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Planetary News: Mars Moons Phobos and Deimos (2008)

HiRISE Sees Phobos in Color and Stereo

 

April 9, 2008
Stickney and environs, Phobos
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Stickney and environs, Phobos
This version of a color image of Phobos taken by Mars Reconnaissance Orbiter has been stretched to exaggerate color variations within and around the nine-kilometer-diameter crater Stickney on Phobos. The floor of Stickney appears dark, while cascades of vari-colored material slide down its walls, revealing that the moon is bright on the inside. Also bright is the bluish spray of ejecta to the east(right) of Stickney. This version of the image has been rotated 180 degrees from the original release so that north is approximately up. Credit: NASA / JPL / U. Arizona

The High Resolution Imaging Science Experiment (HiRISE) aboard NASA's Mars Reconnaissance Orbiter has produced a new color stereo view of Phobos, the larger and inner of Mars' two tiny moons.

HiRISE, run from The University of Arizona (UA), 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," professor Alfred McEwen of the UA's Lunar and Planetary Laboratory, and HiRISE principal investigator, said.

Previous spacecraft, notably Mars Global Surveyor, have taken higher resolution pictures of Phobos because they flew closer to it, according to HiRISE team member Nathan Bridges of NASA's Jet Propulsion Laboratory.

"But the HiRISE images are higher quality, making the new data some of the best ever for Phobos," Bridges said. "The new images will help constrain the origin and evolution of this moon."

By combining information from the HiRISE camera's blue-green, red, and near-infrared color channels, 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 9-kilometer (5.5-mile) Stickney crater is thought to have almost shattered the moon.

More On Mars Moons Phobos and Deimos


If Phobos' surface is analogous with the surface of our own moon, "the bluer color could mean that the regolith is fresher, or hasn't been exposed to space as long as the rest of Phobos' surface has," Bridges said.

The HiRISE view also 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 analogous 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 HiRISE images of Phobos are among several new HiRISE images released today on the HiRISE website at http://hirise.lpl.arizona.edu.

Color view of Phobos from Mars Reconnaissance Orbiter
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Color view of Phobos from Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter approached to within 6,800 kilometers (4,200 miles) of Phobos to capture this enhanced-color view of the Martian moon on March 23, 2008. Credit: NASA / JPL / U. Arizona

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, or CRISM, observed both Martian moons last year. By combining HiRISE and CRISM data on Phobos, scientists can map minerals and soil types on the moons.

Find out more at The Planetary Society's blog.