Satellites Of The Solar System Research Articles

Deformation patterns of icy satellite crusts: Insights for tectonic balancing and fluid migration through structural analysis of terrestrial analogues

The icy satellites of the Solar System, such as Europa and Ganymede, show widespread evidence for tectonic structures that provide insights to infer the kinematics and the mechanical properties of their crusts. Their investigation is pivotal for the understanding of the regimes responsible for their formation and the connection with subsurface layers. Icy satellite tectonics is dominated by extension and shear regimes, while paucity evidence for compression represents an open issue. Structural investigation is constrained at regional-scale coverage of the remote sensing imagery. The study of analogues on Earth represents a strong support for the geologic analysis of the icy satellites. Glaciers represent optimal terrestrial analogues, showing deformation styles at multiple scale similar to those in the icy satellites, and being the excellent sites to further explore, verify and confirm what observed through remote sensing on the icy satellite geology. Although the formation processes differ, the similarity of their structures at surface allows quantifying and predicting the state of deformation in the icy satellites at different scales of investigation. Moreover, glacier deformation shows corridor-like pattern (i.e., shear zone with internal associated deformation), analogous to the main tectonic setting recognized in the icy satellites. This work aims to investigate and compare the tectonic structures of the glaciers with those on the icy satellites, by means of multi-scale approach of both remote-sensing and field survey. We present a structural investigation in the Russell and Isunguata Sermia glaciers, located at the western margin of the Greenland Ice Sheet, where field campaign has been conducted by the UPSIDES project under the Europlanet 2024 RI's Transnational Access field analogue in Kangerlussuaq. This project aims i) to achieve knowledge of the ice tectonic setting at local-scale, ii) to compare with that at regional-scale, and in turn iii) to better understand the tectonic styles and to characterize structures that are exclusively identified at regional-scale (such as in the icy satellites). Field measurements of brittle structures (fractures/faults), concerning the quantification of their azimuth, dip, length, width, throw and spacing, have been performed. In parallel, remote sensing analysis, concerning structural mapping on areas including the locations of the investigated outcrops, allowed to derive the same quantities at regional-scale. In this way, both local- and regional-scale tectonic setting has been investigated, and the stress analysis has been performed. Obtained results have been compared and in turn related with areas that show similar tectonic setting on Ganymede. In particular, the lack of detection of the regional-scale counterpart of the low-angle structures, and in particular the compressional ones that have been recognized at local-scale in the investigated glaciers, has been related to the lack of evidence of such structures in the icy satellite's surfaces. Such comparison allows us to infer a tectonic model that accounts for the existence of deep zones of balanced deformation depicted by diffuse and low-angle structures, and can explain their limited detection at surface and regional-scale investigations.

Interplanetary transfers using stable and unstable manifold tubes originating at [formula omitted] and [formula omitted] in the elliptic restricted three-body problems

The solutions originating at the Lagrangian points L1 and L2 of the restricted three-body problem are used in space flight dynamics to find useful station-keeping orbits as well as convenient low-energy transfers between planets and satellites of the Solar System. The circular restricted three-body problem (CR3BP) provides the simplest model where the Lagrangian points, as well as the related stable and unstable manifold tubes, are defined. Nevertheless, their use for Solar System applications requires to consider hierarchical extensions of the model. The elliptic restricted three-body problem (ER3BP) is the most important extension to consider for space flight dynamics. In this paper we discuss the differences of the manifold tubes of the ER3BP with respect to the CR3BP which have an impact in the transfers between orbits in the manifold tubes related to different planets. We find that there is a threshold value for the eccentricity of the planet, depending on its reduced mass, which changes drastically the distribution of the longitudes of the first pericenter (or apocenter) of the orbits in the manifold tubes leaving or approaching the Lagrangian points L1, L2. For example, such a difference changes the design of the Hohmann transfers between two orbits of the manifold tubes when the planets Mercury or Mars are concerned.

X-ray diffraction reveals two structural transitions in szomolnokite

AbstractHydrated sulfates have been identified and studied in a wide variety of environments on Earth, Mars, and the icy satellites of the solar system. The subsurface presence of hydrous sulfur-bearing phases to any extent necessitates a better understanding of their thermodynamic and elastic properties at pressure. End-member experimental and computational data are lacking and are needed to accurately model hydrous, sulfur-bearing planetary interiors. In this work, high-pressure X-ray diffraction (XRD) and synchrotron Fourier-transform infrared (FTIR) measurements were conducted on szomolnokite (FeSO4·H2O) up to ~83 and 24 GPa, respectively. This study finds a monoclinic-triclinic (C2/c to P1) structural phase transition occurring in szomolnokite between 5.0(1) and 6.6(1) GPa and a previously unknown triclinic-monoclinic (P1 to P21) structural transition occurring between 12.7(3) and 16.8(3) GPa. The high-pressure transition was identified by the appearance of distinct reflections in the XRD patterns that cannot be attributed to a second phase related to the dissociation of the P1 phase, and it is further characterized by increased H2O bonding within the structure. We fit third-order Birch-Murnaghan equations of state for each of the three phases identified in our data and refit published data to compare the elastic parameters of szomolnokite, kieserite (MgSO4·H2O), and blödite (Na2Mg(SO4)2·4H2O). At ambient pressure, szomolnokite is less compressible than blödite and more than kieserite, but by 7 GPa both szomolnokite and kieserite have approximately the same bulk modulus, while blödite’s remains lower than both phases up to 20 GPa. These results indicate the stability of szomolnokite’s high-pressure monoclinic phase and the retention of water within the structure up to pressures found in planetary deep interiors.

Excitation, emission, and synchronous fluorescence for astrochemical applications: Experiments and computer simulations of synchronous spectra of polycyclic aromatic hydrocarbons and their mixtures

Synchronous fluorescence spectroscopy is a variation of the fluorescence technique for detection and characterization of many single ring aromatic organic molecules, polycyclic aromatic hydrocarbons, and fluorescent amino acids among other molecules. To our knowledge this technique has not been used in space exploration. In order to demonstrate the utility of this technique for planetary and astrochemical applications, we present several laboratory experiments and computer simulations with pure samples and mixtures. Computer deconvolution of experimental excitation and emission fluorescence bands is presented and used to generate synchronous spectra. The computer simulation successfully predicts the number of synchronous fluorescence (SF) bands, band shapes, and band maximum wavelengths for any constant wavelength difference (Δλ). To test the simulation, emission, excitation, and synchronous spectra were obtained for anthracene in n-hexane. Excellent agreement is obtained reproducing and finding the origin of the experimental SF bands for values of Δλ between 2 and 100. The excitation, emission, and synchronous (Δλ = 10) spectra of toluene, aniline, naphthalene, acenaphthene, pyrene, and anthracene are obtained. Excitation of a mixture of the six compunds at three wavelengths (249, 266, and 355 nm) produce fluorescence emission spectra identifying some compounds. The synchronous spectrum (Δλ = 10) of the same mixture is presented and assigned based on the synchronous bands of the individual compounds. The synchronous fluorescence technique and the computer simulation method are proposed to complement other techniques in the analysis of fluorescent samples from comets, as well as in missions to planets and satellites of the solar system.

Polarimetry of Water Ice Particles Providing Insights on Grain Size and Degree of Sintering on Icy Planetary Surfaces

AbstractThe polarimetry of the light scattered by planetary surfaces is a powerful tool to provide constraints on their microstructure. To improve the interpretation of polarimetric data from icy surfaces, we have developed the POLarimeter for ICE Samples complementing the measurement facilities of the Ice Laboratory at the University of Bern. The new setup uses a high precision Stokes polarimeter to measure the degree of polarization in the visible light scattered by surfaces at moderate phase angles (from 1.5° to 30°). We present the photometric and polarimetric phase curves measured on various surfaces made of pure water ice particles having well‐controlled size and shape (spherical, crushed, and frost). The results show how the amplitude and the shape of the negative polarization branch change with the particles sizes and the degree of metamorphism of the ice. We found that fresh frost formed by water condensation on cold surfaces has a phase curve characterized by resonances (Mie oscillations) indicating that frost embryos are transparent micrometer‐sized particles with a narrow size distribution and spherical shape. Comparisons of these measurements with polarimetric observations of the icy satellites of the Solar System suggest that Europa is possibly covered by relatively coarser (~40–400 μm) and more sintered grains than Enceladus and Rhea, more likely covered by frost‐like particles of few micrometers in average. The great sensitivity of polarization to grain size and degree of sintering makes it an ideal tool to detect hints of ongoing processes on icy planetary surfaces, such as cryovolcanism.

Geo-cosmic Universal X-structure of Solar System Planets and Satellites in Applying to Exoplanet Systems

Given a new unique method of calculating satellite systems approved at all, without exception, 185 satellites of the Solar system. The base of the Geo-cosmic Universal X-structure of Solar system planets and satellites represents a discrete-continuous distribution of satellite and longest rings in axes the density/orbital radius (semi-major axis of the orbit), converted to the scale of the central body. Previously, it was found that in all cases, the maximum radius of the rings is the same as the triple radius of the central body for the border zones of destructive tidal actions with 12% spread. For Pluto's radius 1184 km radius of rings on X-structure may range from 4000 to 7000 km. It was far enough away from 12000 km radius of passage of spacecraft "New horizons". The success of the application of the method of the X-structure is shown here. For some exoplanets within 50 light-years (15pc) of the Earth by a method of the Geo-cosmic universal X-structure it is studied questions of the definition of the exoplanets parameters: density-diameter etc. Given also the Universal Geo-cosmic X-structure theoretical Levels of the similarity of natural satellites of the Solar system planets. Comparative characteristics between the method of the X-structure on the one hand and the modification of the Lunar systems Titius-Bode law оn the other hand given in Appendix A. From the theory, in particularly, follows the mystery similarity between the Mercury and the Earth’s Moon. Study of this layer of the undoubted new reality held in Appendix B. On pictures of the surface of Pluto and Charon the crust thickness was determined. Crust of Pluto from pole 21 km. The ice crust Charon thickness at pole is 18 km.

The theory of secondary resonances in the spin–orbit problem

We study the resonant dynamics in a simple one degree of freedom, time dependent Hamiltonian model describing spin-orbit interactions. The equations of motion admit periodic solutions associated with resonant motions, the most important being the synchronous one in which most evolved satellites of the Solar system, including the Moon, are observed. Such primary resonances can be surrounded by a chain of smaller islands which one refers to as secondary resonances. Here, we propose a novel canonical normalization procedure allowing to obtain a higher order normal form, by which we obtain analytical results on the stability of the primary resonances as well as on the bifurcation thresholds of the secondary resonances. The procedure makes use of the expansion in a parameter, called the detuning, measuring the shift from the exact secondary resonance. Also, we implement the so-called `book-keeping' method, i.e., the introduction of a suitable separation of the terms in orders of smallness in the normal form construction, which deals simultaneously with all the small parameters of the problem. Our analytical computation of the bifurcation curves is in excellent agreement with the results obtained by a numerical integration of the equations of motion, thus providing relevant information on the parameter regions where satellites can be found in a stable configuration.

Stability of rubble-pile satellites

We consider the stability of rubble-pile satellites that are held together by their own gravity. A satellite is said to be stable whenever it is both orbitally and structurally stable to both orbital and structural perturbations. We restrict attention to satellites whose dimensions are small compared to their respective orbital radii and their associated planets’ sizes. In this case, we show that a satellite is stable whenever it is orbitally stable to orbital perturbations and structurally stable to structural perturbations. Orbital stability is investigated by a spectral analysis, while structural stability is probed by appropriately extending the work of Sharma [Sharma, I., 2012. Stability of rotating non-smooth complex fluids. J. Fluid Mech. 708, 71–99; Sharma, I., 2013. Structural stability of rubble-pile asteroids. Icarus 223, 367–382]. The stability test is then applied to planetary satellites of the Solar System that are suspected to be granular aggregates, including many of the recently discovered smaller moons of the giant planets.

Phase diagram of H2O: Thermodynamic functions of the phase transitions of high-pressure ices

The analysis of the internal structure of the ice satellites of the Solar System’s giant planets, Jupiter and Saturn, and the estimation of the composition of other water-containing cosmic bodies require thermodynamic information on the phase transformations in the water-ice system. This work presents experimental and theoretical data on the studies of the phase diagram of water (H2O) and the thermodynamic properties of water ices that were generalized, analyzed, and systematized. A brief description of the equations of state for different modifications of high-pressure ices that are most frequently used in thermodynamic calculations is presented. Based on the mathematical treatment of available experimental data for phase equilibria in the water-ice system, the boundaries of the phase transitions between crystal ices I, II, III, V, VI, VII, VIII, and X and liquid water are constructed; in addition, the thermal dependences of the thermodynamic functions (changes in enthalpy, entropy, and volume) of most water-ice phase transitions are obtained.

Theory of the rotation of the Galilean satellites

AbstractAs most of the natural satellites of the Solar System, the Galilean moons are since a long time assumed to be tidally locked in a spin-orbit synchronous resonance. Thanks to the mission Galileo, we now dispose of enough gravity data to perform 3-dimensional theories of the rotation of these satellites, in particular to model the departure from the exact synchronous rotation. We here present such theories depending on the interior model we consider, in highlighting some observable output data. Inverting them will give us information on the internal structure of these bodies.

Expression of Cassini's third law for Callisto, and theory of its rotation

The rotation of the main natural satellites of the Solar System is widely assumed to be synchronous, because this corresponds to an equilibrium state. In the case of the Moon, 3 laws have been formulated by Cassini, assuming a spin–orbit resonance and a 1:1 nodal resonance. The recent gravitational data collected by the spacecrafts Galileo (in the jovian system) and Cassini (in the saturnian system) allows us to study the rotation of other natural satellites, and to check the universality of Cassini's laws. This paper deals with the rotation of the Galilean satellites of Jupiter J-4 Callisto. In this study we use both analytical (like Lie transforms) and numerical methods (numerical detection of chaos, numerical integration, frequency analysis) to first check the reliability of Cassini Laws for Callisto, and then to give a first theory of its rotation, Callisto's being considered as a rigid body. We first show that the Third Cassini Law (i.e. the nodal resonance), is not satisfied in every reference frame, in particular in the most natural one (i.e. the J2000 jovian equator). The difference of the nodes presents a chaotic-like behavior, that we prove to be just a geometrical illusion. Moreover, we give a mathematical condition ruling the choice of an inertial reference frame in which the Third Cassini Law is fulfilled. Secondly, we give a theory of Callisto's rotation in the International Celestial Reference Frame (ICRF). We highlight a small motion (i.e. <200 m) of its rotation axis about its body figure, a 11.86-yr periodicity in Callisto's length-of-day, and the proximity of a resonance that forces 182-yr librations in Callisto's obliquity.

Tidal disruptions: II. A continuum theory for solid bodies with strength, with applications to the Solar System

We present a comprehensive theory for the breakup conditions for ellipsoidal homogeneous secondary bodies subjected to the tidal forces from a nearby larger primary: for materials ranging from purely fluid ones, to granular rubble-pile gravel-like ones, and to those with either cohesive or granular strength including cohesive rocks and metals. The theory includes but greatly extends the classical analyses given by Roche in 1847, which dealt only with fluids, and also our previous analysis [Holsapple, K.A., Michel, P., 2006. Icarus 183, 331–348], which dealt only with solid but non-cohesive bodies. The results here give the distance inside of which breakup must occur, for both a steadily orbiting satellite and for a passing or impacting object. For the fluid bodies there is a single specific shape (a “Roche Ellipsoid”) that can be in equilibrium at any given distance from a primary, and especially only one shape that can exist at the overall minimum distance ( d / R ) ( ρ / ρ p ) 1 / 3 = 2.455 , the classical well-known “Roche limit.” In contrast, solid bodies can exist at a given distance from a primary with a range of shapes. Here we give multiple plots of the minimum distances for various important combinations of body shape, spin, mass density, and the strength parameters characterized by an angle of friction and cohesive strength. Such results can be used in different ways. They can be used to estimate limits on strengths and mass densities for orbiting bodies at a known distance and shape. They can be used to determine breakup distances for passing bodies with an assumed strength and shape. They can be used to constraint physical properties such as bulk density of bodies with a known shape that were known to breakup at a given distance. A collection of approximately 40 satellites of the Solar System is used for comparison to the theory. About half of those bodies are closer than the Roche fluid limit and must have some cohesion and/or friction angle to exist at their present orbital distance. The required solid strength for those states is determined. Finally, we apply the theory to the break up of the SL9 comet at close approach with Jupiter. Our results make clear that the literature estimates of its bulk density depend markedly on unknown parameters such as shape, orientation and spin, and most importantly, material strength characterization.

Mass–radius curve for extrasolar Earth-like planets and ocean planets

By comparison with the Earth-like planets and the large icy satellites of the Solar System, one can model the internal structure of extrasolar planets. The input parameters are the composition of the star (Fe/Si and Mg/Si), the Mg content of the mantle (Mg# = Mg/[Mg + Fe]), the amount of H 2O and the total mass of the planet. Equation of State (EoS) of the different materials that are likely to be present within such planets have been obtained thanks to recent progress in high-pressure experiments. They are used to compute the planetary radius as a function of the total mass. Based on accretion models and data on planetary differentiation, the internal structure is likely to consist of an iron-rich core, a silicate mantle and an outer silicate crust resulting from magma formation in the mantle. The amount of H 2O and the surface temperature control the possibility for these planets to harbor an ocean. In preparation to the interpretation of the forthcoming data from the CNES led CoRoT (Convection Rotation and Transit) mission and from ground-based observations, this paper investigates the relationship between radius and mass. If H 2O is not an important component (less than 0.1%) of the total mass of the planet, then a relation ( R / R Earth ) = a ( M / M Earth ) b is calculated with ( a , b ) = ( 1 , 0.306 ) and ( a , b ) = ( 1 , 0.274 ) for 10 −2 M Earth < M < M Earth and M Earth < M < 10 M Earth , respectively. Calculations for a planet that contains 50% H 2O suggest that the radius would be more than 25% larger than that based on the Earth-like model, with ( a , b ) = ( 1.258 , 0.302 ) for 10 −2 M Earth < M < M Earth and ( a , b ) = ( 1.262 , 0.275 ) for M Earth < M < 10 M Earth , respectively. For a surface temperature of 300 K, the thickness of the ocean varies from 150 to 50 km for planets 1 to 10 times the Earth's mass, respectively. Application of this algorithm to bodies of the Solar System provides not only a good fit to most terrestrial planets and large icy satellites, but also insights for discussing future observations of exoplanets.

The shapes and rotational dynamics of minor planetary satellites

Statistical analysis of the available data on the sizes and inertial parameters for all hitherto known satellites of the Solar system’s planets is performed. Analytical approximations are derived for the size distribution of satellites. Empirical relations are obtained to approximately estimate the inertial parameters of a satellite from its size. These relations can be used in statistical studies of the possibility of manifestations of various nonstandard rotational modes of planetary satellites. In particular, the probability of the “Amalthea effect” (the presence of two centers of synchronous resonance in the phase space of rotational motion) is shown to be much higher for minor (with diameters smaller than 100 km) satellites moving in close-to-circular orbits than for other satellites.

Tidal disruptions: A continuum theory for solid bodies

Although the theory of Roche 1847 for the tidal disruption limits of orbiting satellites assumes a fluid body, a length to diameter of exactly 2.07:1, and a particular body orientation, the theory is commonly applied to the satellites of the Solar System and to small asteroids and comets passing nearby a planet. Clearly these bodies are neither fluid nor generally are that elongated, so a more appropriate theory is needed. Here we present exact analytical results for the distortion and disruption limits of solid spinning ellipsoidal bodies subjected to tidal forces, using the Drucker–Prager strength model with zero cohesion. It is the appropriate model for dry granular materials such as sands and rocks, for rubble-pile asteroids and comets, and for larger satellites, asteroids and comets where the cohesion can be ignored. This study uses the same approach as the studies of spin limits for solid ellipsoidal bodies given in [Holsapple, K.A., 2001. Icarus 154, 432–448; Holsapple, K.A., 2004. Icarus 172, 272–303]. It is a static theory that predicts conditions for breakup and predicts the nature of the deformations at the limit state, but does not track the dynamics of the body as it comes apart. The strength is characterized by a single material parameter associated with an angle of friction, which can range from zero to 90°. The case with zero friction angle has no shear strength whatsoever, so it is then the model of a fluid or gas. The case of 90° represents a material that cannot fail in shear, but still has zero tensile strength. Typical dry soils have angles of friction of 30°–40°. Since the static fluid case is included in the theory as a special case, the classical results of Roche [Roche, E.A., 1847. Acad. Sci. Lett. Montpelier. Mem. Section Sci. 1, 243–262] and Jeans [Jeans, J.H., 1917. Mem. R. Astron. Soc. London 62, 1–48] are included and re-derived in their entirety; but the general solid case has much more variety and applicability. We consider both the spin-locked case, appropriate for most satellites of the Solar System; and the zero spin case, a possible case for a passing stray body. Detailed plots of many special cases are presented, in terms of shape, orientation and mass densities. A very typical result gives a closest approach d = 1.5 ( ρ / ρ P ) 1 / 3 R in terms of the planet radius R, and the satellite and planet mass densities ρ and ρ P . We also use the theory to distinguish between conditions allowing global shape changes leading to new equilibrium states, or those leading to complete disruption. We apply the theory to the potentially hazardous Asteroid 99942 Apophis due to pass very near the Earth in 2029, and conclude it is extremely unlikely to experience any tidal readjustments during its passage. The states of many of the satellites of the Solar System are compared to the theory, and we find that all are well within their tidal disruption limits for expected values of the internal friction.

Third-Body Perturbation in Orbits Around Natural Satellites

An analytical and a numerical study of the perturbation imparted to a spacecraft by a third body is developed. There are several important applications of the present research, such as calculation of the effect of lunar and solar perturbations on high-altitude Earth satellites. The goal is to study the evolution of orbits around some important natural satellites of the solar system, such as the moon, the Galilean satellites of Jupiter, Titan, Titania, Triton, and Charon. There is special interest in learning under which conditions a near-circular orbit remains near circular. The existence of circular, equatorial, and frozen orbits are also considered for a lunar satellite, but the results are valid for any system of primaries by making a time transformation that depends on the masses of the bodies involved. Several plots will show the time histories of the Keplerian elements of the orbits involved. Then, a study is performed to estimate the lifetime of orbits around those natural satellites.

Tables of Libration-Point Parameters for Selected Solar System Objects

This report documents the currently-recognized most accurate values for the masses, radii, and certain mean orbital elements for the major planets, the asteroid (433) Eros, and many of the satellites of the Solar System. These values were used to produce computer-generated tables of libration-point parameters.

Extraterrestrial organic chemistry: from the interstellar medium to the origins of life. Part 2: complex organic chemistry in the environment of planets and satellites.

During COSPAR'00 in Warsaw, Poland, in the frame of Sub-Commission F.3 events (Planetary Biology and Origins of Life), part of COSPAR Commission F (Life Sciences as Related to Space), and Commission B events (Space Studies of the Earth-Moon System, Planets, and Small Bodies of the Solar System) a large joint symposium (F.3.4/B0.8) was held on extraterrestrial organic chemistry. Part 2 of this symposium was devoted to complex organic chemistry in the environment of planets and satellites. The aim of this event was to cover and review new data which have been recently obtained and to give new insights on data which are expected in the near future to increase our knowledge of the complex organic chemistry occurring in several planets and satellites of the Solar System, outside the earth, and their implications for exobiology and life in the universe. The event was composed of two main parts. The first part was mainly devoted to the inner planets and Europa and the search for signatures of life or organics in those environments. The second part was related to the study of the outer solar system.

Growth of planetary crusts

The planets and satellites of the Solar System show much diversity, but most have formed crusts which differ substantially from their bulk compositions. Three principal types of crust may be broadly distinguished: primary, formed after accretional heating (e.g., lunar highlands); secondary, formed following partial melting in planetary mantles (e.g., lunar maria, terrestrial oceanic crust); and tertiary, formed by processing of secondary crusts, of which the continental crust of the Earth is the only identifiable example. Crustal growth before 3800 m.y. was complicated by the heavy planetesimal bombardment: active erosion on the Earth is likely to have destroyed the brecciated rubble resulting from over 200 Mare Orientale-scale events in this period. The Mercurian crust is probably primary, perhaps analogous to the lunar highlands. In contrast, the observable Martian and Venusian crusts are secondary, dominated by basaltic volcanism. The icy crusts of the satellites of the outer planets are mixtures of both primary and secondary crusts, with complex histories. Ganymede is of special interest in displaying a secondary (grooved terrain) water ice crust which has split an older more heavily cratered, possibly primary crust. Slight expansion has resulted probably from polymorphic transitions from high density ice VIII to low density ice I. The primary lunar crust, 12% of lunar volume, grew in 10 8 years; secondary crusts derived by partial melting of mantles grow at a much slower rate—total production of terrestrial oceanic crust over 4000 m.y. is only 2% of planetary volume, whereas terrestrial continental crustal growth is even slower, producing over the same period a volume only about 0.33% that of the Earth. Crustal growth on the other planets appears to be an irreversible process, without evidence of recycling. No evidence for massive planetary expansion, as required by expanding earth hypotheses, is apparent on the other planets or satellites of the Solar System.

Physics of Planetary Interiors

Our knowledge of the planets and the satellites of the Solar System has grown enormously particularly due to the stimulus from space missions. Studies of the interiors, atmospheres and interplanetary regions have all benefited from these developments. The result has been an increase in our understanding of the general workings of the planets and satellites and relative planetology has become an active area of quantitative study. These aspects are likely to develop significantly in the future and the effects on our appreciation of the Earth itself will be very significant. Conditions within the interiors of the planets and larger satellites are reviewed in the present paper against the more general background of the physics to be expected for a planetary body in general. No other planetary system has yet been discovered for comparative study so our Sun with its group of planets and satellites remains to us unique.