7 Mar 2009, 1325 hrs IST, ANI

WASHINGTON: A new study has found that Pluto has an upside-down atmosphere compared with Earth, with temperatures rising, rather than dropping, with altitude on the dwarf planet.

According to a report in National Geographic News, this was found by astronomers using the European Southern Observatory's Very Large Telescope, which helped to make the most detailed measurements to date of the concentration of the greenhouse gas methane in Pluto's atmosphere.

The measurements showed that methane is the second most abundant gas in Pluto's atmosphere, and that the gas is actually warmer at higher elevations than at the icy surface.

As a result, Pluto's upper atmosphere is about 90 degrees Fahrenheit (50 degrees Celsius) warmer than the planet's surface.

The team, led by Emmanuel Lellouch of France's Paris Observatory, speculates that there is a thin frozen layer, or frozen patches, of methane and other gases on Pluto's surface.

As Pluto orbits closer to the sun, the frozen gases vaporize. This process, called sublimation, cools Pluto's surface while warming the planet's atmosphere.

According to Leslie Young, deputy project scientist for NASA's New Horizons probe, the new discovery is exciting, especially since it hints at future unexpected observations from New Horizons, which is scheduled to settle into orbit around Pluto in 2015.
"We know that Pluto changes with time as it moves around the sun," Young said.

So combining Earth-based observations with New Horizons data taken from Pluto's orbit will provide new clues about the dwarf planet's behaviour.