NASA's Mars Global Surveyor (MGS)
spacecraft has spotted new gullies and a fresh crater - in astronomical terms -
etched into the red planet's surface, mission scientists said Tuesday.
Now in its eighth year in orbit
around Mars, the MGS spacecraft found the new gullies cutting through a sand
dune, as well as numerous other signs that the planet is far from a static,
unchanging world.
"[The gullies] are probably not the
result of water action on the sand dune," said Michael Malin,
principal investigator for the Mars Orbiter Camera aboard MGS, during
teleconference with reporters. "What we think is going on here is that carbon
dioxide snow has been incorporated into the sand dune."
As the snow melts and evaporates
into gas, it allows the sand around it to fluidize and
run down the dune slope, Malin added.
The gullies are unique in that
they're carved in sand, and not in the rock faces of crater walls, researchers
said. [An animation of the gullies spied by MGS is available here.]
Meanwhile, researchers poring
through MGS images by hand found a fresh crater
that apparently formed in the 1980s.
The crater, a 65-foot (20-meter) pit
carved into the southern rim of the Martian volcano Ulysses Patera,
did not appear in photographs taken by NASA's Viking orbiter in 1976. But MGS'
camera found the crater, ringed by a dark ejecta
blanket and radial lines, in 1999. By 2005, the ejecta
blanket was nearly faded, but the crater remained.
Based on the amount of ejecta fading, researchers estimated the crater formed
between 1980 and 1985, and believe it is the remains of an impact by a small
hunk of rock a few feet in diameter.
"Actually, we have five or six of
these types of craters," Malin said, adding that
unlike the Ulysses crater, most of the others were not in areas also studied by
Viking. "The number [of young craters] we've seen is much less than the number
we'd predicted."
Before MGS arrived at Mars in 1997,
researchers expected to find much more evidence of impact craters, given the
planet's location near the asteroid belt, researchers said. But MGS has only
photographed about four percent of the Martian surface, and there may be many
more young craters waiting to be found, they added.
"I suspect that the reason why the cratering rate looks different is that the impact rate
comes in clusters, and not a constant, uniform bombardment," Malin said.
Rockfalls and ice caps
Mars scientists also revealed MGS
images of a recent rockfall, in which many boulders
broke free and rolled down a crater wall sometime between November 2003 and
December 2004.
Researchers are unsure whether the rockfall was caused by strong winds, an
nearby impact event or seismic activity.
"These images describe a dynamic
surface of the planet Mars," said Jack Mustard, an associate professor of
geological sciences at Brown University, during the telecon.
"They catch Martian geology in action."
If the rockfall
was caused by seismic activity, such as a marsquake, it could support views that Martian
tectonics and volcanism are still active at the planet, Mustard added.
The spacecraft also observed a
gradual evaporation of carbon dioxide ice in one of Mars' polar caps, pointing
to a slowly changing Mars climate.
"They way these polar pits are
retreating is absolutely astounding," Mustard said.
But like the rockfalls,
researchers were unable to account for the gradual climate change.
"Why is Mars warmer today that it
was in the past, we really have no way of knowing why," Malin
said.
An orbiter's long life
NASA's MGS mission is in its third extended
mission phase, and the added years have been crucial to its ability to
explore Mars, researchers said.
"Some of the things [observed]
changed in few weeks or months, and others have changed over years," Malin said. "Most of the discoveries that we've made came
during the extended mission."
The spacecraft has returned more
than 250,000 images of Mars and a wealth of other data from its onboard
instruments, NASA officials have said.
In addition to its Mars-watching
role, MGS has spied
two of its fellow red planet orbiters - NASA's Mars Odyssey and the European
Space Agency's Mars Express spacecraft - during its mission.
Michael Meyer, NASA's Mars
Exploration Program chief scientist, said that overall, MGS remains in good
health and still has years of red planet exploration ahead of it.
NASA has budgeted about $9.5 million
for the MGS mission this year, and the spacecraft has enough propellant to last
well into the next decade, Meyer said.
"I think we have much more science
to be done by this spacecraft itself, and it will serve an important function
as a communications asset [for future missions]," Meyer said.
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