Atmospheric dynamics on the outer planets and some of their satellites

A short review of the atmospheric dynamics for the outer planets and some of their satellites with atmospheres is presented. Their physical properties are discussed. A survey of observational data for atmospheric motions on the large planets is presented and similarity parameters are given for all objects. General problems of the vertical structure of atmospheres are then considered with some detailed discussion for rarefied atmospheres on Io and Ganymede. The low densities of these atmospheres make their dynamics similar to those of the thermospheres of the terrestrial planets but with a specific boundary layer. The atmospheric temperature regime must be strongly coupled to that of their surface, and so winds should be of the order of the velocity of sound. Similarities and differences are noted between the dynamics of Titan and possibly of Pluto and the circulation on Venus. For large and rapidly rotating planets, some analogies with the oceans are pointed out. The “soliton” hypothesis is discussed in some detail for circulation perturbations observed on Jupiter's disk. Finally, it is noted that the bimodal rotation period found for Neptune [D.P. Cruikshank, Astrophys. J. 220, 157–159 (1978)] may be interpreted as an indication of an equatorial jet on the planet with a relative velocity of about 140 m sec^?1.     

Abundance of organic compounds photochemically produced in the atmospheres of the outer planets

Organic photochemical syntheses in the Jovian atmosphere were simulated by irradiating, at 147 nm, gaseous mixtures of methane and ammonia with varying quantities of hydrogen. An excess of H₂ did not eliminate organic synthesis but did affect the yields quantitatively and qualitatively.     

The international outer planets watch atmospheres node database of giant-planet images

The Atmospheres Node of the International Outer Planets Watch (IOPW, formerly known as International Jupiter Watch; Russell et al., 1990) intends to encourage and coordinate the imaging observations and study of the atmospheres of the Giant Planets. The main activity of the atmospheres node is to provide an interaction between the professional and amateur astronomical communities maintaining a large database of images of the giant planets (primarily Jupiter and Saturn but with increasing contributions of Uranus and Neptune too). The observational datasets of Jupiter and Saturn correspond to images obtained in the visible range (300 nm-1 μm), during the last decade, most of them performed by amateur observers. We here describe the organization and structure of the database as posted on the Internet and in particular the PVOL software (Planetary Virtual Observatory Laboratory) designed to manage the site in the spirit of the Virtual Observatory projects. We also describe with examples the important role of the amateur-professional collaboration in the study of the atmospheres of Jupiter and Saturn in an epoch of large telescopes and spacecraft observations of both planets.     

Aqueous alteration affecting the irregular outer planets satellites: Evidence from spectral reflectance

The surface reflectance properties of the irregular outer planets satellites are probed for evidence for the presence of aqueous alteration products on their surfaces using the strong correlation between the 3.0-μm water of hydration absorption feature and the 0.7-μm Fe²⁺ → Fe³⁺ oxidized iron feature seen in low-albedo asteroid reflectances, in an effort to expand our understanding of the composition of the precursor bodies from which the dynamical satellite clusters are derived. Equations converting Johnson V and Kron-Cousins RI photometry to Eight Color Asteroid Survey v (0.550 μm), w (0.701 μm), and x (0.853 μm) photometry are derived from relationships defined by Howell (1995, Ph.D. thesis), and coupled with an algorithm previously defined to detect the presence of the 0.7-μm absorption feature in ECAS asteroid photometry [Vilas, F., 1994. Icarus 111, 456-467]. Broadband VRI photometry of Ch-class Asteroid 19 Fortuna acquired during 2004 confirms the efficacy of this method of identifying the presence of the 0.7-μm feature. Photometric observations of many recently discovered irregular outer jovian, saturnian, uranian, and neptunian satellites, coupled with limited asteroid spectroscopy, were examined for the presence of aqueous alteration. The dynamical clusters of outer irregular jovian satellites are mixed between objects that do and do not show this absorption feature. Multiple observations of some objects test both positively and negatively, similar to the surface variegation that has been observed among many C-class asteroids in the main asteroid belt. Evidence for aqueous alteration on these jovian satellites augers for an origin in or near the same location as the asteroids now occupying the aqueous alteration zone (2.6-3.5 AU), at heliocentric distances internal to Jupiter's orbit. Among the saturnian irregular satellites, only S IX Phoebe shows limited evidence of aqueous alteration from ground-based observations. The other satellites show no sign of this feature, and have general reflectance properties very similar to the D-class asteroids, supporting an origin for their precursor bodies in the outer Solar System, perhaps the Centaur region. Only two uranian satellites were tested: U XVII Caliban tests positively for the feature. The differences in surface reflectance properties support the idea that Caliban and U XVI Sycorax derive from separate parent bodies. One observation of neptunian satellite N II Nereid shows no sign of this absorption feature.     

Extrasolar low-orbit planets: Dissipation of their atmospheres and probable magnetic field

Analysis of the data obtained during transits of low-orbit extrasolar planets across the stellar disk yields different estimates of their atmospheric loss rates. Experimental data point to the probable existence of several distinct subtypes of extrasolar giant planets, including “hot Jupiters” of low density (HD 209458b), with massive cores composed of heavy elements (HD 149026b), and others. We show that the expected hot-Jupiter mass losses due to atmospheric escape on a cosmogonic time scale do not exceed a few percent, while the losses through Jeans dissipation are negligible. We also argue that low-orbit giant planets should have a strong magnetic field that interacts with circumstellar plasma with the planet’s supersonic orbital velocity. The magnetic field properties can be used to search for extrasolar planets.     

The oblateness effect on the solar radiation incident at the top of the atmospheres of the outer planets

Calculations of the daily solar radiation incident at the top of the atmospheres of Jupiter, Saturn, Uranus, and Neptune, with and without the effect of the oblateness, are presented in a series of figures illustrating the seasonal and latitudinal variation of the ratio of both insolations. It is shown that for parts of the summer, the daily insolation of an oblate planet is increased, the zone of enhanced solar radiation being strongly dependent upon the obliquity, whereas the rate of increase is fixed by both the flattening and the obliquity. In winter, the oblateness effect results in a more extensive polar region, the daily solar radiation of an oblate planet always being reduced when compared to a spherical planet. In addition, we also numerically studied the mean daily solar radiation. As previously stated by A.W. Brinkman and J. McGregor (1979, Icarus, 38, 479–482), it is found that in summer the horizon plane is tilted toward the Sun for latitudes less than the subsolar point, but is titled away from the Sun beyond this latitude. It follows that the mean summer daily insolation is increased between the equator and the subsolar point, but decreased poleward of the above-mentioned limit. In winter, however, the horizon plane is always tilted away from the Sun, causing the mean winter daily insolation to be reduced. The partial gain of the mean summertime insolation being much smaller than the loss during winter season evidently yields a mean annual daily insolation which is decreased at all latitudes.     

Origin of the atmospheres of the terrestrial planets

The monotonic decrease in the atmospheric abundance of ³⁶Ar per gram of planet in the sequence, Venus, Earth, and Mars has been assumed to reflect some conditions in the primitive solar nebula at the time of formation of the planetary atmospheres, having to do either with the composition of the nebula itself or the composition of the trapped gases in small solid bodies in the nebula. Behind such hypotheses lies the assumption that planetary atmospheres steadily gain components. However, not only can gases enter atmospheres; they may also be lost from atmospheres both by adsorption into the planetary interior and by loss into space as a result of collisions with minor and major planetesimals. In this paper a necessarily qualitative discussion is given of the problem of collisions with minor planetesimals, a process called atmospheric cratering or atmospheric erosion, and a discussion is given of atmospheric loss accompanying collision of a planet with a major planetesimal, such as may have produced the Earth's Moon.     

On the stability of the inner planets,satellites and close binaries

I consider the range of Hill stability in the restricted circular problem of three bodies when the larger one of the two principal bodies has a finite oblateness. I show that the range r satisfies the equation

$\text{r =}\text{1? μ}\text{C}{}_{\mathrm{cr}}\text{? 3μ + μr}{}^2\text{? v (1? μ)r}{}^{\mathrm{?3}}\text{±(2 + 3v)}\text{(1 ? μ}\text{1 +}\text{3v}\text{r}{}^2\text{r}\text{,}$

where μ is the mass parameter and v is an oblateness parameter. This result is applied to the solar system, the Earth-Moon system and binary star systems. It is then shown that, all the inner planets of the solar system, the great majority of asteroids and some short-period comets are Hill stable, that direct artificial satellites of the Earth are more stable than retrograde ones, and that contact binaries possess cores between which no mass exchange takes place.     

Geology of terrestrial planets with dynamic atmospheres

Geological exploration of the solar system shows that solid-surfaced planets and satellites are subject to endogenic processes (volcanism and tectonism) and exogenic processes (impact cratering and gradation). The present appearance of planetary suffaces is the result of the complex interplay of these processes and is the linked to the evolution of planets and their environments. Terrestrial planets that have dynamic atmospheres are Earth, Mars, and Venus. Atmospheric interaction with the surfaces of these planets, oraeolian activity, is a form of gradation. The manifestation of aeolian activity is the weathering and erosion of rocks into sediments, transportation of the weathered debris (mostly sand and dust) by the wind, and deposition of windblown material. Wind-eroded features include small-scale ventifacts (wind-sculptured rocks) and large-scale landforms such as yardangs. Wind depositional features include dunes, drifts, and mantles of windblown sediments. These and other aeolian features are observed on Earth, Mars, and Venus.     

The formation of the outer planets

One of the outstanding problems in planetary cosmogony is to account for the depletion of hydrogen in the outer planets, Neptune and Uranus. It is suggested that these planets were originally similar to the major planets but that the settling towards the centre of grains, enriched by substances such as methane, ammonia and water because of the low temperatures, released enough energy to cause the evaporation of most of the hydrogen.     

Observations of Saturn's outer ring and new satellites during the 1980 edge-on presentation

Observations of Saturn's satellites and external rings during the 1980 edge-on presentation were obtained with a focal coronograph. A faint satellite traveling in the orbit of Dione and leading it by 72° has been detected, together with the two inner satellites already suspected (cf. J. W. Fountain and S. M. Larson, 1978,Icarus36, 92–106). The external ring has been observed on both east and west sides; it may extend up to $\text{?8.3}$ Saturn radii, and appears structured.     

The origin of the atmospheres of the earth and the planets

From a systematic analysis of the whole history of the protoplanetary cloud and the observational facts of the Earth's atmosphere, we propose a new theory of the origin of the atmospheres of the Earth and the planets. For the Earth-like planets, there were extended primordial atmospheres originating from the protoplanetary cloud by the accretion of the planetary embryoes. These primordial atmospheres existed on a time scale of 10³–10⁷ years and were composed of chemically reducing gases. The presence of such a reducing atmosphere may be of great significance to the theories of cosmogony and the origin of life.The contents are 1. The escape of the nebula and the planetary atmospheres. 2. The thermal dissipation of the atmospheres and their blowing-off by the solar wind. 3. The accretion of gases by the planetary enbryoes. 4. The primordial atmospheres.