Peering
beneath the ice at the north pole of Mars has now revealed the red planet may
be surprisingly colder than was thought.
Any liquid
water that might exist on Mars therefore might be hidden deeper
than once suspected, closer to that world's warm heart, researchers
suggested.
An
international team of scientists used the Mars Reconnaissance Orbiter to probe
the north pole of the red planet with radar. The ice cap there goes about
1.2 miles deep (2 km) and is roughly the size of Pakistan at 310,000 square miles large (800,000 square km).
These scans
revealed the polar cap has up to four layers of ice rich in sand and dust, each
separated by clearer sheets of nearly pure ice. Each dirty and clean layer is
some 1,000 feet thick (300 meters).
These dirty
and clean layers were created by ages of intense dust storms followed by icy
eras. This five-million-year-long cycle was likely driven by wobbles in
Mars' tilt and fluctuations in the shape of its orbit around the sun. The
more sunlight the red planet saw because of these changes, the more the polar
icecaps retreated and the more dust storms Mars saw.
"All
this layering is key evidence for theoretical models that predict that changes
in Mars' climate are coupled with orbital changes," said researcher Roger Phillips, a geophysicist at
Southwest Research Institute in Boulder.
Unexpectedly,
the radar scans also revealed the massive weight of the ice cap does not deform
any underlying sediment. This implies the crust beneath the cap is strong —
more than 180 miles thick (300 km).
To have
such a thick crust, "Mars might be colder than we thought," Phillips
told SPACE.com. As a result, any liquid water that might be underground has to
be buried even deeper than once speculated. "If one thought that liquid
water was 5 kilometers deep (3 miles), it's now at least 30 percent deeper than
that," he said.
Philips and
his colleagues detailed their findings online May 15 in the journal Science.
As to why
Mars might be so cold, "perhaps it was robbed of its fair share of
heat-producing elements, such as uranium and thorium, when it was first
born," Phillips said. Or perhaps the way heat flows on Mars is quite
variable, with the crust being colder and thicker at the poles and hotter
elsewhere — "like Mars' volcanic provinces of Tharsis and Elysium."
The
upcoming Phoenix
Lander mission, which will explore
the water ice just underneath the surface soil of the Martian arctic
plains, might help shed light on the layering at Mars' north pole. To solve the
mystery of the heat of Mars, heat flow probes are likely needed all over that
planet, as is suggested by the Mars Network Mission under proposal, Phillips
said.
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