[meteorite-list] HiRISE Sees Phobos in Color and Stereo

[Ron Baalke]

FROM: Lori Stiles (520-626-4402; lstiles at u.arizona.edu)

HiRISE Sees Phobos in Color and Stereo
University of Arizona
April 9, 2008

The High Resolution Imaging Science Experiment, run from The University 
of Arizona, has produced a new color stereo view of Phobos, the larger 
and inner of Mars' two tiny moons.

The HiRISE camera aboard 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," 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, HiRISE 
team member Nathan Bridges of NASA's Jet Propulsion Laboratory, in 
Pasadena, Calif., said.

"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, or 
5-and-a-half mile, Stickney is thought to have almost shattered the moon.

If Phobos' surface is analogous with 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 are among several new HiRISE images being released 
today on the HiRISE Web site at http://hirise.lpl.arizona.edu. The 
images include an anaglyph, or 3-D view of Phobos that can be viewed 
with red-blue glasses.

MRO flies at about 7,800 mph between 155 and 196 miles, or between 250 
and 316 kilometers, above the surface of Mars.

Phobos was 6,800 kilometers, or about 4,200 miles, away when the HiRISE 
camera took the first photograph. At that distance, the HiRISE camera 
was able to resolve surface features at a scale of 6.8 meters, or about 
22 feet, per pixel, and see features as small as 20 meters, or 65 feet, 
across.

Phobos was 5,800 kilometers, or about 3,600 miles, away when the HiRISE 
camera took the second picture minutes later. At that distance, the 
HiRISE camera was able to resolve features about 15 meters, or 50 feet, 
across.

Phobos, only about 13 and a half miles, or 22 kilometers, 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 7 and a half miles, or 12 
kilometers, 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.

The mission is managed by NASA's Jet Propulsion Laboratory, a division 
of the California Institute of Technology, for the NASA Science Mission 
Directorate. Lockheed Martin Space Systems, based in Denver, is the 
prime contractor and built the spacecraft. Ball Aerospace and 
Technologies Corp., of Boulder, Colo., built the HiRISE camera.


CONTACTS:
Nathan Bridges (818-393-7799; nathan.bridges at jpl.nasa.gov)
Alfred McEwen (520-621-4573; mcewen at pirl.lpl.arizona.edu)

MEDIA CONTACTS:
Lori Stiles (520-626-4402; lstiles at u.arizona.edu)
Guy Webster (818-354-6278; guy.webster at jpl.nasa.gov)

LINKS:
HiRISE - http://hirise.lpl.arizona.edu
Mars Reconnaissance Orbiter - 
http://www.nasa.gov/mission_pages/MRO/main/index.html
UA Lunar and Planetary Laboratory - http://www.lpl.arizona.edu