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Pluto's icy twin?

Our solar system has several large moons, some of which probably deserve being called planets in their own right. Of course the status of these worlds, as natural satellites of larger worlds, relegates them to the third-class realm of moons. Case in point: Triton, the ringed planet Neptunes largest natural satellite among eight moons. Its a volcanically active moon and boasts the solar systems coldest surface temperature recorded so far minus 391 degrees F (minus 199 degrees C). It looks like Triton is more than a mere moon; it is likely a former planet, too once having its own independent orbit around our Sun. It was forced into its current orbit around Neptune by the gas giants powerful gravity. This event occurred millions of years ago. Triton, 1,680 miles (2,704 kilometers) in diameter, orbits 220,438 miles (369,245 kilometers) from Neptune. Every 82 years, Tritons orbit places it between Neptune and the Sun. During this time, a weird effect occurs reflected light from giant Neptunes blue-colored methane atmosphere turns Tritons icy surface an eerie pale blue. Normally, Tritons ice-covered surface is salmon-pink in color due to its surface mixture of water ice, methane, nitrogen and dust. Covered in frozen seas and continents, Triton sports violent ice volcanoes that blow skyward for miles. Pressure beneath the moons icy surface forces trapped volcanic gases below to blow from surface vents and fissures. Triton is most certainly a doomed moon. Strong tidal forces between the former planet and Neptune cause Triton to orbit in reverse. As its orbit decays, Triton is slowly moving closer to Neptune. In less than 100 million years, the big moon will approach within 2-3,000 miles of Neptune. Once reaching Roches Limit the point at which gravitational stresses cause a planet or moon to begin to break up and form rings; named after French astronomer Edward Roche Triton will be shattered by the titanic Neptunian tidal forces. While large fragments of the doomed moon will plunge into Neptunes atmosphere, other pieces will likely expand the gas giants extant multiple-ring system. But beyond these few facts, we know very little about this mysterious ex-planet. It is suggested that Triton might be a twin of the more distant ninth planet Pluto, but with only a few electronic images snapped by the flyby Voyager 2 spacecraft in August 1989 astronomers dont have much else to go on. Well have to wait until 2015 when NASAs fast flyby spacecraft called New Horizons takes the first photographs of Pluto. Then well see if Triton and Pluto are dwarf twins that were seperated at birth. Whats in the Sky: Look for the constellation Ophiuchus, the serpent bearer, in the southernwestern sky this week. One of its most impressive stars is Zeta Ophiuchi. Its hard to locate; none of the constellations stars are bright to the naked eye. Lou Varricchio, M.Sc., lives in Vermont. He is a former NASA science writer and holds undergraduate degrees in communications and a graduate degree in space studies. He is currently part of the NASA-JPL Solar System Ambassador program in Vermont.

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