Press Release

Odyssey Thermal Data Reveals a Changing Mars

By SpaceRef Editor
June 5, 2003
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Odyssey Thermal Data Reveals a Changing Mars

The first overview analysis of a year’s worth of high-resolution
infrared data gathered by the Thermal Emission Imaging System (THEMIS)
on NASA’s Mars Odyssey spacecraft is opening Mars to a new kind of
detailed geological analysis and revealing a dynamic planet that has
experienced dramatic environmental change.

The report by THEMIS’s science team will appear in an upcoming issue of
Science and will be released on June 5 in the magazine’s online preview,
Science Express.

“THEMIS is creating a set of data that is going to revolutionize our
mapping of the planet and our idea of the planet’s geology,” said lead
author and THEMIS Principal Investigator Philip Christensen, Korrick
Professor of Geological Sciences at Arizona State University. “It will
keep Mars scientists busy for the next 20 years trying to understand the
processes that have produced this landscape.”

THEMIS is providing planetary geologists with detailed temperature and
infrared radiation images of the martian surface. The images reveal
geological details that were impossible to detect even with the
high-resolution Mars Orbital Camera on NASA’s Mars Global Surveyor and
that have 300 times higher resolution than MGS’s Thermal Emission
Spectrometer. Among the significant findings noted in the report is the
detection of layers in the martian surface that indicate major changes
in past environmental conditions.

“With a visible light camera, I can take a picture of a lava flow, but
even with the highest resolution cameras that we have today the smallest
thing we can see is the size of a bus and in order to do geology I need
to have more detail,” said Christensen.

“The camera on Mars Global Surveyor takes exquisite images that show
layers, but it doesn’t tell me anything about composition – is it a
layer of boulders with a layer of sand on top? I have no way of knowing.
With the THEMIS temperature data, I can actually get an idea because the
layers vary – and each layer has remarkably different physical

Daytime and nighttime temperature data can allow scientists to
distinguish between solid rock and a variety of loose materials, from
boulders to sand and dust. As any beach-goer knows, fine-grained sand
heats up more rapidly at the surface than solid stone (which transmits
more heat inward) but it also cools off more rapidly at night, when
solid materials retain heat.

“We have seen layers, each with dramatically different physical
properties, in places like Terra Meridiani,” Christensen said. “Why do
the physical properties in the different layers change? They change
because the environment in which those rocks were deposited changed.

“It’s very difficult to say exactly what happened in any particular
place, but what we’ve found is that in many places on Mars it hasn’t
just been the same old thing happening for year after year for billions
of years. These data have been so remarkable and so different from all
of our previous experience that it has taken time to sift through the
images and figure out what we’re seeing.”

Among the details that have stood out so far are kilometer-wide
stretches of bare bedrock that Christensen notes were unexpected, given
the Mars’ known dustiness. Large areas of exposed rock indicate that
strong environmental forces are currently at work, “scouring” from the
surface any past sediment as well as any new material that might be
falling from the atmosphere.

Also unexpected is the finding that accumulations of loose rock are
common on martian hillsides, indicating recent processes of weathering
continuing to affect the planet. ” If those rocks had been made a
billion years ago, they’d be covered with dust,” Christensen pointed
out. “This shows a dynamic Mars – it’s an active place.”

However, despite Odyssey’s past findings of significant martian ice
deposits, there are also indications that, in many places on the
planet, water may not be one of the active causes behind the observed
geological features.

Analyzing the spectra from the ten different bands of infrared light the
instrument can detect, the THEMIS team has begun to identify specific
mineral deposits, including a significant layer of the mineral olivine
near the bottom of a four-and-a-half kilometer deep canyon known as
Ganges Chasma. Olivine, Christensen notes, is significant because it
decomposes rapidly in the presence of water.

“This gives us an interesting perspective of water on Mars,” he said.
“There can’t have been much water – ever — in this place. If there was
groundwater present when it was deep within the surface, the olivine
would have disappeared. And since the canyon has opened up, if there
had ever been water at the surface it would be gone too. This is a very
dry place, because it’s been exposed for hundreds of millions of years.
We know that some places on Mars have water, but here we see that some
really don’t.”

Overall, Christensen notes that the emerging diversity and complexity of
the planet point to the likelihood of future surprises and keep
enlarging the possibilities for discovery on Mars.

“With Odyssey, we are looking at Mars in its entirety, in context. It’s
remarkable how much this has already changed our view of the complexity
and richness of the planet. We discovered that it has a really dynamic
geologic history. It has far more ice and water than we thought — we’re
seeing snow and gullies, layers – and there are also processes involving
volcanoes, impact craters and wind. It’s a fascinating place.”

In addition to Christensen, the authors on the paper include Joshua L.
Bandfield, James F. Bell, Noel Gorelick, Victoria E. Hamilton, Anton
Ivanov, Bruce M. Jakosky, Hugh H. Kieffer, Melissa D. Lane, Michael C.
Malin, Timothy McConnochie, Alfred S. McEwen, Harry Y. McSween, Greg L.
Mehall, Jeffery E. Moersch, Kenneth H Nealson, James W. Rice, Mark I.
Richardson, Steven W. Ruff, Michael D. Smith, Timothy N. Titus, and
Michael B Wyatt.

The Jet Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the 2001 Mars Odyssey mission for NASA’s
Office of Space Science in Washington. Investigators at Arizona State
University in Tempe, the University of Arizona in Tucson and NASA’s
Johnson Space Center, Houston, operate the science instruments.
Additional science partners are located at the Russian Aviation and
Space Agency and at Los Alamos National Laboratories, New Mexico.
Lockheed Martin Astronautics, Denver, is the prime contractor for the
project, and developed and built the orbiter. Mission operations are
conducted jointly from Lockheed Martin and from JPL. Additional
information about the 2001 Mars Odyssey is available on the Internet at:

SpaceRef staff editor.