 | VIEW
INSIDE MARS REVEALS RAPID COOLING AND BURIED CHANNELS |  |
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| | | Mars
Interior | | | By
combining highly accurate topographic maps with new plots of the planet’s
gravitational field, researchers have developed a working draft of what the planet’s
interior looks like several kilometers below the surface. This map shows the "moho",
the area where the planet’s crust borders its mantle.
Some
of Mars' best kept secrets, long buried beneath the surface of the red planet,
were recently revealed by instruments on NASA's Mars Global Surveyor spacecraft.
New
observations of Mars reveal that the planet's flat northern lowlands were an early
zone of high heat flow that later may have been the site of rapid water accumulation,
according to a view of the Martian interior generated using data from Mars Global
Surveyor (MGS). Elevation and gravity measurements, which have been used to probe
beneath the surface of Mars, indicate a period of rapid cooling early in Martian
history, and evidence for large, buried channels that could have formed from the
flow of enormous volumes of water. This
global view of the Martian interior was generated from gravity measurements with
the Radio Science experiment and elevation measurements from the Mars Orbiter
Laser Altimeter (MOLA) instruments. Gravity and topography measurements were combined
to reveal the structure of the crust on Mars, which preserves the record of melting
of the interior and the heat loss from the planet over time. "The
crustal thickness map shows that, as for Earth, Mars has two distinct crustal
provinces," explained Dr. Maria Zuber of the Massachusetts Institute of Technology,
Cambridge, MA, and lead author of a study to be published in the March 10 issue
of Science. Beneath the rough southern highlands and Tharsis volcanic province
the crust, estimated at 50 miles thick, thins progressively from the South pole
toward the North. In contrast, the northern lowlands and Arabia Terra region of
the southern highlands have a crust of uniform thickness, about 22 miles deep.
The
crustal structure accounts for the elevation of the Martian northern lowlands,
which controlled the northward flow of water early in Martian history, producing
a network of valleys and outflow channels. The new gravity-field data suggest
that the transport of water continued far into the northern plains. The gravity
shows features interpreted as channels buried beneath the northern lowlands emanating
from Valles Marineris and the Chryse and Kasei Valles outflow regions. The
features are about 125 miles wide and over a thousand miles long, with characteristics
that can be explained by water flow on the surface or in a submarine environment,
later buried by sediments. The large size of these channels implies that any bodies
of water in the northern lowlands could have accumulated rapidly. The now-buried
channels may represent the means for filling an early ocean.
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| | | Mars
Channel | | | Evidence
suggests that rapid heat flow in the Northern Hemisphere produced a wide lowland
area, encouraging the formation of channels, which could have sluiced water resources
into a large basin, even an early ocean. Shown in this image is one such channel,
draining from the giant Valles Marineris into the wide, flat area of the north.
The
gravity and topography also provide information on the cooling of Mars over time,
which bears on the early climate and history of water. "The observations
suggest that the northern lowlands was a location of high heat loss from the interior
early in Martian history, probably due to a period of vigorous convection and
possibly plate recycling inside of Mars," said Dr. Sean Solomon, Director
of the Department of Terrestrial Magnetism of the Carnegie Institution in Washington,
DC, and a co-author of the study. The
high heat-loss zone corresponds to the part of Mars proposed to have been the
site of an ancient ocean. The rapid transport of heat to the surface in this region
would have released onto the surface and into the atmosphere gases and water or
ice trapped in the interior. The time of rapid interior heat loss may correspond
to the period when Mars had a warmer climate, liquid water flowed on the surface,
and the planet's surface was shielded from the solar wind by a global magnetic
field. During
the ongoing Mars Global Surveyor mapping mission the Radio Science and MOLA experiments
will continue to collect data on a near-continuous basis through the end of the
mission in February 2001. The MOLA instrument was designed and built by the Laser
Remote Sensing Branch of the Laboratory for Terrestrial Physics at NASA's Goddard
Space Flight Center, Greenbelt, MD. The Radio Science experiment is implemented
from the Center for Radio Astronomy of Stanford University, Palo Alto, CA. The
Mars Global Surveyor mission is managed for NASA's Office of Space Science, Washington,
DC, by the Jet Propulsion Laboratory, Pasadena, CA, a division of the California
Institute of Technology. Back
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