Here’s a parting shot from the Voyager 2 spacecraft of the planet Neptune and its large moon Triton taken shortly after the historic flyby of August 25, 1989.
Triton is an odd moon. Inclined 23 degrees from the plane of Neptunes equator and orbiting the planet in the opposite direction of the planet’s rotation would seem to indicate Triton was captured by Neptune’s gravity and not formed with the planet. Many moons in the solar system are retrograde (mostly around Jupiter) but Triton is by far the largest, at 2,706 km, it’s not much smaller than our moon.
Triton is very cold, only 38 Kelvin or – 235 C (-391 F). You’d think it would be frozen solid, yet the moon has a rather “young” surface. It is thought when the moon was captured it not unxepectedly had an eliptical orbit which became circular over time thanks to tidal forces from Neptune. The flexing and streching of the moon created heat in the interior of the moon and led to volcanic activity. Volcanic activity in this case would involve ices and not lava.