NASA's Mars Global Surveyor and Mars Odyssey missions have
provided evidence of a recent ice age on Mars. In contrast to
Earth's ice ages, a martian ice age waxes when the poles warm up and
water vapor is transported toward lower latitudes. Martian ice
ages wane when the poles cool and lock water into polar icecaps.
|This simulated view shows Mars as it might have appeared during the height of a possible ice age in geologically recent time. Credit: NASA
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 the Thursday, Dec. 18 edition of the
"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."
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 his 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
mapped by the orbiters. They concluded that a covering of water ice
mixed with dust mantled the surface of Mars to latitudes as low as
30 degrees, and is now 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 400,000 to 2.1
million years ago, very recent in geological terms. "These results
show that 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 has 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
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 or yards 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, D.C.
NASA's Mars missions is available on the Internet at: