
process, as it is chemically undifferentiated and there
are no significant other outer bodies for it to be acted
upon. However, the bringing of a body into a Laplace
orbital harmonic system appears to generate a burst
of heat. Perhaps, enough heat will be generated to
cause the chemical differentiation of Callisto and
eventually generate a dynamo produced magnetic field
for a geologically short period of time.
81


Conclusion
The CLOP hypothesis on the retention of magnetic
fields in terrestrial objects through gravitational
distortions produced by a close large orbital partner
on the inner core of a rotating terrestrial object
encased in a molten outer core, has some support from
our current understanding of terrestrial objects.
The concept of the self-exciting dynamo being sustained
over the long term by the transfer of angular momentum
into the inner cores of these bodies from the encasing
outer regions of the planet through the effects of a
close large orbital partner is also in the realm of
mathematical possibility. Although the estimated
efficiency of the CLOP process is higher than
hypothesized, this may change as the accuracy
of the data used in the calculations improves
through further research.
CLOP hypothesis in contrast to more traditional
hypotheses, can help explain the source of the magnetic
fields in the smaller terrestrial objects of Mercury
and Ganymede. It may also help explain the tectonic
differences between the inner planets, especially
the differences between the Earth and Venus. A better
understanding of the Galilean satellites may also be
generated through an understanding of the CLOP
process.
82


The CLOP hypothesis opens up new vistas on the
understanding of core dynamics in terrestrial objects.
The asymmetrical distortion of the inner core produced
by the CLOP and the resulting transfer of angular
momentum from the encasing planet to the inner core
can help explain a significant proportion of the
unaccounted for core heat from Earth's history.
Increased understanding of the differential rotation
of the Earth's inner core and the fluid dynamics in
the outer core can be gained, as the process by which
the increased angular momentum of the inner core is
dissipated by currents and friction at the inner/outer
core boundary is researched in greater detail.
83


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