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NASA
Spacecraft Images Mars Moon in Color and in 3D
Wednesday, April 9, 2008
Credit:
NASA/JPL-Caltech/University of Arizona
Credit: NASA/JPL
Caltech/
University of
Arizona
A new stereo view of
Phobos, the larger and inner of Mars' two tiny moons, has been
captured by a NASA spacecraft orbiting Mars.
The High
Resolution Imaging Science Experiment (HiRISE) on NASA's Mars
Reconnaissance Orbiter took two images of Phobos 10 minutes apart
on March 23. Scientists combined the images for a stereo
view.
"Phobos is of great interest because it may be
rich in water ice and carbon-rich materials," said Alfred
McEwen, HiRISE principal investigator at the Lunar and Planetary
Laboratory at the University of Arizona, Tucson.
Previous
spacecraft, notably Mars Global Surveyor, have taken
higher-resolution pictures of Phobos because they flew closer to
the moon, said Nathan Bridges, HiRISE team member at NASA's Jet
Propulsion Laboratory in Pasadena, Calif.
"But the
HiRISE images are higher quality, making the new data some of the
best ever for Phobos," said Bridges. "The new images
will help constrain the origin and evolution of this moon."
By
combining information from the camera's blue-green, red and
near-infrared color filters, scientists confirmed that material
around the rim of Phobos' largest surface feature, Stickney
crater, appears bluer than the rest of Phobos. The impact that
excavated the 9-kilometer (about 5.5 mile) in diameter Stickney
crater is thought to have almost shattered the moon.
"Based
on analogy with material on our own moon, the bluer color could
mean that the material is fresher, or hasn't been exposed to
space as long as the rest of Phobos' surface has," Bridges
said.
The new view shows landslides along the walls of
Stickney and other large craters: Phobos' striking surface
grooves and crater chains; and craters hidden on the moon's dark
side illuminated by "Marsshine."
"Marsshine"
is sunlight reflected by Mars onto the moon. The phenomenon is
similar to "Earthshine," where Earth reflects sunlight
that illuminates the dark side of our moon. Like Earth's moon,
Mars' moons Phobos and Deimos are "tidally locked" on
their planet, that is, they always present the same side to the
planet they orbit.
The Mars Reconnaissance Orbiter flies
at about 4,800 kilometers per hour (7,800 mph) between 250 to 316
kilometers (155 and 196 miles) above the surface of Mars.
Phobos
was 6,800 kilometers (4,200 miles) away when the HiRISE camera
took the first photograph. At that distance, the camera was able
to resolve the surface at a scale of 6.8 meters (about 22 feet)
per pixel, and see features as small as 20 meters (65 feet)
across.
Phobos was 5,800 kilometers (3,600 miles) away
when the HiRISE camera took the second picture minutes later. At
that distance, the camera was able to resolve features about 15
meters (50 feet) across.
Phobos, only about 22 kilometers
(13.5 miles) in diameter, has less than one-thousandth the
gravity of Earth. That's not enough gravity to pull the moon into
a sphere, so it's oblong. Mars' second moon, Deimos, is even
smaller, at about 12 kilometers (7.5 miles) across. The very
dark, diminutive moons may be captured asteroids from the outer,
carbon-rich, Mars-Jupiter asteroid belt.
The Mars
Reconnaissance Orbiter's Compact Reconnaissance Imaging
Spectrometer for Mars, observed both Martian moons last year. By
combining the data with HiRISE data on Phobos, scientists can map
minerals and soil types on the moons.
Source:
NASA / JPL
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