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OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA. TELEPHONE (2l3) 354-50ll
FOR RELEASE: Wednesday, June l, l977
A large reservoir of carbon dioxide trapped in the
soil
of Mars may account for apparent drastic changes in the red
planet's
climate over billions of years, two scientists at Caltech's
Jet
Propulsion Laboratory told their colleagues today.
Dr. Fraser P. Fanale and W. A. Cannon told a
meeting of
the American Geophysical Union in Washington, D.C., that
exchange
of carbon dioxide between the Martian regolith -- a layer of
soil
up to l kilometer (0.62 miles) thick -- and the Martian
atmosphere
may be the key to climate changes on Mars -- from warm and
wet in the past to the planet's present ice age.
"Our results suggest," Fanale said, "that the
regolith
acts as a sort of 'sponge' for large amounts of carbon
dioxide
that are expelled into the atmosphere during warm epochs and
return
to the regolith during cold epochs."
A variety of evidence points to a denser atmosphere
in
Mars' past -- primarily deeply carved water channels on the
surface.
îBut water cannot flow in large amounts for any length of time
on
Mars under current conditions; the atmosphere is too thin and
temperatures are too cold to allow water to remain on the
surface
as a liquid.
In the past, scientists answered the problem by
proposing
that the residual polar caps on Mars -- those parts that
remain
frozen through the summer months -- were huge reservoirs of
frozen carbon dioxide. When small changes in the Martian
orbit,
or changes in the sun's output, heated the planet, so the
theory
went, these polar caps thawed and the carbon dioxide went
into
the atmosphere. Most investigators agree that, if enough CO2
were
supplied to the atmosphere, a transition to a "warm-wet"
climate
would be likely.
However, results from Mariner 9 and from Viking
showed
that the residual (or permanent) polar caps are not frozen
carbon
dioxide, but are frozen water. That would not permit the
atmosphere
to build to the density required to allow large quantities of
liquid water on the surface, Fanale and Cannon agree.
They suggest in their AGU paper that the thick soillayer
or regolith could provide enough presently hidden but
exchangeable
CO2 to "pump up" the atmosphere in response to changes in the
amount of solar energy reaching the surface.
Their studies of C02 adsorption by pulverized rocks
suggest that the soil on Mars can absorb very large
quantities
of carhon dioxide in much the same way as charcoal adsorbs
odorous gases in a refrigerator.
Further, they say, the carbon dioxide thus held in
the
Martian soil is exchangable with the atmosphere: once the
regolith
warms up, the carbon dioxide can be released into the
atmosphere.
When the regolith cools again the carbon dioxide is adsorbed
again.
Although carbon dioxide may exist in the form of
carbonate
rocks in the regolith, Fanale and Cannon say, it is not
usable
-more-
in the exchange process, since it is chemically bound in the
rocks;
simple warming of the regolith will not free it.
The Fanale-Cannon exchange process needs between
100,000
and 1 million years to release all the CO2, since it probably
takes that long to warm the regolith to the suggested depth
of
î1 kilometer.
In this model, they say, it appears that all
essential
ingredients for development of a definitive Mars
climate-change
model are available. The validity of climate changes on Mars
need not be doubted, Fanale and Cannon say, just because no
apparent large C02 reservoir is identifiable at the polar
caps.
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