Thursday, June 25, 1998 Published at 17:26 GMT 18:26 UK
Neptune's moon is getting warmer
Triton is getting warmer
Observations made by the Hubble Space Telescope and ground-based instruments reveal that Neptune's largest moon, Triton, has warmed significantly since the Voyager spacecraft visited it in 1989. Our science editor Dr David Whitehouse reports.
"Since 1989, at least, Triton has been undergoing a period of global warming - percentage-wise, it's a very large increase," said Dr James Elliot of the Massachusetts Institute of Technology.
The observations are published in the journal Nature.
The warming is causing part of Triton's frozen nitrogen surface to turn into gas, thus making its thin atmosphere denser.
The 5% increase means that Triton's temperature has risen from -236°C to -234°C.
It might not be much but if Earth experienced a similar change in global temperature over a comparable period it could lead to significant climatic changes.
Triton, however, is a simpler world than Earth, with a much thinner atmosphere, no oceans, and a surface of frozen nitrogen.
"With Triton, we can more easily study environmental changes because of its simple, thin atmosphere," Mr Elliot said. By studying these changes on Triton, the scientists hope to gain new insight into Earth's more complicated atmosphere.
Triton's warming may be caused by seasonal changes in its polar ice caps. It is currently approaching southern summer, a season that occurs every few hundred years.
During this time, the moon's southern hemisphere receives more direct sunlight, which heats its polar ice caps.