By Deborah Zabarenko
WASHINGTON (Reuters) - Mars whipped up a swirling pink storm
at its north pole, dozens of dust devils in the south and vast
shifting sand dunes that seem sprinkled with frost, new data
from NASA showed Tuesday.
The latest images from the Mars Global Surveyor space probe
show the Red Planet's weather to be highly dynamic, with forms
similar to those on earth, with the notable exception of rain.
There might be snow on Mars, though, as indicated by the
light dusting of frost -- made up both of water ice and carbon
dioxide -- on an area of sand dunes.
``We don't know whether (the frost) forms on the ground, and
grows up out of the ground, or falls out of the atmosphere as
snow,'' said Michael Malin, the main scientist for the
spacecraft's camera.
The frost clings to the shifting dunes, disappearing as the
Martian spring approaches and reappearing in winter, Malin and
others said at a briefing at NASA headquarters. Mars also has
polar ice caps that wax and wane with the seasons.
The dunes interest astronomers because of their similarity
in size to those on earth. One scientist, Jim Zimbelman, said
the dunes were exactly the same scale as those he has studied in
the Mojave Desert in the southwestern United States.
Earlier missions to Mars have pictured dunes several times
the size of those on earth.
The dunes, shown in images taken this month, are dark in
color, which probably means the light dust that settles over
most of Mars does not accumulate on them -- another sign that
they are in constant motion.
But not all the dunes are alike, the scientists found.
One picture showed what looks very much like pine trees
poking through a blanket of snow, though at a temperature of
about minus 150 degrees Celsius, that is impossible.
The scientists believe that these dark spots are the signs
of seasonal warming on the dunes as they are exposed to spring
sunlight. Ice does not melt into liquid water on Mars, but
sublimes, that is, it changes directly from a solid to a gas,
the way ``dry ice'' does on earth.
These patches of sublimation give different parts of the
Martian dunes different appearances, with some looking striped,
others like freckles and still others showing the ripples of
wind erosion.
The dust devils of Mars are much bigger than those on earth,
though they form in about the same way, as spinning columns of
air that lift dust from the planet's surface.
Earthly dust devils may be some two yards (meters) high,
while those on Mars can grow to five miles (eight km) in height.
They can drag tons of dust with them as they move, but have much
less power than tornadoes do on earth, and are formed in a
different way.
In addition to the scientific findings, the new images have
a practical purpose for the National Aeronautics and Space
Administration: they will help earthly controllers decide where
to land the Mars Polar Lander craft, set to arrive at the Red
Planet on December 3.
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