Triton, the largest moon of Neptune. Because Triton has a retrograde orbit (opposite that of it's planet), it was likely captured by Neptune's gravitational pull from the Kuiper Belt. It's about the same size and has a very similar makeup to Pluto, another Kuiper Belt object. Triton's orbit is slowly shrinking, and it is expected that in about 3.6 billion years, it will either collide with Neptune or be destroyed, forming a Saturn-like ring system.
Orbiting a mere 3,700 miles above the surface of Mars, Phobos is closer to its planet than any other moon in our solar system. Mars’ gravity is drawing in Phobos by about 6.6 feet every 100 years. Scientists expect Phobos to be pulled apart in 30-50 million years by tidal forces, the mutual gravitational pull of the planet and the moon. The same fate may await Neptune’s moon Triton, which is also slowly falling inward towards its planet. (NASA/JPL-Caltech/University of Arizona)
This color photo of Neptune's largest moon Triton was obtained by NASA's Voyager 2 probe on Aug. 24, 1989, from 330,000 miles away. The resolution is about 6.2 miles, sufficient to begin to show topographic detail. CREDIT: NASA/JPL
This is Neptune’s moon, Triton, taken in 1989 by Voyager 2 - the only spacecraft ever to pass it. Triton has fascinating terrain, a thin atmosphere & even evidence for ice volcanoes on this world of...
(August 25, 1989) Voyager 2 was the first spacecraft to observe the planet Neptune and its two satellites: Triton, the largest, and Nereid. The most obvious feature of the planet is its blue color, the result of methane in the atmosphere. (Credit: NASA)