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NASA Spacecraft Reveal Largest Crater in Solar System

Written by thomas · Filed Under Aeronautics News 

June 25, 2008

thomas

PASADENA, Calif., June 25 /PRNewswire-USNewswire/ — New analysis of
Mars’ terrain using NASA spacecraft observations reveals what appears to be
by far the largest impact crater ever found in the solar system.

NASA’s Mars Reconnaissance Orbiter and Mars Global Surveyor have
provided detailed information about the elevations and gravity of the Red
Planet’s northern and southern hemispheres. A new study using this
information may solve one of the biggest remaining mysteries in the solar
system: why does Mars have two strikingly different kinds of terrain in its
northern and southern hemispheres? The huge crater is creating intense
scientific interest.

The mystery of the two-faced nature of Mars has perplexed scientists
since the first comprehensive images of the surface were beamed home by
NASA spacecraft in the 1970s. The main hypotheses have been an ancient
impact or some internal process related to the planet’s molten subsurface
layers. The impact idea, proposed in 1984, fell into disfavor because the
basin’s shape didn’t seem to fit the expected round shape for a crater.

The newer data is convincing some experts who doubted the impact
scenario.

“We haven’t proved the giant-impact hypothesis, but I think we’ve
shifted the tide,” said Jeffrey Andrews-Hanna, a postdoctoral researcher at
the Massachusetts Institute of Technology in Cambridge.

Andrews-Hanna and co-authors Maria Zuber of MIT and Bruce Banerdt of
NASA’s Jet Propulsion Laboratory in Pasadena, Calif., report the new
findings in the journal Nature this week.

A giant northern basin that covers about 40 percent of Mars’ surface,
sometimes called the Borealis basin, is the remains of a colossal impact
early in the solar system’s formation, the new analysis suggests. At 5,300
miles across, it is about four times wider than the next-biggest impact
basin known, the Hellas basin on southern Mars. An accompanying report
calculates that the impacting object that produced the Borealis basin must
have been about 1,200 miles across. That’s larger than Pluto.

“This is an impressive result that has implications not only for the
evolution of early Mars, but also for early Earth’s formation,” said
Michael Meyer, the Mars chief scientist at NASA Headquarters in Washington.

This northern-hemisphere basin on Mars is one of the smoothest surfaces
found in the solar system. The southern hemisphere is high, rough, heavily
cratered terrain, which ranges from 2.5 to 5 miles higher in elevation than
the basin floor.

Other giant impact basins have been discovered that are elliptical
rather than circular. But it took a complex analysis of the Martian surface
from NASA’s two Mars orbiters to reveal the clear elliptical shape of
Borealis basin, which is consistent with being an impact crater.

One complicating factor in revealing the elliptical shape of the basin
was that after the time of the impact, which must have been at least 3.9
billion years ago, giant volcanoes formed along one part of the basin rim
and created a huge region of high, rough terrain that obscures the basin’s
outlines. It took a combination of gravity data, which tend to reveal
underlying structure, with data on current surface elevations to
reconstruct a map of Mars elevations as they existed before the volcanoes
erupted.

“In addition to the elliptical boundary of the basin, there are signs
of a possible second, outer ring – a typical characteristic of large impact
basins,” Banerdt said.

JPL manages the Mars Reconnaissance Orbiter for NASA’s Science Mission
Directorate, Washington. For more information about the mission, visit:

http://www.nasa.gov/mro

SOURCE NASA

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