Neptune satellites

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... 

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-... 

Solid CH4 on Triton and Terrestrial Methane Hydrate. - 5.4.1 Radicals in Solid CH4 and on Triton. Methane (CH4) and nitrogen are gaseous molecules on Earth but are frozen and solids under the lowest temperature of 37K at Triton, a satellite of Neptune. Craters of solidified CH4 and N2 and black smoke consisting of gaseous N2 and solid CH4 were discovered by the Voyager II a few km above the ground volcanic eruptions in 1989. 

This division corresponds to the division into rocky planets of the inner solar system and gaseous planets of the outer solar system, separated by the minor planets. By analogy, a larger sequence of solar satellites (planetoids, comets), of which the Pluto/Charon system is the first, is predicted to continue the regular progression beyond Neptune. 

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. 

Neptune s largest moon, Triton, was discovered within weeks of the discovery of the planet itself. It is one of the most distant objects in the solar system. Even the outermost planet, Pluto, and its moon, Charon, spend considerable time on their eccentric orbits closer to the Sun than Triton. Its nature remained a mystery until the advent of new astronomical methods in the 1970s and 1980s and the flyby of the Voyager 2 spacecraft in 1989. In many ways, it is a planetary body on the edge —on the outer edge of the main part of the solar system, and the inner edge of the realm of comets and the recently discovered Kuiper belt objects. As such, it shares some of the characteristics of the icy satellites of the rest of the outer solar system with some of the nature of the colder, more distant, cometary bodies. 

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... 

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. 

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. 

G.P. Kuiper discovered a second satellite, Nereid, in 1949. It is a small, feint (nineteenth magnitude) object in an orbit around Neptune that is distant (3,423,821 mi [385,513,400 km] mean distance) from it, very elliptical (eccentricily 0.756), and h ly inclined (29° to Neptune s equator). A third satellite was suspected at about a 45,954 mi (74,000 km) distance from Neptrme s center because of a simultaneous 8.1 second decrease in the br hlness of a star observed simultaneously from two locations 4 mi (6 km) apart in May 1981. 

From 1982, Neptune was suspected to have rings like the other Jovian planets. However, confirmation of suspected occultations of stars by rir s of Neptune was not definite occultaticns by possible rings were only observed sometimes. This led to the theory that Neptune had a set of incomplete arc rights which were maintained by gravitational perturbations from one or more shepherd satellites which were still undiscovered. 

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. 

All of Neptune s six innermost satellites are very dark, having albedos of 0.065 or less. Proteus, the largest and outermost of the newly discovered satellites, had details on its surface imaged. It is heavily cratered, with a 93 mi (150 km) diameter crater visible there. Proteus turns out to be somewhat larger than Nereid and has a mean radius of 250 mi (400 km) images of Proteus indicate it to be decidedly non-spherical. The images indi-... 

The history of Neptune and its system of rings and satellites was likely profoundly affected by the capture of of Triton. It is thought that Neptune had an earlier system of satellites and perhaps rings, but the capture of Triton disrupted Neptune s original system causing possible ejection of some satellites, reformation of others (i.e., the... 

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 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. 

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. 

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