SAN
FRANCISCO—NASA scientists have discovered what might form some of the weirdest
landscapes on Mars, winding channels carved into the Martian surface that
scientists have dubbed "spiders," "lace" and "lizard skin."
The unusual
landscape features form in an area of Mars' south pole called cryptic terrain
because it once defied explanation.
But new
observations from NASA's Mars Reconnaissance Orbiter, presented here today at a
meeting of the American Geophysical Union, bolster theories that the intricate
patterns may be sculpted by springtime outbursts
of carbon dioxide gas from underneath the frozen-carbon dioxide polar ice
cap.
Bottom-up
Mars, like
Earth, has seasons that shift as the planet orbits the sun. During the southern
hemisphere winter, some of the carbon dioxide in the planet's atmosphere
freezes to form a translucent
ice cap made of the gas.
Come
spring, the sun's rays penetrate this layer of ice and begin to warm the red-rock
surface underneath.
"The sun
passes through the ice and warms up the surface because the surface is dark and
absorbs the sunlight," explained mission scientists Candice Hansen of NASA's
Jet Propulsion Laboratory in Pasadena, Calif.
The warm
surface then heats the ice layer from the bottom up, causing carbon dioxide gas
to sublimate (like dry ice fumes used to imitate fog at a haunted house) from
it and gather underneath the ice.
As the gas
accumulates and its pressure increases, it seeks out weak spots in the ice and
bursts forth, spewing carbon dioxide gas back into the Martian atmosphere. The
gas carries some of the dust
from the surface along with it, which then settles into "fans" on top of
the ice.
"It's a
process unlike anything we have on Earth," Hansen said.
Intricate
patterns
As the
surface material is carried out by the rushing gas, channels are carved into
the surface that form intricate patterns. Some, which scientists have dubbed
"spiders," have spindly channels that radiate outward from a center point.
Hansen describes other patterns as appearing like lace or scaly lizard skin.
Just what
causes these different shapes is a mystery. It could be different features of
the underlying landscape or differences in the way the gas moves under the ice,
but one thing is for sure Hansen said, "there's something that causes the
different morphologies."
Fields of
fans of surface material are scattered on top of the ice that overlies the
channel features, increasing as the spring wears on and the sun beats down more
intensely. Eventually, as summer approaches, all the ice evaporates away,
leaving only the intricate scars on the Martian surface.
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