Triton, Neptune’s largest moon, has the coldest surface in the solar system and is believed to be a captured Kuiper belt object. It has a retrograde orbit and may have sent Neptune’s missing satellites into eccentric orbits. Triton has a unique “melon ground” surface and polar ice caps. It reflects 60-95% of the light that reaches it and is one of the “big seven” satellites of the solar system. Voyager 2 took high-resolution images of Triton in 1989, and it will remain the most distant solar system body photographed at this resolution until the New Horizons spacecraft reaches Pluto in 2015.
Triton is the largest moon of the planet Neptune, with the distinction of having the coldest known surface in the solar system, at about 34.5 K. Triton is widely believed to be a captured Kuiper belt object. The Kuiper belt is a second asteroid belt beyond the orbit of Neptune. Pluto and Eris are examples of Kuiper belt objects.
On August 25, 1989, the Voyager 2 space probe made a flyby of the Neptunian system and took high-resolution images of Triton. It is one of the most distant solar system bodies to be photographed at this resolution and will remain so until the New Horizons spacecraft reaches Pluto in 2015. Triton will also be the only likely Kuiper belt object to be photographed at this resolution until 2015 .
Triton is quite large: at 2700 km (1678 mi) in diameter, it is about 78% the size of our Moon. It is considered one of the “big seven” satellites of the solar system, along with Ganymede and other large satellites. Unique among the large satellites, it has a retrograde orbit, meaning it orbits “the wrong way,” highly suggestive that it’s a captured Kuiper belt object. Neptune has relatively few satellites compared to other gas giants, and it is thought that Triton’s capture may have sent the missing satellites into eccentric orbits that either collided with Neptune or spiraled apart beyond Neptune’s gravity.
Triton has a distinctive “melon ground” surface composed of extremely cold, dirty ice. Triton is similar in size and composition to Pluto, with relatively light features and not too many noticeable impact craters. Triton may have formed far away from the Sun. Its surface has several ridges, created during alternating cycles of thawing and freezing. Triton likely experienced significant tidal heating in the past, as its eccentric orbit normalized.
Triton has polar ice caps. Its surface is so light that it reflects 60-95% of the light that reaches it, compared to our Moon which only reflects 10% of the light. If Triton were in our night sky instead of the Moon, the night would be over ten times brighter than it is now!
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