Satellites of Planets in the Solar System

The satellites of the giant planets are of particular interest for the search of water and therefore also for astrobiology in general. A review about the evolution of the icy satellites of the giant planets has been given by Schubert et al., 2010 [298], 

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These space-based observatories and a number of terrestrial observatories have produced a growing body of data about five of the planets in the solar system—Mercury, Venus, Mars, Jupiter, and Saturn—as well as numerous other bodies, including comets, asteroids, and many planetary satellites, including our own Moon. 

The last planet-like object to be explored is Pluto. Since its discovery in 1930 by American astronomer Clyde Tombaugh (1906-97), Pluto has been considered one of the nine planets in the solar system. In August 2006, however, the International Astronomical Union established a new set of criteria for planets that Pluto did not meet. It is now considered a dwarf planet. In spite of its new designation, astronomers remain very interested in the chemical composition and physical characteristics of Pluto. Astronomers do have a fair amount of information about Pluto from ground-based observatories, the Hubble Space Telescope (HST), and the Infrared Astronomical Satellite. NASA s New Horizons space mission is expected to provide a great deal more detail about the strange and mysterious astronomical body. New Horizons was launched on January 19, 2006. It is expected to fly by Pluto and its satellite, Charon, in July 2015. 

Saturn is the second-largest planet in the solar system, after Jupiter. Its equatorial radius is 37,448 miles (60,268 km), about nine times that of Earth, and its mass is 568.46 x 1024 kg, about 95 times that of Earth. As of early 2007, scientists had found 56 satellites of Saturn, the largest of which is Titan, with a radius of 8,448 feet (2,575 km, about 50 percent larger than that of Earth s Moon), and a mass of 1,345.5 x IO20 kg (about twice that of the Moon). Saturn s density is 0.687 g/cm3, less than that of water. This fact means that (if one could find a body of water large enough) Saturn would float on water. It is the only planet with a density less than that of water. 

Saturn -- the second largest planet in the solar system. Saturn has beautiful rings of ice and rock and dust particles circling it. Saturn s atmosphere is composed of hydrogen, helium, methane, and ammonia. Saturn has 20 plus satellites. Saturn was named after the Roman god of agriculture. 

Pluto -- considered the smallest planet in the solar system. Pluto s atmosphere probably contains methane, ammonia, and frozen water. Pluto has 1 satellite. Pluto revolves around the sun every 250 years. Pluto was named after the Roman god of the underworld. 

Following another path of bifurcation in the hierarchy of complexity, one may now proceed from matter particles to the Earth and the Solar System, the Milky Way (that contains about as many stars - a hundred billion - as there are cells in a human brain), and the whole Universe. This latter involves regular stars (some with planets, satellites, asteroids and comets), neutron stars and dust clouds, which make up galaxies and clusters, and such strange objects as quasars, pulsars or black holes. The regularity of the distribution of planets in our solar system has inspired to Greek philosophers a correspondence with the musical scale that Kepler (who set up the laws of planetary motion) called the "harmony of the spheres". By transposing the orbital velocities of... 

Book II investigates the dynamical conditions of fluid motion. Book III displays the law of gi avitatioii at work in the solar system. It is demonstrated from the revolutions of the six known planets, including Earth, and their satellites, though Newton could never quite perfect the difficult theory of the Moon s motion. It is also demonstrated from the motions of comets. The gravitational forces of the heavenly bodies are used to calculate their relative masses. The tidal ebb and flow and the precession of the equinoxes is explained m terms of the forces exerted by the Sun and Moon. These demonstrations are carried out with precise calculations. 

A collision with a Mars-sized object may have resulted in the formation of the Earth s moon. Our moon is by no means the largest satellite in the solar system, but it is unusual in that it and the moon of Pluto are the largest moons relative the mass of the planets they orbit. Geochemical studies of returned lunar samples have shown that close similarities exist between the bulk composition of the moon and the Earth s mantle. In particular, the abimdances of sidero-... 

Star formation and the formation of star systems with planets around them, constantly takes place in dense interstellar clouds. The material present in these clouds is incorporated into the objects that are formed during this process. Pristine or slightly altered organic matter from the cloud from which our solar-system was formed is therefore present in the most primitive objects in the solar system comets, asteroids, and outer solar-system satellites. Pieces of asteroids (and perhaps comets) can be investigated with regards to these components through the analyses of meteorites (and eventually in samples returned from these bodies by spacecraft) in laboratories on Earth. The infall of asteroid and comet material from space may have contributed to the inventory of organic compounds on primordial Earth. 

Pluto, with a diameter of 2300 km, has now been demoted from the smallest planet to one of the largest Kuiper belt objects. Pluto and its satellite Charon could be considered a binary system because they are closer in size than any other known celestial pair in the solar system and the barycenter of their orbits does not lie within either body. There are also two smaller moons, Nix and Hydra. All four bodies are likely KBOs with similar compositions. Pluto has a thin atmosphere containing N2, with minor CH4, CO, and Ar. Curiously, the face of Pluto oriented towards Charon contains more methane ice, and the opposite face contains more nitrogen and carbon monoxide ice. 

Among places where condensates accreted into significant solid bodies, such as planets, habitable realms have always been rarer than places that were either too cold or too hot for life to exist. Much of our Solar System s mass is still far too hot for life. Most of the deep interiors of the gas giants and rocky planets are too hot, as is, of course, the Sun itself. Most of the surface area of solid bodies in the Solar System are too cold - the icy satellites of the outer planets and the myriad comets and Kuiper Belt Objects on the far outer fringes of the Solar System. In this sense, places like the surfaces of Earth and Mars and Europa s subsurface ocean are indeed very rare places. 

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. 

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