MRO Reveals Dramatic Changes In Mars' Atmosphere
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Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne....@nasa.gov
Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.w...@jpl.nasa.gov
Maria Martinez
Southwest Research Institute, San Antonio, Texas
210-522-3305
maria.m...@swri.org
RELEASE: 11-118
NASA SPACECRAFT REVEALS DRAMATIC CHANGES IN MARS' ATMOSPHERE
WASHINGTON -- NASA's Mars Reconnaissance Orbiter (MRO) has discovered
the total amount of atmosphere on Mars changes dramatically as the
tilt of the planet's axis varies. This process 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 MRO's 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 findings are published in a
report in the journal Science.
The newly found deposit has a volume similar to Lake Superior's nearly
3,000 cubic miles. The deposit holds up to 80 percent 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 percent carbon dioxide, in contrast to Earth's
much thicker atmosphere, which is less than .04 percent 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.
"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 Roberto Seu of Sapienza University of Rome, team leader for the
Shallow Radar and a co-author of the new report.
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.
An occasional increase in the atmosphere would strengthen winds,
lofting more dust and leading to more frequent and more intense dust
storms. Another result is an expanded area on the planet's surface
where liquid water could persist without boiling. Modeling based on
known variation in the tilt of Mars' axis suggests several-fold
changes in the total mass of the planet's atmosphere can happen on
time frames of 100,000 years or less.
The changes in atmospheric density caused by the carbon-dioxide
increase also would amplify some effects of the changes caused by the
tilt. Researchers plugged the mass of the buried carbon-dioxide
deposit into climate models for the period when Mars' tilt and
orbital properties maximize the amount of summer sunshine hitting the
south pole. They found at such times, global, year-round average air
pressure is approximately 75 percent greater than the current level.
"A tilted Mars with a thicker carbon-dioxide atmosphere causes a
greenhouse effect that tries to warm the Martian surface, while
thicker and longer-lived polar ice caps try to cool it," said
co-author Robert Haberle, a planetary scientist at NASA's Ames
Research Center in Moffett Field, Calif. "Our simulations show the
polar caps cool more than the greenhouse warms. Unlike Earth, which
has a thick, moist atmosphere that produces a strong greenhouse
effect, Mars' atmosphere is too thin and dry to produce as strong a
greenhouse effect as Earth's, even when you double its carbon-dioxide
content."
The Shallow Radar, one of MRO's six instruments, was provided by the
Italian Space Agency and its operations are led by the Department of
Information Engineering, Electronics and Telecommunications at
Sapienza University of Rome. NASA's Jet Propulsion Laboratory in
Pasadena, Calif., manages the MRO project for NASA's Science Mission
Directorate at the agency's headquarters in Washington. Lockheed
Martin Space Systems in Denver built the spacecraft.
For more information about MRO, visit:
http://www.nasa.gov/mro
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