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Hi-Def Anxiety: Colorful Photo of Fearless Phobos
4/22/2008
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Small, misshapen Phobos has not had an easy time of it. The larger of Mars' two satellites, the moon takes its name from the Greek personification of fear.
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Small, misshapen Phobos has not had an easy time of it. The larger of Mars' two satellites, the moon takes its name from the Greek personification of fear. Like most dusty bodies in our solar system, it does bear the scars of regular peltings by smaller objects whose passage through our solar system came to an abrupt halt on the Phobian surface. But at least one of these objects was not small at all and nearly smashed the little moon to bits. The name seems apt.
The collision created the yawning Stickney Crater, which takes up nearly half the area visible on Phobos' illuminated side, above. Measuring 9-kilometers (5.5 miles) wide, the dent was named by Phobos' discoverer after his wife (an interesting honor considering the crater's place in the moon's history). NASA's Mars Reconnaissance Orbiter has just sent back new views and information on the crater and other features on Phobos, captured on March 23, 2008 by the orbiter's HiRISE (High Resolution Imaging Science Experiment) camera.
Blue-green, red, and near-infrared channels on HiRise set Stickney Crater into deep, colorful relief and highlighted features not clearly visible on previous higher-resolution, black-and-white images of Phobos. A splash pattern of materials on Stickney's rim, that may or may not be the result of the impact itself, appear bluish in the new images. Freshly exposed areas on our own moon are similar, suggesting that those on Phobos have not been bared to open space as long as their surroundings. The images also clearly show deep trenches and chains of small craters that seem to radiate from Stickney in this image. Earlier pictures indicate that these weren't gouged out when the big crater was, however. Instead, it is likely that poor Phobos was splattered with debris from asteroid impacts on Mars.
Once possibly a free-wheeling asteroid itself, the small moon may have been hauled in for a more circumscribed life by Mars' gravitational pull. Phobos measures only 22 kilometers (13.5 miles) in diameter at its widest. To put this into perspective, 2008 Boston Marathon winner Robert Cheruiyot just ran almost twice that distance in 2 hours, 7 minutes, and 46 seconds. That's a tiny moon. With so little mass, Phobos has only one-thousandth of Earth's gravity. That is enough to cause landslides—the light streaks visible along Stickney's edge show where its rim has collapsed—but Lilliputian Phobos never could scrape together enough gravity to pull itself into the smoothed, spherical shape of larger bodies. Then again, who needs lots of gravity and a fancy atmosphere? Phobos has survived, which is plenty for one whose universe has dealt it such a battering.
—Jessa Forte Netting
Links
HiRISE
More Phobos images in color, black & white, and 3D
Mars Reconnaissance Orbiter spacecraft
For Further Study
Mars,
Satellite (astronomy),
Asteroid,
Space probe,
Space flight [2007 YB and Research update],
Q&A: Why are celestial bodies spherical?
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