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By Andrew Bridges Pasadena Bureau Chief Space.Com
PASADENA,
Calif. -- NASA has released a quartet of Martian images
that show several of the Red Planet’s numerous craters
patched with snow-white frost.
The
American space agency’s Mars Global Surveyor orbiter
captured the images as part of its ongoing monitoring of
the seasonal advance and retreat of polar frosts on the
planet’ s surface.
The
four images render wide-angle views of four distinct craters
-- two each in Mars' northern and southern hemispheres.
They are located the middle polar latitudes of each hemisphere.
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Lomonosov
Crater
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Unnamed
Crater
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Barnard
Crater
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Lowell
Crater
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The
images (upper left and right) show Lomonosov and an unnamed
crater 10 degrees north of it as they appeared in August
and October during the northern spring. Frost that had accumulated
during the hemisphere’s six-month winter has been shrinking
since May. In the case of the unknown crater, just 30 miles
(48 kilometers) across, portions of the frost may well persist
through the summer on its cool, shady floor -- much as it
was seen to do in Viking orbiter images acquired in the
1970s.
In the
southern hemisphere, it is now autumn on Mars, with frost
appearing as early as August in Barnard Crater (lower left).
By mid October, the frost line had moved farther north,
and the white stuff appeared in images of Lowell Crater
(lower right) as well.
In each
of the four images, north is toward the top. In the two
northern hemisphere images, the Sun illuminates the scene
from the lower left. In the southern hemisphere, the sun
does so from the upper left.
NASA’s
Global Surveyor has been orbiting Mars since September 1997.
It will be joined late next year by another NASA satellite,
the 2001 Mars Odyssey, scheduled for launch on April 7,
2001.
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