Phobos, one of two moons circling Mars, will someday create a ring around the red planet when it collapses from internal pressures that are even now changing the moon's shape.
In detailed photos taken by NASA's Mars Reconnaissance Orbiter
, long, shallow grooves on the surface of Phobos indicate structural changes that experts surmise are occurring because of gravitational tidal forces from Mars.
But the collapse and development of a ring around Mars, much like those seen on Saturn, won't take place for millions of years, NASA said
"Orbiting a mere 3,700 miles (6,000 kilometers) above the surface of Mars, Phobos is closer to its planet than any other moon in the solar system," the aeronautical agency's website said. "Mars’ gravity is drawing in Phobos, the larger of its two moons, by about 6.6 feet (2 meters) every hundred years. Scientists expect the moon to be pulled apart in 30 to 50 million years."
"We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," Terry Hurford of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said on the NASA website.
Previously, the grooves in Phobos' surface were thought to have been caused by an impact that formed the Stickney crater. However, closer study of photos determined that the grooves didn't radiate outward from the crater, but from another point nearby, NASA said.
The new theory about what caused the grooves on Phobos also brings into question conclusions about the moon's structure. It had been assumed to be "more-or-less solid all the way through," NASA said.
"The recent thinking, however, is that the interior of Phobos could be a rubble pile, barely holding together, surrounded by a layer of powdery regolith about 330 feet (100 meters) thick," the website explained.
Once the moon begins to collapse, the debris will create a ring around Mars, and then probably 100 million years after that, the ring will start to drop debris on the surface of Mars, Benjamin Black, study co-author, said in a press release.
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