Orbiting Camera Details Dramatic Wind Action on Mars

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster@jpl.nasa.gov

Lori Stiles 520-626-4402
University of Arizona, Tucson
lstiles@u.arizona.edu

NEWS RELEASE: 2008-111 Jan. 23, 2008

Orbiting Camera Details Dramatic Wind Action on Mars

Mars has an ethereal, tenuous atmosphere with less than one-percent the surface pressure
of Earth, which challenges scientists to explain complex, wind-sculpted landforms seen
with unprecedented detail in images from NASA's Mars Reconnaissance Orbiter.

One of the main questions has been if winds on present-day Mars are strong enough to
form and change geological features, or if wind-constructed formations were made in the
past, perhaps when winds speeds and atmospheric pressures were higher.

The eye-opening new views of wind-driven Mars geology come from the University of
Arizona's High Resolution Imaging Science Experiment camera (HiRISE). As the orbiter
flies at about 3,400 meters per second (7,500 mph) between 250 and 315 kilometers (155
to 196 miles) above the Martian surface, this camera can see features as small as half a
meter (20 inches).

"We're seeing what look like smaller sand bedforms on the tops of larger dunes, and,
when we zoom in more, a third set of bedforms topping those," said HiRISE co-
investigator Nathan Bridges of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"On Earth, small bedforms can form and change on time scales as short as a day."

There are two kinds of "bedforms," or wind-deposited landforms. They can be sand
dunes, which are typically larger and have distinct shapes. Or they can be ripples, in
which sand is mixed with coarser particles. Ripples are typically smaller and more linear.

HiRISE also shows detail in sediments deposited by winds on the downwind side of
rocks. Such "windtails" show which way the most current winds have blown, Bridges
said. They have been seen before, but only by rovers and landers, never by an orbiter.
Researchers can now use HiRISE images to infer wind directions over the entire planet.

Scientists discovered miles-long, wind-scoured ridges called "yardangs" with the first
Mars orbiter, Mariner 9, in the early 1970s. New HiRISE images reveal surface texture
and fine-scale features that are giving scientists insight into how yardangs form.
"HiRISE is showing us just how interesting layers in yardangs are," Bridges said. "For
example, we see one layer that appears to have rocks in it. You can actually see rocks in
the layer, and if you look downslope, you can see rocks that we think have eroded out
from that rocky layer above."

New images show that some layers in the yardangs are made of softer materials that have
been modified by wind, he added. The soft material could be volcanic ash deposits, or the
dried-up remnants of what once were mixtures of ice and dust, or something else. "The
fact that we see layers that appear to be rocky and layers that are obviously soft says that
the process that formed yardangs is no simple process but a complicated sequence of
processes," Bridges said.

"HiRISE keeps showing interesting things about terrains that I expected to be
uninteresting," said Alfred McEwen of the University of Arizona Lunar and Planetary
Laboratory, HiRISE principal investigator. "I was surprised by the diversity of
morphology of the thick dust mantles. Instead of a uniform blanket of smooth dust, there
are often intricate patterns due to the action of the wind and perhaps light cementation
from atmospheric volatiles."

Paul Geissler of the U.S. Geological Survey, Flagstaff, Ariz., has discovered from
HiRISE images that dark streaks coming from Victoria Crater probably consist of streaks
of dark sand blown out from the crater onto the surface. Scientists had wondered if wind
might have blown away lighter-colored surface material, exposing a darker underlying
surface. Geissler is comparing HiRISE images to images taken by NASA's Mars
Exploration Rover Opportunity rover at Victoria Crater.

Bridges is lead author and McEwen is a co-author on the paper titled "Windy Mars: A
dynamic planet as seen by the HiRISE camera" in Geophysical Research Letters in
December.

Information about the Mars Reconnaissance Orbiter spacecraft is online at

http://www.nasa.gov/mro . The mission is managed by JPL, a division of the California
Institute of Technology, Pasadena, for the NASA Science Mission Directorate,
Washington, D.C. Lockheed Martin Space Systems, Denver, is the prime contractor and
built the spacecraft. Ball Aerospace & Technologies Corp., Boulder, Colo., built the
HiRISE camera operated by The University of Arizona, Tucson.

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