Friday, March 19, 1999 Published at 14:16 GMT
Mysterious moon's methane sea
Does an ocean lie beneath this ice crust?
By BBC News Online Science Editor Dr David Whitehouse
Seen in close-up only once, Neptune's mysterious moon Triton is one of the Solar System's strangest bodies.
Images were sent back to Earth for a few hours during the Voyager spacecraft's brief encounter with the Neptune system in 1989.
Triton is a frozen world, with unexplained features on its surface and strange "ice geysers."
It may also have an ocean just beneath the ice - an ocean made of liquid methane or ammonia. It would be like nothing ever found before.
A new analysis of the old Voyager data has just been completed.
The findings from the study were revealed at the Lunar and Planetary Science Conference being held in Houston, Texas, this week.
The research shows that Triton's surface may be about half a billion years old - and possibly even younger than that. This suggests that resurfacing is actively taking place.
Scientists believe liquid is coming from below and freezing on the surface of Triton, obliterating all but the youngest craters.
For years, researchers have speculated about a subsurface ocean on Europa, a moon of Jupiter. There might also be such an ocean on another Jovian satellite, Gannymede.
The hope is that such oceans could contain water that would sustain some sort of extreme lifeform.
But if the scientists are right and Triton has an ocean of ammonia or liquid methane, such life would be rather unlikely.