Today we have a guest post by Laura Arnold about Neptune's moon Triton!
The largest moon of Neptune, and the 7th largest moon in the solar system, has a peculiar orbit. It orbits opposite the rotation of Neptune. Moons are theorized to form in the same way solar systems are, from a rotating flattened disk of gas and dust. And the fact that all of the planets orbit the Sun in the same direction as the sun rotates supports this theory. Scientists think that Triton's backward orbit indicates that it once orbited the Sun and was captured by Neptune when they came close to each other. In order for a massive body to enter into orbit around Neptune and not just whizz right by it would have to lose a lot orbital energy, or angular momentum. One theory states, that if Triton had a moon itself or was in a planetary binary system, Triton could be captured if the excess orbital energy had been carried off by its satellite which with all this energy would be ejected from orbit around Triton and Neptune
Voyager 2 returned pictures of Triton in 1989, revealing an icy surface with very few impact craters. The surface of Triton smooth in some places and crinkled, like the skin of a cantaloupe, in other places. Because of the lack of cratering, it is thought that Triton's got a face-lift around 10-100 million years ago. This resurfacing could be done if ice in Triton's interior was heated due to tidal interactions with Neptune or heat from radioactive decay. This would provide for a liquid ocean under the icy surface of Triton, similar to Jupiter's moon Europa and Saturn's moon Enceladus. If pressure built up enough, ice volcanoes (cryovolcanism) could form spewing liquid, likely water mixed with ammonia and methane, onto Triton's dreadfully cold surface (colder than -382 F) which would then freeze. Voyager 2 saw two active geysers on Triton which spewed nitrogen gas as high as 8 km into the air. The energy powering these geysers is thought to come from sunlight, as these arose around the point on Triton which receives the most sunlight (though this is still about 1 thousandth of what Earth receives.)
Image credit: NASA/JPL/USGS
