Steep Slopes on Mars Reveal Structure of Buried Ice
Researchers using NASA's Mars Reconnaissance Orbiter (MRO) have found eight sites where thick deposits of ice beneath Mars' surface are exposed in faces of eroding slopes.
Researchers using NASA's Mars Reconnaissance Orbiter (MRO) have
found eight sites where thick deposits of ice beneath Mars' surface are exposed
in faces of eroding slopes.These eight scarps, with slopes as steep as 55 degrees, reveal
new information about the internal layered structure of previously detected underground
ice sheets in Mars' middle latitudes.The ice was likely deposited as snow long ago. The deposits
are exposed in cross section as relatively pure water ice, capped by a layer one
to two yards (or meters) thick of ice-cemented rock and dust. They hold clues
about Mars' climate history. They also may make frozen water more accessible
than previously thought to future robotic or human exploration missions.Researchers who located and studied the scarp sites with the
High Resolution Imaging Science Experiment (HiRISE) camera on MRO reported the
findings today in the journal Science. The sites are in both northern and
southern hemispheres of Mars, at latitudes from about 55 to 58 degrees, equivalent
on Earth to Scotland or the tip of South America."There is shallow ground ice under roughly a third of the
Martian surface, which records the recent history of Mars," said the study's
lead author, Colin Dundas of the U.S. Geological Survey's Astrogeology Science
Center in Flagstaff, Arizona. "What we've seen here are cross-sections
through the ice that give us a 3-D view with more detail than ever before."Windows
into underground iceThe scarps directly expose bright glimpses into vast underground
ice previously detected with spectrometers on NASA's Mars Odyssey orbiter, with ground-penetrating radar instruments on MRO and on the European
Space Agency's Mars Express orbiter, and with observations of fresh impact
craters that uncover subsurface ice. NASA sent the Phoenix lander to Mars in
response to the Odyssey findings; in 2008, the Phoenix mission confirmed and
analyzed the buried water ice at 68 degrees north latitude, about one-third of
the way to the pole from the northernmost of the eight scarp sites.The discovery reported today gives us surprising windows
where we can see right into these thick underground sheets of ice," said
Shane Byrne of the University of Arizona Lunar and Planetary Laboratory,
Tucson, a co-author on today's report. "It's like having one of those ant
farms where you can see through the glass on the side to learn about what's
usually hidden beneath the ground."Scientists have not determined how these particular scarps initially
form. However, once the buried ice becomes exposed to Mars' atmosphere, a scarp
likely grows wider and taller as it "retreats," due to sublimation of
the ice directly from solid form into water vapor. At some of them, the exposed
deposit of water ice is more than 100 yards, or meter, thick. Examination of
some of the scarps with MRO's Compact Reconnaissance Imaging Spectrometer for
Mars (CRISM) confirmed that the bright material is frozen water. A check of the
surface temperature using Odyssey's Thermal Emission Imaging System (THEMIS)
camera helped researchers determine they're not seeing just thin frost covering
the ground.Researchers previously used MRO's Shallow Radar (SHARAD) to
map extensive underground water-ice sheets in middle latitudes of Mars and
estimate that the top of the ice is less than about 10 yards beneath the ground
surface. How much less? The radar method did not have sufficient resolution to say.
The new ice-scarp studies confirm indications from fresh-crater and neutron-spectrometer
observations that a layer rich in water ice begins within just one or two yards
of the surface in some areas.Astronauts'
access to Martian waterThe new study not only suggests that underground water ice
lies under a thin covering over wide areas, it also identifies eight sites
where ice is directly accessible, at latitudes with less hostile conditions
than at Mars' polar ice caps. "Astronauts could essentially just go there
with a bucket and a shovel and get all the water they need," Byrne said.The exposed ice has scientific value apart from its
potential resource value because it preserves evidence about long-term patterns
in Mars' climate. The tilt of Mars' axis of rotation varies much more than
Earth's, over rhythms of millions of years. Today the two planets' tilts are
about the same. When Mars tilts more, climate conditions may favor buildup of
middle-latitude ice. Dundas and co-authors say that banding and color
variations apparent in some of the scarps suggest layers "possibly
deposited with changes in the proportion of ice and dust under varying climate
conditions."This research benefited from coordinated use of multiple instruments
on Mars orbiters, plus the longevities at Mars now exceeding 11 years for MRO
and 16 years for Odyssey. Orbital observations will continue, but future
missions to the surface could seek additional information."If you had a mission at one of these sites, sampling the
layers going down the scarp, you could get a detailed climate history of Mars,"
suggested MRO Deputy Project Scientist Leslie Tamppari of NASA's Jet Propulsion
Laboratory, Pasadena, California. "It's part of the whole story of what
happens to water on Mars over time: Where does it go? When does ice accumulate?
When does it recede?"The University of Arizona operates HiRISE, which was built
by Ball Aerospace & Technologies Corp., Boulder, Colorado. The Johns
Hopkins University Applied Physics Laboratory, Laurel, Maryland, leads MRO's
CRISM investigation. The Italian Space Agency provided MRO's SHARAD instrument,
Sapienza University of Rome leads SHARAD operations, and the Planetary Science
Institute, based in Tucson, Arizona, leads U.S. involvement in SHARAD. Arizona
State University, Tempe, leads the Odyssey mission's THEMIS investigation. JPL,
a division of Caltech in Pasadena, California, manages the MRO and Odyssey projects
for the NASA Science Mission Directorate in Washington. Lockheed Martin Space, Denver,
built both orbiters and supports their operation.