The planet Mars we know today is a cold, dry, desert
world, but suppose the martian climate is changing even now,
year to year and decade to decade?

New observations by NASA’s Mars Global Surveyor spacecraft
are expanding understanding of the martian climate and may
indicate the climate is changing significantly even today.
This suggests even larger climate changes have occurred
during the planet’s recent history and may again in its
future. The observations were made during a full martian
year, 687 Earth days.

If this is so, Mars might someday become warmer and wetter,
as some scientists suggest it was during its early history.
Papers detailing these observations are published in the Dec.
7, 2001, issue of Science magazine.

“If the environment of Mars has really changed by as much and
over as short a time-scale as our observation implies, there
should be attributes of Mars reflecting these changes that
may be measurable by landers,” said Dr. Michael Malin,
principal investigator for Global Surveyor’s camera system at
Malin Space Science Systems, San Diego. “If Mars had a higher
atmospheric pressure in the not-too-distant past, it is more
likely that water was present as a liquid near the surface.”

Liquid water is required to support known forms of life, and
the presence of liquid water on Mars would make it more
likely life may once have existed there.

“Detecting evidence of climate change and variability on Mars
using Mars Global Surveyor data is an important aspect of
telling us where to go on the surface this decade,” said Dr.
James Garvin, NASA’s Lead Scientist for Mars Exploration,
Headquarters, Washington. “Clearly, the polar regions are a
good place where we would like to look for hydrothermal vents
to see if they exist on Mars.”

Images from Global Surveyor’s camera system show that pits —
often referred to as the “Swiss cheese” terrain — at the
southern polar ice cap of Mars have dramatically increased in
diameter, indicating the material has evaporated rapidly
compared to last year.

“The amount of change is much larger than any previous change
we’ve seen on Mars and it is much larger than can be
explained by the evaporation of water ice. We have calculated
the only material that could have changed this much is carbon
dioxide ice, what we know as dry ice,” said Malin. “This
means the Mars environment we see today may not be what it
was a few hundred years ago, and may not be what will exist a
few hundred years in the future.”

A separate observation is providing more detail about the
behavior of carbon dioxide in the martian atmosphere. Carbon
dioxide is a “greenhouse gas” believed to warm climates when
its atmospheric concentration increases. The spacecraft’s
laser altimeter and radio tracking system have made precise
measurements of the amount and density of carbon dioxide snow
in both polar regions. This information gives scientists the
first global measurement of the seasonal exchange of carbon
dioxide between the atmosphere and surface.

Due to the tilt of the planet, Mars has seasons just like
Earth. Scientists have long known the most important seasonal
change on Mars is the autumn and winter “freezing out” of
carbon dioxide from the atmosphere in the form of dry-ice
frost and snow. The evaporation of the surface frost in
spring and summer returns carbon dioxide to the atmosphere.
Over the course of a martian year, as much as a quarter of
the atmosphere freezes out, but until now scientists didn’t
know precisely where and how much dry-ice frost and snow
would pile up on the surface.

“We have measured how deep the dry-ice snow got on Mars over
the course of a year. We have also measured the corresponding
tiny change in the gravity field due to carbon dioxide being
transported from one pole to the other with the seasons,”
said Dr. Maria Zuber, deputy principal investigator of the
laser altimeter, at the Massachusetts Institute of
Technology, Cambridge, and NASA’s Goddard Space Flight
Center, Greenbelt, Md.

“Snow on Mars is denser than snow on Earth and is really more
like ice than snow. Understanding the present carbon dioxide
cycle is an essential step towards understanding past martian
climates,” Zuber said.

NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif.,
manages the Mars Global Surveyor mission for NASA’s Office of
Space Science, Washington. JPL is a division of the
California Institute of Technology, Pasadena.

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NOTE TO EDITORS: Images and additional information about
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    Extensive digital material is available at: