- New observations by NASA's Mars Global Surveyor
spacecraft
indicate that the climate on Mars is changing significantly -- suggesting
that the planet underwent a large climate change in the past and may do
so again in the future.
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- If that's the case, Mars might someday become warmer
and wetter, as some scientists suggest it was during its early
history.
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- The Global Surveyor observations were made during a full
Martian year, equal to 687 Earth days.
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- "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 Michael Malin, principal investigator for Global
Surveyor's camera system at Malin Space Science Systems, San Diego.
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- "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," he said.
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- That could hold important implications in the search
for life since liquid water is required to support known forms of life.
The presence of liquid water on Mars would make it more likely that life
may once have existed there.
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- "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 Jim Garvin, NASA's
lead scientist for Mars exploration. "Clearly, the polar regions are
a good place where we would like to look for hydrothermal vents to see
if they exist on Mars."
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- 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.
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- "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.
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- "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."
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- 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.
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- 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.
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- This information gives scientists the first global
measurement
of the seasonal exchange of carbon dioxide between the atmosphere and
surface.
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- 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.
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- The evaporation of the surface frost in spring and summer
returns carbon dioxide to the atmosphere.
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- 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.
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- "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 Maria Zuber, deputy
principal investigator of the laser altimeter, at the Massachusetts
Institute
of Technology in Cambridge, and NASA's Goddard Space Flight Center in
Greenbelt,
Md.
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- "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,"
she said.
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