NASA Spacecraft Images Mars Moon in Color and in 3D

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster@jpl.nasa.gov

Lori Stiles 520-626-4402
University of Arizona, Tucson
lstiles@u.arizona.edu

Image Advisory: 2008-055 April 9, 2008

NASA Spacecraft Images Mars Moon in Color and in 3D

PASADENA, Calif. – 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.

These images are among several new HiRISE images being released today at:

http://www.nasa.gov/mission_pages/MRO/multimedia/20080409.html . The images include an
anaglyph, or 3D view of Phobos that can be viewed with red-blue glasses.

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.

Information about the Mars Reconnaissance Orbiter spacecraft is online at

http://www.nasa.gov/mro .

The Mars Reconnaissance Orbiter mission is managed by JPL for NASA's Science Mission
Directorate, Washington. Lockheed Martin Space Systems, Denver, Colo., is the prime
contractor for the project and built the spacecraft. The University of Arizona operates the High
Resolution Imaging Science Experiment camera, which was built by Ball Aerospace &
Technologies Corp., Boulder, Colo.

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