Planetary observations at a wavelength of 1.32 mm

Observations at a wavelength of 1.32 mm have been made of the Jovian planets, Ceres, the satellites Callisto and Ganymede, and the HII region DR 21. The observed brightness temperatures are presented. Those of the Jovian planets agree with the values expected from model atmosphere calculations, except that of Jupiter, which is lower than expected. Ceres and the satellites do not have atmospheres so their emission arised in their subsurface layers. The observed brightness temperatures are intermediate between those measured at infrared and centimeter wavelengths.     

Comments on a global polytropic model for the

By comparing the predictions of a global polytropic model (developed by the first author) for the Solar and Jovian systems with other models and observational data it is shown that, even though this model has a minimal input, it produces interesting results concerning the masses and distances of planets and satellites.     

Determination of the masses of planetary satellites from their mutual gravitational perturbations

We analyze the possibility of determining the masses of outer planetary satellites from their mutual gravitational perturbations via ground-based observations. Such a technique has been applied in (Emelyanov, 2005b) to determine the mass of the Jovian satellite Himalia. In this paper, we use the least-squares method to compute the errors of satellite masses inferred from simulated observations. We analyze several of the most suitable variants of groups of outer satellites of planets with maximum mutual attraction. We found that the mass of the Satumian satellite Phoebe (S9) can be refined by continuing observations of the satellite S25 Mundilfari until 2027. We show that the masses of other known outer planetary satellites cannot be determined from ground-based observations.     

Inferred heat transfer mechanisms and tectonic development of planets and satellites

A schematic diagram showing the relative importance of conduction, convection and hotspots as heat transfer mechanisms on planets has been previously described by Solomon and Head (1982). In their construction they assumed that the majority of heat transfer on Earth involved mantle convection (and hence, plate recycling), with Io and Mercury dominated by hotspot and conduction, respectively. This diagram is here quantified and used to deduce the tectonic regime of Jovian and Saturnian satellites.     

Modelling the proto-Jovian atmospheres by a simple analytical algorithm

This paper models the proto-Jovian atmospheres by a simple analytical algorithm, which does not require the use of a computer. This method, known as the MDV method, was used to model the present structures of the Jovian planets in Doorish (1992). The protoplanetary stages of the Jovian planets, known as stage 1 of development, can be described by the Stellar Interior Equations (SIE). These equations which basically dictate the structure of a star, can also be used to model the Jovian planets (Bodenheimer, 1986). We here include tabulated results.     

Imaging planets around nearby white dwarfs

We suggest that Jovian planets will survive the late stages of stellar evolution, and that white dwarfs will retain planetary systems in wide orbits (≳5 au). Utilizing evolutionary models for Jovian planets, we show that infrared imaging with 8-m class telescopes of suitable nearby white dwarfs should allow us to resolve and detect companions ≳3 M _JUP. Detection of massive planetary companions to nearby white dwarfs would prove that such objects can survive the final stages of stellar evolution, place constraints on the frequency of main-sequence stars with planetary systems dynamically similar to our own and allow direct spectroscopic investigation of their composition and structure.     

Occurrence of central peak craters on the Saturnian satellites: Implications for surface structure

The presence of craters with central peaks on the ice satellites of Saturn implies that their surface elastic strength is comparable to that of the Moon, Mars, and Mercury which have central peak craters, rather than that of the Jovian ice satellites Ganymede and Callisto which do not have central peak craters.     

Some dynamical aspects of the accretion of Uranus and Neptune: The exchange of orbital angular momentum with planetesimals

The final stage of the accretion of Uranus and Neptune is numerically investigated. The four Jovian planets are considered with Jupiter and Saturn assumed to have reached their present sizes, whereas Uranus and Neptune are taken with initial masses 0.2 of their present ones. Allowance is made for the orbital variation of the Jovian planets due to the exchange of angular momentum with interacting bodies (“planetesimals”). Two possible effects that may have contributed to the accretion of Uranus and Neptune are incorporated in our model: (1) an enlarged cross section for accretion of incoming planetesimals due to the presence of extended gaseous envelopes and/or circumplanetary swarms of bodies; and (2) intermediate protoplanets in mid-range orbits between the Jovian planets. Significant radial displacements are found for Uranus and Neptune during their accretion and scattering of planetesimals. The orbital angular momentum budgets of Neptune, Uranus, and Saturn turn out to be positive; i.e., they on average gain orbital angular momentum in their interactions with planetesimals and hence they are displaced outwardly. Instead, Jupiter as the main ejector of bodies loses orbital angular momentum so it moves sunward. The gravitational stirring of planetesimals caused by the introduction of intermediate protoplanets has the effect that additional solid matter is injected into the accretion zones of Uranus and Neptune. For moderate enlargements of the radius of the accretion cross section (2–4 times), the accretion time scale of Uranus and Neptune are found to be a few 10⁸ years and the initial amount of solid material required to form them of a few times their present masses. Given the crucial role played by the size of the accretion cross section, questions as to when Uranus and Neptune acquired their gaseous envelopes, when the envelopes collapsed onto the solid cores, and how massive they were are essential in defining the efficiency and time scale of accretion of the two outer Jovian planets.     

Effects of Planetary Migration on Natural Satellites of the Outer Planets

Numerous studies in the past few years have analyzed possible effects of planetary migration on the small bodies of the Solar System (mainly asteroids and KBOs), with the double aim of explaining certain dynamical structures in these systems, as well as placing limits on the magnitude of the radial migration of the planets. Here we undertake a similar aim, only this time concentrating on the dynamical stability of planetary satellites in a migration scenario. However, different from previous works, the strongest perturbations on satellite systems are not due to the secular variation of the semimajor axes of the planets, but from the planetesimals themselves. These perturbations result from close approaches between the planetesimals and satellites.We present results of several numerical simulations of the dynamical evolution of real and fictitious satellite systems around the outer planets, under the effects of multiple passages of a population of planetesimals representing the large-body component of a residual rocky disk. Assuming that this component dominated the total mass of the disk, our results show that the present systems of satellites of Uranus and Neptune do not seem to be compatible with a planetary migration larger than even one quarter that suggested by previous studies, unless these bodies were originated during the late stage of evaporation of the planetesimal disk. For larger variations of the semimajor axes of the planets, most of the satellites would either be ejected from the system or suffer mutual collisions due to excitation in their eccentricities. For the systems of Jupiter and Saturn, these perturbations are not so severe, and even large migrations do not introduce large instabilities.Nevertheless, even a small number of 1000-km planetesimals in the region may introduce significant excitation in the eccentricities and inclinations of satellites. Adequate values of this component may help explain the present dynamical distribution of distant satellites, including the highly peculiar orbit of Nereid.     

Gas drag in primordial circumplanetary envelopes: A mechanism for satellite capture

Some natural satellites may have been captured due to the gas drag they experienced in passing through primordial circumplanetary nebulas. This paper models such an encounter and derives the testable parameters from the known properties of current solar system objects and Bodenheimer's (1977, Icarus 31) model of the earliest phases of Jupiter's evolution. We propose that the clusters of prograde and retrograde irregular satellites of Jupiter originated when two parent bodies were decelerated and fragmented as they passed through an extended primordial Jovian nebula. Fragmentation occured because the gas dynamic pressure exceeded the parent bodies' strengths. These events must have occurred only shortly before the primordial nebula experienced hydrodynamical collapse so that subsequently the fragments underwent only limited orbital evolution. Because self-gravity exceeded the relative drag force, the fragments initially remained together, only to be dispersed at a later time by a collision with a stray body. Predictions of this hypothesis, such as orbital distance of the irregular satellites and size of the parent bodies, are found to be consistent with the observed properties of Jupiter's irregular satellites. In addition nebular drag at a later time may have caused the inner three Galilean satellites to undergo a modest amount of orbital evolution, accounting for their present orbital resonance. Gas drag capture of Saturn's Phoebe and Iapetus and Neptune's Nereid and Triton may also be possible. Reasonable differences in properties could explain why these satellites, in contrast to the Jovian ones, did not fracture upon capture. The current irregular satellites represent only a tiny fraction of the bodies captured by primordial nebulas. The dominant fraction would have spiraled into the center of the nebula as a result of continued gas drag and thus offer one source for the heavy element cores of the outer planets. If one is willing to postulate the presence of a massive gaseous nebula around primordial Mars, then gas drag capture could account for the origin of the Martian moons. We hypothesize that a single parent body was captured in a region of the nebula where the gas velocity approached the Keplerian value, that it fragmented upon deceleration into at least two bodies, Phobos and Deimos, and that continued nebular drag led to the low eccentricity and inclination that characterize the satellites' current orbits. Following the dissipation of this nebula, the more massive Phobos tidally evolved to its current position.     

The wave nature and dynamical quantization of the solar system

A heuristic model is proposed of the mean distances between the solar-system planets, their satellites and the primaries. The model is based on: (i) the concept of the solar system structure wave nature; (ii) the micro-mega analogy (MM analogy) of the micro- and megasystem structures, and (iii) the oscillator amplitude quantization phenomenon, occuring under wave action, discovered on the basis of the classical oscillations theory (Damgov et al., 1990, 1991).From the equation, describing the charge rotation under the action of an electromagnetic wave, an expression is obtained for the discrete set of probable stationary motion amplitudes. The discrete amplitude values — the quantization phenomenon — are defined by the argument values at the extreme points of the N-order Bessel functions. Using this expression, the mean related distances are computed from the solar system planets and the Saturn, Uranian and Jovian satellites to the primaries.     

Computer simulations of planetary accretion dynamics: Sensitivity to initial conditions

We have tested the implications and limitations of Program ACRETE, a scheme based merely on Newtonian physics and accretion with unit sticking efficiency, devised by Dole in 1970 to simulate the origin of the planets. The dependence of the results on a variety of radial and vertical density distribution laws, on the ratio of gas to dust in the solar nebula, on the total nebula mass, and on the orbital eccentricity, ?, of the accreting grains are explored. Only for a small subset of conceivable cases are planetary systems closely like our own generated. Many models have tendencies toward one of two preferred configurations: multiple-star systems, or planetary systems in which Jovian planets either have substantially smaller masses than in our system or are absent altogether. But for a wide range of cases recognizable planetary systems are generated, ranging from multiple-star systems with accompanying planets, to systems with Jovian planets at several hundred astronomical units, to single stars surrounded only by asteroids. Many systems exhibit planets like Pluto and objects of asteroidal mass, in addition to usual terrestrial and Jovian planets. No terrestrial planets were generated more massive than five Earth masses. The number of planets per system is for most cases of order 10, and, roughly, inversely proportional to ?. All systems generated obey a relation of the Titius-Bode variety for relative planetary spacing. The case with which planetary systems are generated using such elementary and incomplete physical assumptions supports the idea of abundant and morphologically diverse planetary systems throughout the Galaxy.     

Multicolor photometry of outer Jovian satellites

Multicolor photometry was obtained of satellites J6 Himalia, J7 Elara, and J10 Lysithea in the prograde cloud of outer Jovian satellites, and of J8 Pasiphae, J9 Sinope, and J11 Carme in the retrograde cloud. Our data for J9 are fragmentary; otherwise, the satellites all look like C-class asteroids, except J11, which shows a remarkable brightness in the ultraviolet. The absence of D-class spectra among the outer Jovian satellites suggests that they were not derived from the same population as the outer-belt and Trojan asteroid populations.     

LAPLACE: A mission to Europa and the Jupiter System for ESA’s Cosmic Vision Programme

The exploration of the Jovian System and its fascinating satellite Europa is one of the priorities presented in ESA’s “Cosmic Vision” strategic document. The Jovian System indeed displays many facets. It is a small planetary system in its own right, built-up out of the mixture of gas and icy material that was present in the external region of the solar nebula. Through a complex history of accretion, internal differentiation and dynamic interaction, a very unique satellite system formed, in which three of the four Galilean satellites are locked in the so-called Laplace resonance. The energy and angular momentum they exchange among themselves and with Jupiter contribute to various degrees to the internal heating sources of the satellites. Unique among these satellites, Europa is believed to shelter an ocean between its geodynamically active icy crust and its silicate mantle, one where the main conditions for habitability may be fulfilled. For this very reason, Europa is one of the best candidates for the search for life in our Solar System. So, is Europa really habitable, representing a “habitable zone” in the Jupiter system? To answer this specific question, we need a dedicated mission to Europa. But to understand in a more generic way the habitability conditions around giant planets, we need to go beyond Europa itself and address two more general questions at the scale of the Jupiter system: to what extent is its possible habitability related to the initial conditions and formation scenario of the Jovian satellites? To what extent is it due to the way the Jupiter system works? ESA’s Cosmic Vision programme offers an ideal and timely framework to address these three key questions. Building on the in-depth reconnaissance of the Jupiter System by Galileo (and the Voyager, Ulysses, Cassini and New Horizons fly-by’s) and on the anticipated accomplishments of NASA’s JUNO mission, it is now time to design and fly a new mission which will focus on these three major questions. LAPLACE, as we propose to call it, will deploy in the Jovian system a triad of orbiting platforms to perform coordinated observations of its main components: Europa, our priority target, the Jovian satellites, Jupiter’s magnetosphere and its atmosphere and interior. LAPLACE will consolidate Europe’s role and visibility in the exploration of the Solar System and will foster the development of technologies for the exploration of deep space in Europe. Its multi-platform and multi-target architecture, combined with its broadly multidisciplinary scientific dimension, will provide an outstanding opportunity to build a broad international collaboration with all interested nations and space agencies. Team members: full list available at . Full list of LAPLACE proposal members at .     

Stable satellites around extrasolar giant planets

In this work, we study the stability of hypothetical satellites of extrasolar planets. Through numerical simulations of the restricted elliptic three-body problem we found the borders of the stable regions around the secondary body. From the empirical results, we derived analytical expressions of the critical semimajor axis beyond which the satellites would not remain stable. The expressions are given as a function of the eccentricities of the planet, e _P, and of the satellite, e _sat. In the case of prograde satellites, the critical semimajor axis, in the units of Hill's radius, is given by a _E≈ 0.4895   (1.0000 − 1.0305 e _P− 0.2738 e _sat). In the case of retrograde satellites, it is given by a _E≈ 0.9309  (1.0000 − 1.0764 e _P− 0.9812 e _sat). We also computed the satellite stability region ( a _E) for a set of extrasolar planets. The results indicate that extrasolar planets in the habitable zone could harbour the Earth-like satellites.     

Numerical theories of motion of Triton and Nereid

The ephemerides of satellites of major planets are needed in planning spacecraft missions both for studying the satellites themselves and for navigational support during the flights of spacecraft in the vicinity of planets. In addition, accurate numerical theories of motion of the natural satellites of major planets make it possible to increase the accuracy of the ephemerides of their central planets based on positional (photographic and CCD) observations of the satellites. Numerical theories of Neptune’s satellites, Triton and Nereid, constructed within the framework of the ERA software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences are presented.     

Compositional anomaly of Ganymede and Callisto among the ice satellites as inferred from impact crater morphology

Differences in crater morphology between the Jovian and Saturnian-Uranian ice satellites implies a weaker surface strength for Ganymede and Callisto and thus a more concentrated composition of water. This compositional anomaly among the ice satellites is apparently due to a more complete migration of heavy material toward the inner part of the pre-planetary disc of the Jovian system than occurred in the discs of the Saturnian and Uranian systems.     

Cryovolcanism on the icy satellites

Evidence of past cryovolcanism is widespread and extremely varied on the icy satellites. Some cryovolcanic landscapes, notably on Triton, are similar to many silicate volcanic terrains, including what appear to be volcanic rifts, calderas and solidified lava lakes, flow fields, breached cinder cones or stratovolcanoes, viscous lava domes, and sinuous rilles. Most other satellites have terrains that are different in the important respect that no obvious volcanoes are present. The preserved record of cryovolcanism generally is believed to have formed by eruptions of aqueous solutions and slurries. Even Triton's volcanic crust, which is covered by nitrogen-rich frost, is probably dominated by water ice. Nonpolar and weakly polar molecular liquids (mainly N₂, CH₄, CO, CO₂, and Ar), may originate by decomposition of gas-clathrate hydrates and may have been erupted on some icy satellites, but without water these substances do not form rigid solids that are stable against sublimation or melting over geologic time. Triton's plumes, active at the time of Voyager 2's flyby, may consist of multicomponent nonpolar gas mixtures. The plumes may be volcanogenic fumaroles or geyserlike emissions powered by deep internal heating, and, thus, the plumes may be indicating an interior that is still cryomagmatically active; or Triton's plumes may be powered by solar heating of translucent ices very near the surface. The Uranian and Neptunian satellites Miranda, Ariel, and Triton have flow deposits that are hundreds to thousands of meters thick (implying highly viscous lavas); by contrast, the Jovian and Saturnian satellites generally have plains-forming deposits composed of relatively thin flows whose thicknesses have not been resolved in Voyager images (thus implying relatively low-viscosity lavas). One possible explanation for this inferred rheological distinction involves a difference in volatile composition of the Uranian and Neptunian satellites on one hand and of the Jovian and Saturnian satellites on the other hand. Perhaps the Jovian and Saturnian satellites tend to have relatively "clean" compositions with water ice as the main volatile (ammonia and water-soluble salts may also be present). The Uranian and Neptunian satellites may possess large amounts of a chemically unequilibrated comet-like volatile assemblage, including methanol, formaldehyde, and a host of other highly water- and ammonia-water-soluble constituents and gas clathrate hydrates. These two volatile mixtures would produce melts that differ enormously in viscosity The geomorphologic similarity in the products of volcanism on Earth and Triton may arise partly from a rheological similarity of the ammonia-water-methanol series of liquids and the silicate series ranging from basalt to dacite. An abundance of gas clathrate hydrates hypothesized to be contained by the satellites of Uranus and Neptune could contribute to evidence of explosive volcanism on those objects.     

Modelling the Jovian planets by a simple analytical algorithm

This paper models the structures of the Jovian atmospheres and cores by a simple analytical algorithm, which does not require the use of a computer. The method known as the MDV (Motz-Doorish Variable) method was first reported in the Irish Astronomical Journal (1989). It is a method to solve the Stellar Interior Equations (SIE) which dictate the structure of a star and/or the Jovian planets (Bodenheimer, 1986). The results are compared mainly, to the work of Stevenson (1982b) and found to be very agreeable. We include tabulated results of both the atmospheres and cores of Jupiter, Saturn, Uranus, and Neptune.     

Dust blobs in the solar nebula — primary distended atmosphere

When planetary accretion proceeds in the gas disk-solar nebula, a protoplanet attracts surrounding gas to form a distended H₂-He atmosphere. The blanketing effect of the atmosphere, hampering the escape of accretional energy, enhances the surface temperature of planets. Furthermore, evaporation of ice or reduction of surface silicate and metallic oxide can supply a huge amount of water vapor into the atmosphere, which would raise the temperature and promote evaporation. Evaporated materials can be efficiently conveyed outward by vigorous convection, and condensed dust particles should keep the atmosphere opaque during accretion. The size of this opaque atmosphere dust blob is defined by the gravitational radius, which exceeds 3 × 10⁸ m when the planetary mass is the Earth's mass (5.97 × 10²⁴ kg). This is larger than the radii of present Jovian planets and so-called brown dwarfs. The expected lifetime of dust blobs is 10⁶–10⁷ yr, which is longer than that of the later gas accreting and cooling stages of Jovian planets. The number of dust blobs could exceed that of Jovian planets. If the gas disk is rather transparent, the possibility of observing such objects with a distended atmosphere may be higher than that of detecting Jovian planets. Contamination of the gas disk by the dust from primary atmospheres is negligible.Paper presented at the Conference on Planetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.