A Martian orbiter has spotted seasonal footprints of
spring creeping up on the red planet.
Seasonal polar caps formed from carbon dioxide have begun
vaporizing or changing directly from solid ice to gas, and have kicked off a
chain of events detected by NASA's Mars
Reconnaissance Orbiter (MRO).
"Spring on Mars is quite different from spring on
Earth because Mars has not just permanent ice caps, but also seasonal polar
caps of carbon dioxide, familiar to us on Earth as dry ice," said Candice
Hansen-Koharcheck, an MRO scientist at the NASA Jet Propulsion Laboratory in
Pasadena, Calif.
Ice caps form each Martian winter as carbon dioxide
changes directly to frost and builds dry ice layers more than three feet thick.
The arrival of warmer spring temperatures thaws the solid carbon dioxide and
thins the ice cap from both top and bottom.
The carbon dioxide gas beneath
the ice cap often flows in the same places each year, eventually creating
channels or troughs in the planet's surface. MRO has spotted many such spidery
networks of cracks that remain even after the ice caps have vanished.
Pressure from the newly thawed gas also builds up beneath
the thinning ice cap, which can lead to puffs of escaping gas and dust where
the ice cap has cracked.
"What happens on Mars, we think, is that as the
seasonal ice cap thins from the bottom, gas underneath the cap builds up
pressure," Hansen-Koharcheck said. "And where gas under the ice finds
a weak spot or a crack, it will flow out of the opening, often carrying a
little dust from the surface below."
That dust ends up swirling about in the wind before
settling in fan-like or starburst patterns, pointing
in the direction of the prevailing wind at the time. Each pattern
represents a jet of gas that was active at one time.
The Martian process differs from springtime thaws on
Earth, where frozen water melts from solid to liquid and becomes runoff. Scientists
have yet to spot flowing water on the Martian surface, though some suspect
liquids may lie beneath the surface or even inside
a volcano.
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