This cross-section view of underground layers near Mars' south pole is a radargram based on data from NASA's MRO. Researchers interpret the zone that is nearly free of radio-wave reflections to be composed of frozen carbon dioxide, or 'dry ice'.
Credit: NASA/JPL-Caltech/Sapienza University of Rome/Southwest Research Institute
MOFFETT FIELD: The south pole of Mars is home to 30 times more dry ice than previously believed, suggesting that the red planet was once a much wetter place, NASA scientists have found.
The total amount of atmosphere on Mars changes dramatically as the tilt of the planet's axis varies, which can affect the stability of liquid water if it exists on the Martian surface and increase the frequency and severity of Martian dust storms.
Researchers using NASA's Mars Reconnaissance Orbiter’s (MRO) ground-penetrating radar identified a large, buried deposit of frozen carbon dioxide, or dry ice, at the Red Planet's south pole.
The scientists suspect that much of this carbon dioxide enters the planet's atmosphere and swells the atmosphere's mass when Mars' tilt increases. “The results add to a growing pile of evidence suggesting that long ago, ancient Mars had a thicker, carbon dioxide-filled atmosphere and flowing bodies of water," said the study in Science.
30 times more than estimated
The newly found deposit has a volume similar to Lake Superior's nearly 3,000 cubic miles. The deposit holds up to 80% as much carbon dioxide as today's Martian atmosphere.
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. Mars' atmosphere is about 95% carbon dioxide, in contrast to Earth's much thicker atmosphere, which is less than .04% carbon dioxide.
"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. Phillips is deputy team leader for MRO's Shallow Radar instrument and lead author of the report.
Identifying the dry ice deposit
"We identified the deposit as dry ice by determining the radar signature fit the radio-wave transmission characteristics of frozen carbon dioxide far better than the characteristics of frozen water," said co-author Roberto Seu of Sapienza University of Rome, team leader for the Shallow Radar.
Additional evidence came from correlating the deposit to visible sublimation features typical of dry ice.
"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.
