NASA’s Mars Global Surveyor and Mars Odyssey missions
have provided evidence of a relatively recent ice age on
Mars. In contrast to Earth’s ice ages, a Martian ice age
waxes when the poles warm, and water vapor is transported
toward lower latitudes. Martian ice ages wane when the poles
cool and lock water into polar icecaps.

The “pacemakers” of ice ages on Mars appear to be much more
extreme than the comparable drivers of climate change on
Earth. Variations in the planet’s orbit and tilt produce
remarkable changes in the distribution of water ice from
Polar Regions down to latitudes equivalent to Houston or
Egypt. Researchers, using NASA spacecraft data and analogies
to Earth’s Antarctic Dry Valleys, report their findings in
Thursday’s edition of the journal Nature.

“Of all the solar system planets, Mars has the climate most
like that of Earth. Both are sensitive to small changes in
orbital parameters,” said planetary scientist Dr. James Head
of Brown University, Providence, R.I., lead author of the
study. “Now we’re seeing that Mars, like Earth, is in a
period between ice ages,” he said.

Discoveries on Mars, since 1999, of relatively recent water-
carved gullies, glacier-like flows, regional buried ice and
possible snow packs created excitement among scientists who
study Earth and other planets. Information from the Mars
Global Surveyor and Odyssey missions provided more evidence
of an icy recent past.

Head and co-authors from Brown (Drs. John Mustard and Ralph
Milliken), Boston University (Dr. David Marchant) and Kharkov
National University, Ukraine (Dr. Mikhail Kreslavsky)
examined global patterns of landscape shapes and near-surface
water ice the orbiters mapped. They concluded a covering of
water ice mixed with dust mantled the surface of Mars to
latitudes as low as 30 degrees, and is degrading and
retreating. By observing the small number of impact craters
in those features and by backtracking the known patterns of
changes in Mars’ orbit and tilt, they estimated the most
recent ice age occurred just 400 thousand to 2.1 million
years ago, very recent in geological terms. “These results
show Mars is not a dead planet, but it undergoes climate
changes that are even more pronounced than on Earth,” Head
said.

Marchant, a glacial geologist, who spent 17 field seasons in
the Mars-like Antarctic Dry Valleys, said, “These extreme
changes on Mars provide perspective for interpreting what we
see on Earth. Landforms on Mars that appear to be related to
climate changes help us calibrate and understand similar
landforms on Earth. Furthermore, the range of
microenvironments in the Antarctic Dry Valleys helps us read
the Mars record.”

Mustard said, “The extreme climate changes on Mars are
providing us with predictions we can test with upcoming Mars
missions, such as Europe’s Mars Express and NASA’s Mars
Exploration Rovers. Among the climate changes that occurred
during these extremes is warming of the poles and partial
melting of water at high altitudes. This clearly broadens the
environments in which life might occur on Mars.”

According to the researchers, during a Martian ice age, polar
warming drives water vapor from polar ice into the
atmosphere. The water comes back to ground at lower latitudes
as deposits of frost or snow mixed generously with dust. This
ice-rich mantle, a few meters thick, smoothes the contours of
the land. It locally develops a bumpy texture at human
scales, resembling the surface of a basketball, and also seen
in some Antarctic icy terrains. When ice at the top of the
mantling layer sublimes back into the atmosphere, it leaves
behind dust, which forms an insulating layer over remaining
ice. On Earth, by contrast, ice ages are periods of polar
cooling. The buildup of ice sheets draws water from liquid-
water oceans, which Mars lacks.

“This exciting new research really shows the mettle of NASA’s
‘follow-the-water’ strategy for studying Mars,” said Dr. Jim
Garvin, NASA’s lead scientist for Mars exploration. “We hope
to continue pursuing this strategy in January, if the Mars
Exploration Rovers land successfully. Later, the 2005 Mars
Reconnaissance Orbiter and 2007 Phoenix near-polar lander
will be able to directly follow up on these astounding
findings by Professor Head and his team.”

Global Surveyor has been orbiting Mars since 1997, Odyssey
since 2001. NASA’s Jet Propulsion Laboratory, a division of
the California Institute of Technology, Pasadena, manages
both missions for the NASA Office of Space Science,
Washington. Information about NASA’s Mars missions is
available on the Internet at: http://mars.jpl.nasa.gov