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September
24, 2009: Meteorites recently striking Mars have
exposed deposits of frozen water not far below the Martian
surface. Pictures of the impact sites taken by NASA's Mars
Reconnaissance Orbiter show that frozen water may be available
to explorers of the Red Planet at lower latitudes than previously
thought.
"This
ice is a relic of a more humid climate from perhaps just several
thousand years ago," says Shane Byrne of the University
of Arizona, Tucson.
Byrne
is a member of the team operating the orbiter's High Resolution
Imaging Science Experiment, or HiRISE camera, which captured
the unprecedented images. Byrne and 17 co-authors report the
findings in the Sept. 25 edition of the journal Science.
Above:
A fresh, 6-meter-wide, 1.33-meter-deep crater on Mars photographed
on Oct. 18, 2008, and again on Jan. 14, 2009, by Mars Reconnaissance
Orbiter's HiRISE camera. The bright material is ice, which
fades from Oct. to Jan. because of sublimation and obscuration
by settling dust. [more]
"We now know we can use new impact sites as places to
look for ice in the shallow subsurface," adds Megan Kennedy
of Malin Space Science Systems in San Diego, a co-author of
the paper and member of the team operating the orbiter's Context
Camera.
So
far, the camera team has found bright ice exposed at five
Martian sites with new craters that range in depth from approximately
half a meter to 2.5 meters (1.5 feet to 8 feet). The craters
did not exist in earlier images of the same sites. Bright
patches darkened in the weeks following initial observations,
as freshly exposed ice vaporized into the thin Martian atmosphere.
The
finds indicate water-ice occurs beneath Mars' surface halfway
between the north pole and the equator, a lower latitude than
expected in the dry Martian climate.
During
a typical week, the spacecraft's Context Camera returns more
than 200 images of Mars that cover a total area greater than
California. The camera team examines each image, sometimes
finding dark spots that fresh, small craters make in terrain
covered with dust. Checking earlier photos of the same areas
can confirm a feature is new. In this way, the team has found
more than 100 fresh impact sites.
 An
image from the camera on Aug. 10, 2008, showed apparent cratering
that occurred after an image of the same ground was taken
67 days earlier. The opportunity to study such a fresh impact
site prompted a look by the orbiter's higher resolution camera
on Sept. 12, 2009, confirming a cluster of small craters.
Right:
The patch of ice exposed at this late-2008 crater was large
enough for the orbiter's spectrometers to take readings and
confirm that it is H2O. [more]
"Something
unusual jumped out," Byrne said. "We observed bright
material at the bottoms of the craters with a very distinct
color. It looked a lot like ice."
The
bright material at that site did not cover enough area for
a spectrometer instrument on the orbiter to determine its
composition. "Was it really ice?" the team wondered.
The answer came from another crater with a much larger area
of bright material.
"We
were excited [when we saw it], so we did a quick-turnaround
observation," said co-author Kim Seelos of Johns Hopkins
University Applied Physics Laboratory in Laurel, Md. "Everyone
thought it was water-ice, but it was important to get the
spectrum for confirmation."
Mars
Reconnaissance Orbiter Project Scientist Rich Zurek, of NASA's
Jet Propulsion Laboratory, Pasadena, Calif., said, "This
mission is designed to facilitate coordination and quick response
by the science teams. That makes it possible to detect and
understand rapidly changing features."
Above:
This map shows five locations where fresh impact cratering
has excavated water ice from just beneath the surface of Mars
(sites 1 through 5) and the Viking Lander 2 landing site (VL2),
in the context of color coding to indicate estimated depth
to ice. [more]
The
ice exposed by fresh impacts suggests that NASA's Viking Lander
2, digging into mid-latitude Mars in 1976, might have struck
ice if it had dug only 10 centimeters (4 inches) deeper. The
Viking 2 mission, which consisted of an orbiter and a lander,
launched in September 1975 and became one of the first two
space probes to land successfully on the Martian surface.
The Viking 1 and 2 landers characterized the structure and
composition of the atmosphere and surface. They also conducted
on-the-spot biological tests for life on another planet.
To
view images of the craters and learn more about the Mars Reconnaissance
Orbiter visit http://www.nasa.gov/mro.
Editor: Dr.
Tony Phillips | Credit: Science@NASA
| more
information |
| Mars
Reconnaissance Orbiter -- home page
NASA's
Jet Propulsion Laboratory in Pasadena manages the Mars
Reconnaissance Orbiter for NASA's Science Mission Directorate
in Washington. Lockheed Martin Space Systems in Denver
built the spacecraft. The Context Camera was built and
is operated by Malin Space Science Systems. The University
of Arizona operates the HiRISE camera, which Ball Aerospace
& Technologies Corp., in Boulder, Colo., built.
The Johns Hopkins University Applied Physics Laboratory
led the effort to build the Compact Reconnaissance Imaging
Spectrometer and operates it in coordination with an
international team of researchers.
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