Mars' Moon Phobos Is Double-Doomed
Scientists have known for some time that Phobos, the larger of Mars’ two small moons, is a victim of gravity, edging closer toward its parent planet.
Scientists have known for some time that Phobos, the larger of Mars' two small moons, is a victim of gravity, edging closer toward its parent planet.
But new research shows Phobos already is starting to fall apart.
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Long shallow grooves cut into the moon's surface appear to be stress fractures, according to a study presented at the American Astronomical Society's planetary sciences meeting in Maryland this week.
Previously, scientists thought the grooves were fractures from an asteroid impact that nearly shattered the moon. The impact left a lasting impression in the form of the Stickney crater, a six-mile wide basin that is nearly half the width of Phobos itself. Later analysis showed the cracks are not stemming outward from the crater, but radiate from another point nearby.
That led to a new theory that the grooves are produced by small pieces of debris flying off Mars and smashing into Phobos, which orbits as close as just 5,800 miles above the Martian surface, closer than any other known moon circles its parent planet.
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Terry Hurford, a planetary scientist with NASA's Goddard Space Flight Center in Maryland, and colleagues have another idea. New computer models show that the grooves are aligned like stretch marks, telltale evidence of tidal forces in the ongoing gravitational tug of war between Phobos and Mars.
Phobos is losing the battle, inching closer to Mars at a rate of three- to six feet per century, Hurford told Discovery News. That gives the moon between 30 million and 50 million years before impact, but scientists doubt it'll get that far.
"We think the grooves are signs that this body is starting to break apart tidally and that these are the first evidence of the tidal deformations of Phobos," Hurford said. "Eventually, Phobos will be ripped apart before it reaches Mars' surface."
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The new computer model also predicts that the interior of Phobos is weaker than its exterior covering, which is mildly cohesive and somewhat elastic, added Arizona State University planetary scientist Erik Asphaug.
Scientists have many questions about Phobos, and its sister moon Deimos, both of which may be captured asteroids. NASA and other agencies are looking at missions to Phobos as a steppingstone to human missions to Mars.
"I think it's an exciting location," Hurford said.
New modeling indicates that the grooves on Mars’ moon Phobos could be produced by tidal forces – the mutual gravitational pull of the planet and the moon. Initially, scientists had thought the grooves were created by the massive impact that made Stickney Crater (lower right).
Ten years ago this week, NASA's Mars Reconnaissance Orbiter began a very special mission: to provide regular high-definition views of the Red Planet. Since arriving, it's spotted a lot of neat stuff -- spacecraft descending under parachutes, rovers on the surface and even dust devils. These are just a handful of some of the best pictures.
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And by the way, if you have a neat location idea for MRO to photograph,
you can submit requests yourself at the HiWish page
-- a public program for people to tell the spacecraft's
High-Resolution Imaging Science Experiment (HiRISE)
camera where to point.
NASA and the University of Arizona (which runs HiRISE) are used to precision operations. This was showcased spectacularly on Aug. 5, 2012, when the Curiosity rover landed on Mars.
The camera managed to capture the rover parachuting
safely to the surface of the Red Planet, starting a mission at Gale Crater that continues today. Previously in 2008, HiRISE also caught a view of the Phoenix lander under its parachute.
Several Mars spacecraft were on the lookout when comet C/2013 A1 Siding Spring gave the Red Planet a close shave.
This series of images from MRO on Oct. 19, 2014
was acquired from as close as 86,000 miles (138,000 kilometers) from the nucleus. That's very close in astronomical terms, the equivalent of flying a third of the way to the moon from Earth.
MORE: Mars Orbiter Beams Back Images of Comet's Tiny Nucleus
Twelve years after the Beagle lander was supposed to arrive at the Red Planet, the MRO spotted the long-lost spacecraft (which stopped communicating during landing). The image shows that the lander made it to the surface
and partially deployed its solar arrays
. It also arrived within its landing target, a circle with a radius of roughly three miles (five kilometers).
MORE: Lost Beagle Mars Lander Spotted by NASA Spacecraft
While MRO's primary target is Mars, occasionally it has caught glimpses of the planet's moons (Phobos and Deimos). In this March 23, 2008 picture,
you can see the large crater Stickney
-- as well as a bunch of troughs and crater chains that are likely unrelated to the impactor that created Stickney. The gravity of Mars is expected to tear Phobos apart in about 100 million years.
The NASA Phoenix lander was expected to last three months on the surface after landing in May 2008, but actually made it to about five. Then the spacecraft fell silent as sunlight diminished for winter. NASA kept trying to hail it until this 2010 MRO image showing damage to the lander. It is believed that
the lander's solar panels broke
after likely hundreds of pounds of carbon-dioxide ice coated the spacecraft.
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This shows a fairly common feature on Mars
, which form when winds tend to blow in one direction. It gives researchers a sense of where the dominent winds were when the features were formed. MRO is able to track seasonal changes on dunes such as these, which are near the north pole and get frosty in the winter.
Look at the brown smudge on the right side of this picture, then move your eyes left until you see a small gray dot. That's the Opportunity rover on the surface, near Victoria crater! This picture was taken by MRO in the weeks after arriving at Mars on Oct. 3, 2006. If you look carefully to the left of Opportunity and "around the corner" of the dark feature to the left and below the rover,
. The spacecraft also regularly
checks in on Mars rover Curiosity
Even though MRO is in orbit around the planet, it can spot fairly small features on Mars --
such as this solar-heat driven dust devil
! Based on the size of the shadow, it is estimated this dust devil was more than half a mile (800 meters) high, and roughly 30 yards or meters in diameter. It was spotted in the late afternoon in the north, during a time when Mars was far from the sun.
This image from Coprates Chasma is a clear example of
, which scientists believe could be evidence of flowing liquid water on Mars. While the atmosphere of the Red Planet is believed to be too thin for water to survive on the surface for long, ice melting could create temporary water flows that leave this dark evidence behind.
One benefit of MRO being at Mars at a long time is it can track change, such as this 100-foot (30-meter) crater that popped up. Roughly 200 craters happen a year when space rocks careen into the surface, but the
rays on this crater are more spectacular than most
. It was formed sometime between July 2010 and May 2012, between MRO imaging campaigns of the region.
MORE: Weirdest Mars Craters Spotted by HiRISE