Satellites of Uranus and Neptune

On 24 October 2007, UVIS observed f Orionis (Alnitak) occulted by the plume (Hansen et al. 2006, 2008 [153, 154]). Water vapor transport may occur by (i) diffusion through pores in an icy matrix, (ii) hydrodynamic flow in open cracks. Approaching the surface, the molecules either escape as vapor or they condense close to the ice and transfer their latent heat to the ice. 

Waite et al., 2009 [350] found that ammonia is present in the plume, along with various organic compounds, deuterium and, very probably, Ar. The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180 K have been measured near the fractures from which the jets emanate. Ammonia (together with methanol and salts) acts as an antifreeze that permits the existence of liquid water down to temperatures as low as 176 K. Schneider et al., 2010 [295] searched for sodium in Enceladus water plumes. The lack of observable sodium in the vapor is consistent with a deep ocean, a freshwater reservoir, or ice. The plume particles are the most important source for particles in Saturn s E-ring. The observations are consistent with a subsurface ocean in contact with its rock core. There is no atomic sodium in the vapor however it is present in salts in Saturn s E ring (see also Spencer, 2(X)9 [314]). 

Spencer et al., 2009 [317] discussed Enceladus as an active cryovolcanic satellite. Plumes, both large and small, spray water ice out from many locations along the famed tiger stripes near Enceladus south pole. 

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Cruikshank D. and Brown R. H. (1986) Satellites of Uranus and Neptune, and the Pluto-Charon System. In Satellites (eds. J. A. Burns and M. S. Matthews). University of Arizona... 

Diacetylene (HC=C—C=CH) has been identified as a component of the hydrocarbon rich atmospheres of Uranus Neptune and Pluto It is also present m the atmospheres of Titan and Triton satellites of Saturn and Neptune respectively... 

How do giant planets form Two different models, disk instability versus core accretion followed by gas collapse, are viable. They require very different timescales, have very different implications for satellite formation and internal composition, and may have implications for the ubiquity of giant planets and terrestrial planets around other stars. The formation of Uranus and Neptune is even less well understood, and no agreement exists as to whether these are stillborn Jupiters or the product of a distinct kind of formation process. 

The detection of atmospheres on extrasolar planet is a very difficult task. 71% of the Earth is covered by oceans but up to now it is the only planet with water in liquid form on its surface. Venus might have had water on its early history, on Mars water may exist in a frozen state near the surface and climatic changes have occurred and formed river-like structures that are observed on its surface. There exists the possibility to find condensed water in the atmospheres of Jupiter and Saturn and in deeper layers of Uranus and Neptune. Subsurface oceans may exist on several satellites of the giant planets. But how can we detect water on extrasolar planets, how can we detect whether these objects have even an atmosphere ... 

Our solar system consists of the Sun, the planets and their moon satellites, asteroids (small planets), comets, and meteorites. The planets are generally divided into two categories Earth-like (terrestrial) planets—Mercury, Venus, Earth, and Mars and Giant planets—Jupiter, Saturn, Uranus, and Neptune. Little is known about Pluto, the most remote planet from Earth. 

Effects of condensation are also seen in the bulk compositions of the planets and their satellites. The outer planets, Uranus and Neptune, have overall densities consistent with their formation from icy and stony solids. The satellites of Uranus have typical densities of 1.3g/cm which would tend to indicate a large ice com-... 

Neptune is the eighth planet from the Sun and about four times the size of Earth. Astronomers consider Neptune to form with Uranus a subgroup of the Jovian planets (Jupiter, Saturn, Uranus, and Neptune). Neptune and Uranus are similar in size, mass, periods of their rotation, the overall features of their magnetic fields, and ring systems. However they differ in the structure of their atmospheres (perhaps the more conspicuous features of Neptune s clouds are caused by its significant internal energy source, which Uranus lacks), the orientations of their rotation axes, and in their satellite systems. 

At the time, more than a dozen planetary satellites had already been discovered for Jupiter, Saturn, Uranus, and Neptune. None had been found for Venus or Mercury, nor were they likely to be found, given the proximity of these planets to the Sun. Mars likewise had no satellites. .. or, at least, none that had yet been discovered. 

The outer or giant planets - Jupiter. Saturn, Uranus, and Neptune - are massive low-density bodies with a rocky core surrounded by deep layers consisting mainly of solid, liquid, and gaseous hydrogen and helium. They are much further from the sun and therefore much cooler. All have large numbers of satellites Jupiter has at least 63 Saturn at least 61 Uranus 27 and Neptune 13. The outer planets also have ring systems composed of smaller bodies, rocks, dust, and ice particles. 

Uranus and Neptune, are large, massive bodies, distant from the Sun, with atmospheres composed mostly of hydrogen and helium. The remaining planets Mercury and Pluto are small bodies. Mercury orbits close to the sun and has a tenuous atmosphere In which atomic sodium and potassium have been seen. Pluto lies at a great distance from the Sun and Its surface Is frozen. It may have an atmosphere containing methane, similar perhaps to those of the satellites Titan of Saturn and Triton of Neptune, which have atmospheres of nitrogen with an admixture of methane. 

Precise measurements of the orbital periods of Charon (6.387 223 0.000017 day) and the difficult measurement of the orbital wobble of both bodies with respect to their common center of mass lead to estimates of the masses of both (Tholen Buie, 1997). Together with a measurement of the radii an estimate of the mean densities can be derived. The density of Pluto was found to be between 1.92 and 2.06 and that of Charon between 1.51 and 1.81 gcm , indicating a substantial fraction of rocks in addition to ices for Pluto and a smaller amount of hydrated rocks below water ice for Charon. Consequently, Pluto is much more similar in composition to Neptune s retrograde satellite Triton (density = 2.043 0.0121, radius = 1352.6 2.4 km see McKiimon et al., 1995), while Charon seems to be more similar to the smaller, icy satellites of Neptune and Uranus. For a discussion of Triton and the smaller satellites of Neptune see the book edited by Cmikshank (1995) and the paper by Quirico etal. (1999). The satellites of Uranus are discussed in the book edited by Bergstralh et al. (1991). 

The term "Solar System ice" denotes in general a solidified volatile and/or mixtures of solidified volatiles. The Solar System ices are mostly water ice H2O, but also solidified CO2, CO, NH3, N2, SO2, CH4 and many other simple molecules as well as the organics. On the surfaces of many of the satellites of the giant planets (Jupiter, Saturn, Uranus, and Neptune) water ice is the dominant component. Therefore, in the following we will adopt the common assumption that a satellite is composed of water ice, and silicates. The radii and the masses of all satellites but the smallest ones are well known. Therefore their densities are known as well, see Table 1. Taking into account that the densities of water ice are about 940,1190, and 1360 kg m at phases I, II, and VI, respectively, and that the density of the silicates is (3400 400) kg m" the mass ratio C of silicates to total mass of the satellite can be estimated. This is rather simple for large satellites however, the estimate can fail for smaller satellites because of the possible bulk primordial porosity left fi-om an epoch of formation. 

Neptune s large satellite Triton, which has a very thin nitrogen atmosphere with clouds, plumes, and haze, an extremely cold surface with nitrogen, methane, carbon monoxide, and carbon dioxide ices which interact with the atmosphere, and a fairly high mean density, make it seem more like Pluto than the other satellites of Neptune and those of Saturn and Uranus. Not enough is known about Pluto to explore these similarities this probably awaits future missions to Pluto, especially the New Horizons mission that NASA hopes to launch in 2006. 

The outer planets also tend to have a number of satellites with (at last count) 56 orbiting Saturn, 63 around Jupiter, 27 around Uranus, and 13 around Neptune, compared to the virtual absence of satellites in the inner planets Mercury with 0 Venus, 0 Earth, 1 and Mars 2. 

Kuiper s list of astronomical accomplishments is impressive. In addition to his work on binary stars, the atmospheres of planets and satellites, and the formation of the solar system, he discovered the fifth moon of Uranus, Miranda, and Neptune s second moon, Nereid he was an early advocate of the use of jet airplanes for high-altitude astronomical observations and he accurately predicted the nature of the lunar surface before any human had walked on it. In recognition of these achievements, Kuiper was awarded the Janssen medal of the French astronomical society and the Order of Orange Nassau by the Dutch government. Kuiper died in Mexico City on December 24,1973, while examining a number of possible sites for a new observatory. 

Because of the faintness of its radio emission, Pluto was the last planet to be detected. A few asteroids, satellites, and comets have been measured as well. Nonthermal radio emission has been measured from Jupiter, Saturn, Uranus, Neptune, and Earth. In this article we give an overview of the techniques used by planetary radio astronomers and discuss what has been learned from the measurements and what can be done in the future. In the interest of brevity, we do not discuss specific observations of asteroids and satellites, although they rightfully belong in any discussion of planetary radio astronomy. 

The voyager mission consisted of two satellites launched in 1977 that reached Jupiter in 1979, Saturn in 1981 and Voyager 2 reached Uranus in 1986 and Neptune in 1989. 

Like the case for Uranus s rings, the origin and evolution of Neptune s rings are unknown. Are they the result of earlier tidal disruption of other nearby satellites Are they a transitory phenomenon, or will they persist for millions or billions of years Comparison of the positions of the arcs in the Adams ring observed by Voyager 2 in 1989 with their positions extrapolated back in time to 1984 and 1985 shows that they match the positions of three occultations of stars observed in those years. This indicates that the arcs in the Adams ring are stable over time intervals of at least five years. 

Researchers have learned a vast amount of new information about Jupiter, Saturn, Uranus, Neptune, Pluto and the Kuiper Belt Objects in the last century. Improved terrestrial telescopes, the Hubble Space Telescope, and space explorations such as Voyager 1 and 2, Galileo, and Cassini have produced new data that will take astrochemists years to analyze and interpret, providing them with even more detailed information about the chemical composition of the atmospheres, satellites, surfaces, and other features of the outer planets and their associated bodies. 

These steps are represented by the index n in Table 5.4. Each value of n represents an allowed orbital distance for a satellite from its parent attractor. The planets have indices of Neptune(O), Uranus(2), Saturn(6), Jupiter(9), Asteroids(12), Mars(15), Earth(18), Venus(21) and Mercury(24). Because of the self-similar symmetry of the golden spiral this progression can be continued indefinitely on a continuously increasing scale. 

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