NASA Orbiter Reveals Big Changes in Mars' Atmosphere

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster@jpl.nasa.gov

Maria Martinez 210-522-3305
Southwest Research Institute, San Antonio, Texas
maria.martinez@swri.org

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov

News release: 2011-123 April 21, 2011

NASA Orbiter Reveals Big Changes in Mars' Atmosphere

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-123&cid=release_2011-123

PASADENA, Calif. -- NASA's Mars Reconnaissance Orbiter 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 the orbiter'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 this week's issue of the journal Science.

The newly found deposit has a volume similar to Lake Superior's nearly 3,000 cubic miles (about
12,000 cubic kilometers). 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 the Mars Reconnaissance Orbiter'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 the Mars Reconnaissance Orbiter'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, a division of the California Institute of Technology in Pasadena, manages
the Mars Reconnaissance Orbiter 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 the Mars Reconnaissance Orbiter mission, visit
http://www.nasa.gov/mro .

-end-

To remove yourself from this mailing, please go to http://www.kintera.org/TR.asp?a=hrJJLZOEJaKLL8I&s=kkK2J7ONLgKOK6OTIuH&m=cqKRJ0OwEbKKJ3J

To remove yourself from all mailings from NASA Jet Propulsion Laboratory, please go to http://www.kintera.org/TR.asp?a=kuLPI8PQIdJSJiL&s=kkK2J7ONLgKOK6OTIuH&m=cqKRJ0OwEbKKJ3J