The solar system may gain another ringed planet like Saturn, as Mars may one day sport a ring created by the disintegration of one of its moons, a new study suggests.
A previously published study detailed how the small moon Phobos is in the process of being slowly stretched and pulled apart by the red planet's gravity. Now, a new study suggests that cosmic breakup could create a ring around Mars.
The solar system currently has four ringed planets; Saturn, with by far the largest and brightest ring system, and the other gas giant planets Jupiter, Uranus and Neptune, all of which possess much fainter rings.
Writing in the journal Nature Geoscience, researchers say their calculations suggest Phobos may disintegrate and form a ring system around Mars in some 20 million to 40 million years.
Phobos is moving closer to Mars every year as the tidal forces of the red planet's gravity pull on it, about 6.5 feet each century, and some scientists say that will end with a collision of the moon and its parent planet.
However, the new study suggests Phobos may simply disintegrate long before such a collision takes place.
"The main factor affecting whether Phobos will crash into Mars or break apart is its strength," says Tushar Mittal, one of the study's authors and a graduate student at the University of California, Berkeley. "If Phobos is too weak to withstand increasing tidal stresses, then we expect it to break apart."
That breakup could happen quickly, in perhaps weeks or even just day, says UC Berkeley planetary scientist and study co-author Benjamin Black.
"If you were standing on the surface of Mars, you could grab a lawn chair and watch Phobos shearing out and spreading into a big circle," he says.
Black says he and Mittal calculate the resulting ring could last 1 million to 100 million years before falling to the surface of Mars.
Larger ring particles would fall first, but smaller particles would remain in orbit around the red planet longer, he says.
Unlike Saturn's rings, visible from Earth because they consist almost exclusively of highly reflective ice particles, a Martian ring created by the breakup of Phobos would be dark and for the most part invisible from the Earth.
Mars has two moons, Phobos and Deimos, named for the children of Ares, a Greek god the equivalent of the Roman god of war Mars.
Phobos is the closer of the two; the tiny moon 13 miles in diameter orbits just 3,700 miles above Mars, and is getting closer all the time.
"Phobos is unique in that it is currently one of only a couple of inwardly evolving moons in our solar system that we know about," says Mittal. "However, since inwardly evolving moons inadvertently self-destruct, it is possible that more inwardly migrating moons may have existed in the past."