Sharp views show ground ice on Mars is patchy and variable (Forwarded)

Arizona State University
College of Liberal Arts and Sciences
School of Earth and Space Exploration
Tempe, Arizona

MEDIA CONTACTS:
Robert Burnham, (480) 458-8207
Carol Hughes, (480) 965-6375

SOURCE:
Joshua Bandfield, (480) 965-0601

May 2, 2007

Sharp views show ground ice on Mars is patchy and variable

For the first time, scientists have found that water ice lies at variable
depths over small-scale patches on the Red Planet. The discovery draws a
much more detailed picture of underground ice on Mars than was previously
available. The new results appear in the May 3, 2007, issue of the
scientific journal Nature.

"We find the top layer of soil has a huge effect on the water ice in the
ground," says Joshua Bandfield, a research specialist in Arizona State
University's School of Earth and Space Exploration and sole author of the
paper. His findings come from data sent back to Earth by the Thermal
Emission Imaging System (THEMIS) on NASA's Mars Odyssey orbiter.

THEMIS is a sophisticated camera that takes images in 5 visual bands and
10 heat-sensing (infrared) ones. At infrared wavelengths, the smallest
details THEMIS can see on the surface are 330 feet (100 meters) wide.

The new results were made using infrared images of several Martian sites,
each at a latitude of 60 to 70 degrees, north and south. "These sites are
in regions where subsurface water ice is known to exist," Bandfield says.

THEMIS' Sharp View

He explains that water ice lying at shallow depths was first detected and
mapped by the Gamma Ray Spectrometer (GRS) suite of instruments, also on
Mars Odyssey. But, as Bandfield notes, "the smallest patches detectable by
GRS are 300 miles, or 500 kilometers, wide." The new work shows that
THEMIS' heat-sensing capability gives scientists a much sharper tool to
hunt for buried ice.

"Scientists have known for more than a decade that water is on Mars,
mostly in the form of ice," says Philip Christensen of ASU's Mars Space
Flight Facility. Christensen, a Regents' Professor of geological sciences
at ASU, designed THEMIS but did not participate in this research. "What's
exciting is finding out where the ice is in detail and how it got there.
We've reached the next level of sophistication in our questions."

Christensen adds, "GRS can probe a meter deep, but it has a giant
footprint. Most infrared spectrometers can detect surface ice and ice a
few fractions of a millimeter down. THEMIS is sensitive to thermal waves
which can penetrate several inches deep -- and it can spot details the
size of a football field."

Seeking Warmth

Bandfield's approach used THEMIS as a thermometer to measure how fast the
ground changed temperature during local spring, summer, and fall at the
sites. The nature of the surface soil, he says, "makes a big difference in
how deep the ice is."

Areas with many rocks at the surface, Bandfield explains, "pump a lot of
heat into the ground and increase the depth where you'll find stable ice."
In contrast, he says, dusty areas tend to insulate the ice, allowing it to
survive closer to the surface. "These two surface materials -- rock and
dust -- vary widely across the ground, giving underground ice a patchy
distribution."

Computer models helped him interpret the temperature observations, he
says. "They show areas where water ice would be only an inch or so under
the soil, while in other areas ice could lie many feet below the surface."

Mars Climate Cycles

Bandfield notes the results fit long-term climatic models for Mars. These
show the planet has been both warmer and colder in the past, similar to
glacial cycles on Earth.

He says, "The fact that ice is present near the depth of stability in the
current Martian climate shows that the ground ice is responding to climate
cycles." In turn, he adds, this implies that water ice in the ground can
swap places with water vapor in the atmosphere as the climate changes.

Bandfield concludes, "The THEMIS measurements support an active water
cycle on Mars such as other research has predicted."

"This work has improved our understanding of the water cycle as part of
the ongoing exploration of Mars," says Christensen.

Phoenix: Hunting For Ice

In August 2007, NASA will launch Phoenix, a mission designed to sample
Martian ground ice directly. The Phoenix spacecraft is a non-roving lander
that will go to a high-latitude site in Mars' northern hemisphere. Upon
landing, it will expose buried ice by scraping away the soil. After
collecting a sample of icy soil, Phoenix will analyze its qualities as a
possible habitat for microbial life.

Says Bandfield, "The take-home message for the Phoenix lander is that the
THEMIS results show a lot of patchiness in the ground ice, and this should
continue down to smaller and smaller scales."

Phoenix, he adds, "may find ground ice is shallower and much easier to
reach in some spots than in others."

[NOTE: Images supporting this release are available at
http://themis.asu.edu/news-groundice ]