NASA Satellite Finds Interior of Mars is Colder

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Whitney Clavin 818-354-4673
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Dwayne Brown
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NEWS RELEASE: 2008-076 May 15, 2008

NASA Satellite Finds Interior of Mars is Colder

New observations from NASA's Mars Reconnaissance Orbiter indicate that the crust and upper
mantle of Mars are stiffer and colder than previously thought.

The findings suggest any liquid water that might exist below the planet's surface, and any
possible organisms living in that water, would be located deeper than scientists had suspected.

"We found that the rocky surface of Mars is not bending under the load of the north polar ice
cap," said Roger Phillips of the Southwest Research Institute in Boulder, Colo. Phillips is the
lead author of a new report appearing in this week's online version of Science. "This implies that
the planet's interior is more rigid, and thus colder, than we thought before."

The discovery was made using the Shallow Radar instrument on the spacecraft, which has
provided the most detailed pictures to date of the interior layers of ice, sand and dust that make
up the north polar cap on Mars. The radar images reveal long, continuous layers stretching up to
600 miles (1,000 kilometers), or about one-fifth the length of the United States.

"In our first glimpses inside the polar ice using the radar on Mars Reconnaissance Orbiter, we
can clearly see stacks of icy material that trace the history of Mars' climate," said Jeffrey Plaut of
NASA's Jet Propulsion Laboratory, Pasadena, Calif. Plaut is a science team member and a co-
author of the paper. "Radar has opened up a new avenue for studying Mars' past."

The radar pictures show a smooth, flat border between the ice cap and the rocky Martian crust.
On Earth, the weight of a similar stack of ice would cause the planet's surface to sag. The fact
that the Martian surface is not bending means that its strong outer shell, or lithosphere -- a
combination of its crust and upper mantle -- must be very thick and cold.

"The lithosphere of a planet is the rigid part. On Earth, the lithosphere is the part that breaks
during an earthquake," said Suzanne Smrekar, deputy project scientist for Mars Reconnaissance
Orbiter at JPL. "The ability of the radar to see through the ice cap and determine that there is no
bending of the lithosphere gives us a good idea of present day temperatures inside Mars for the
first time."

Temperatures in the outer portion of a rocky planet like Mars increase with depth toward the
interior. The thicker the lithosphere, the more gradually the temperatures increase. The discovery
of a thicker Martian lithosphere therefore implies that any liquid water lurking in aquifers below
the surface would have to be deeper than previously calculated, where temperatures are warmer.
Scientists speculate that any life on Mars associated with deep aquifers also would have to be
buried deeper in the interior.

The radar pictures also reveal four zones of finely spaced layers of ice and dust separated by
thick layers of nearly pure ice. Scientists think this pattern of thick, ice-free layers represents
cycles of climate change on Mars on a time scale of roughly one million years. Such climate
changes are caused by variations in the tilt of the planet's rotational axis and in the eccentricity of
its orbit around the sun. The observations support the idea that the north polar ice cap is
geologically active and relatively young, at about 4 million years.

On May 25, NASA's Phoenix Mars Lander is scheduled to touch down not far from the north
polar ice cap. It will further investigate the history of water on Mars, and is expected to get the
first up-close look at ice on the Red Planet.

The Shallow Radar instrument was provided by the Italian Space Agency, and its operations are
led by the InfoCom Department, University of Rome "La Sapienza." Thales Alenia Space Italia,
in Rome, is the Italian Space Agency's prime contractor for the radar instrument. Astro
Aerospace of Carpinteria, Calif., a business unit of Los Angeles-based Northrop Grumman
Corp., developed the instrument's antenna as a subcontractor to Thales Alenia Space Italia.

The Mars Reconnaissance Orbiter mission is managed by JPL for NASA's Science Mission
Directorate in Washington. Lockheed Martin Space Systems in Denver was the prime contractor
for the orbiter and supports its operations.

For more detailed information about the Mars Reconnaissance Orbiter, visit

http://www.nasa.gov/mro.

For more information about the Mars Phoenix Lander, visit

http://www.nasa.gov/phoenix .

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