Orbiter makes Mars atmosphere discovery

BOULDER, Colo., April 21 (UPI) -- The Mars Reconnaissance Orbiter has found the amount of atmosphere on Mars changes dramatically as the tilt of the planet's axis varies, U.S. researchers say.

The NASA planetary probe's ground-penetrating radar identified a large, buried deposit of frozen carbon dioxide, or dry ice, at the Red Planet's south pole, and scientists suspect much of this carbon dioxide enters the planet's atmosphere and swells the atmosphere's mass when Mars's tilt changes with its seasons, a NASA release said Thursday.

Collapse pits caused by dry ice sublimation and other clues suggest the deposit is in a dissipating phase, adding gas to the atmosphere each year, scientists say.

"We already knew there is a small perennial cap of carbon-dioxide ice on top of the water ice there, but this buried deposit has about 30 times more dry ice than previously estimated," said Roger Phillips of Southwest Research Institute in Boulder, Colo.

"When you include this buried deposit, Martian carbon dioxide right now is roughly half frozen and half in the atmosphere, but at other times it can be nearly all frozen or nearly all in the atmosphere," Phillips said.