Mars will someday have a ring
NASA/JPL-Caltech/University of Arizona image

Mars will someday have a ring

Two weeks ago, scientists reported that the martian moon Phobos will be torn apart as it circles inward toward the Red Planet. Now, a new study reveals what will happen as a result of that cosmic breakup: Mars will get a short-lived (in an astronomical sense) ring. Phobos, the innermost moon of Mars’s pair (seen in closeup, above), now orbits a few centimeters closer to the Red Planet each year. Once the stresses and strains imposed by gravitational interactions with the Red Planet become large enough to break apart the moon’s rocks—a threshold likely reached in the next 20 million to 40 million years, the team estimates—Phobos will be ripped apart quickly, probably in 40 days or less, the researchers report online today in Nature Geoscience. Unlike Saturn’s bright rings, which are made almost entirely of ice particles, Mars’s rocky ring will be dark and largely invisible from Earth, although the cloud of orbiting Phobos bits will at first be dense enough to cast a shadow on the Red Planet’s surface during some parts of the planet’s orbit around the sun, the researchers say. Eventually, the particles in the ring will disperse and continue their spiral into Mars’s surface, with some of the larger bits—hunks of rock up to 2 kilometers across—blasting craters as much as 4 kilometers wide. If Phobos breaks apart 40 million years from now, the ring thus formed may last only a million years, the researchers estimate. But if the ill-fated moon is ripped apart 20 million years from now, at a larger distance from Mars, the ring could last 100 million years or so. ??