Mars is
unlikely to sport beachfront property anytime soon, but the planet has enough
water ice at its south pole to blanket the entire planet in more than 30 feet
of water if everything thawed out.
With a
radar technique, astronomers have penetrated for the first time about 2.5 miles
(nearly four kilometers) beneath the south pole's frozen surface. The data
showed that nearly pure water
ice lies beneath.
Discovered
in the early 1970s, layered deposits of ice
and dust cap the North and South Poles of Mars.
Until now, the deposits have been difficult to study closely with existing
telescopes and satellites. The current advance comes from a probe of the
deposits using an instrument aboard the Mars
Express orbiter.
"This is
the first time that a ground-penetrating system has ever been used on Mars,"
said the new radar study's lead author, Jeffrey Plaut of NASA's Jet Propulsion
Laboratory. "All the other instruments used to study the surface of Mars
in the past really have only been sensitive to what occurs at the very surface."
(NASA's Mars
Odyssey spacecraft also carries instruments designed, among other things,
to probe beneath icy polar surfaces.)
Deep
probe
Plaut and
his colleagues probed the deposits with radar echo sounding, typically used on Earth to study the interiors of glaciers.
The instrument, called the Mars Advanced Radar for Subsurface and Ionospheric
Sounding, or MARSIS,
beams radio waves which penetrate the planet's surface and bounce off features
having different electrical properties.
The
reflected beams revealed that 90 percent or more of the frozen polar material
is pure water ice, sprinkled with dust particles. The scientists calculated
that the water would form a 36-foot-deep ocean
of sorts if spread over the Martian globe.
"It's the
best evidence that's been obtained to date for that thickness," said Ken Herkenhoff, a planetary
geologist at the U.S. Geological Survey in Flagstaff, Ariz., who studies the Martian polar regions.
He was not involved in the current study.
Scientists
have long known that Mars'
north polar cap is a massive storehouse of water ice, and the current
research team says they will use their radar technique to refine past estimates
of its thickness and make-up.
Missing
water
"These
polar ice deposits are by far the largest reservoir of water or water ice that
we know of on Mars," Plaut said.
That's a
lot of water, but not enough to account for the flowing
streams thought to meander
along Mars' surface in the past.
"There's
evidence that about 10 times or maybe even 100 times that much water has flowed
across the surface of Mars to carve the various channels, the outflow valleys
and other features we see in the images and topography data," Plaut told SPACE.com.
So where's
the rest of the water? One idea is that a subterranean plumbing system once
ferried loads of water beneath the Martian surface. Plaut said his team also will
search for underground pools with the radar technique.
Martian
beach
A Martian
water-world is unlikely in the near future, but astronomers have solid evidence
that billions of years ago water flowed over the Martian
surface. And recently, evidence has pointed to a warming trend as Mars
emerges from an "ice age."
Scientists
think variations in Mars' orbit and tilt drive the planet's climate over time, though a few
astronomers have speculated about how the Sun's
activity could be partly to blame for warming on several planets.
In addition
to warming from the atmosphere, ice-thawing heat could come from the core of Mars, analogous to the plumes of heat
that cause volcanic eruptions
on Earth. But evidence from the new radar study suggests the Martian crust is
icy cold and rigid.
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