Topic Name: Observations give precise estimate of Mars surface ice
Category: Geo sciences & technology
Research persons: Professor Maria Zuber
Location: 77 Massachusetts Ave, Cambridge, MA 02139-4307, United States
An MIT-led team of planetary scientists has found that the southern pole of Mars
contains the largest deposit of frozen water in the
solar system, outside of Earth.
The new results show that water, not carbon dioxide, is the predominant frozen
liquid found in the
region of Mars, said Maria Zuber, MIT professor of geophysics.
Zuber said scientists have suspected that the southern polar cap of Mars is
comprised of a thin veneer of carbon dioxide that rests atop a layer of dust and
ice. However, scientists have also observed a surrounding area much larger than
the polar cap that is dark and smooth, and it was uncertain whether that region
was also composed of dust or ice--or both.
"What we found is that water ice is the dominant constituent beneath a thin dust
veneer," said Zuber, lead author of a paper on the work appearing in the Sept.
21 issue of Science. Ever since carved channels were first observed on the
surface of Mars, scientists have suspected that water once flowed across the
Scientists also wondered whether the Martian poles held large reserves of water.
However, because the Mars atmosphere is 95 percent carbon dioxide with only
trace amounts of water, some researchers theorized that the polar caps were
frozen carbon dioxide, or dry ice.
Zuber's team identified the composition of the southern polar cap by calculating
its density. Their results show the density of the polar cap as well as the
surrounding smooth layered deposit region is about 1,220 kilograms per cubic
meter, which indicates that it is made of mostly water, with about 15 percent
silicate dust mixed in.
(The density of water ice is 1,000 kilograms per cubic meter, and the density of
dry ice is 1,600 kilograms per cubic meter.)
Zuber and her colleagues used topographical and gravitational data gathered by
three Mars orbiters to find the volume and mass of the ice cap, allowing them to
calculate its density.
"It's a really simple experiment but you have to measure things very precisely,"
Zuber said, who is head of MIT's Department of Earth, Atmospheric, and
The experiment reveals that the southern Martian polar region is the largest
body of frozen water on the planet and the largest, outside of Earth, in the
inner solar system, which includes Mars, Earth, Venus and Mercury.
Until now, scientists were puzzled by the observation that a large percentage of
the southern polar region surface does not reflect much light, as it would if
there were ice on the surface. This study shows that much of the ice is covered
in a layer of dust, but it remains unknown why the dust only covers certain
areas, Zuber said.
She plans to undertake a similar density study of the northern polar cap, which
does not appear to have a covering of dust, but which is abuts against a large
apparent dune field that is not now thought to contain significant ice.
Zuber is the lead investigator for gravity for the
Mars Reconnaissance Orbiter,
and deputy principal investigator for the altimetry experiment aboard the Mars
Global Surveyor. The team also used data from the Mars Odyssey satellite.
Such collaborations between teams "really increase the value of what any single
experiment could show on its own," Zuber said.
Jeffrey Andrews-Hanna, an MIT postdoctoral associate in the Department of Earth,
Atmospheric and Planetary Sciences, is also an author on the paper. Other
authors are Roger Phillips of Washington University; Sami Asmar, Alexander
Konopliv, Jeffrey Plaut and Suzanne Smrekar of the Jet Propulsion Laboratory at
Caltech; and Frank Lemoine and David Smith of the Planetary Geodynamics
Laboratory at the NASA Goddard Space Flight Center.
About Researchers & Contacts:
E. A. Griswold Professor of Geophysics
Head of the Department
Ph.D., 1986, Brown University
Dept. of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology
77 Massachusetts Ave.
Cambridge, MA 02139-4307 USA
Theoretical modeling of geophysical processes; analysis of altimetry, gravity
and tectonics to determine the structure and dynamics of the Earth and solid
planets; development and implementation of spacecraft laser and radio tracking
Short Note About Geo Sciences:
The Directorate for Geosciences (GEO) is one of six research arms within the
National Science Foundation. Its mission is to support research in the
atmospheric, earth, and ocean sciences. As the principal source of federal
funding for university-based fundamental research in the geosciences, GEO
addresses the nation's need to understand, predict, and respond to environmental
events and changes to use Earth's resources wisely. Basic research in the
geosciences advances scientific knowledge of Earth's environment, including
resources such as water, energy, minerals, and biological diversity.
GEO-supported research also advances our ability to predict natural phenomena of
economic and human significance, such as climate changes, weather, earthquakes,
fish-stock fluctuations, and disruptive events in the solar-terrestrial
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