Phobos Ring Mars May Get Ring

© Uni. of Arizona/REX Shutterstock

Mars' new bling could one day rival Saturn's ring - Someday Mars could flash its very own ring – a trinket made from bits of a Martian moon now being torn apart by Mars itself.

Scientists have long known that Phobos, the bigger of Mars’ two petite moonlets, is spiraling dangerously close to its home planet. But Phobos’ ultimate destiny had not been clear. Now researchers report that much of Phobos will be shredded into pieces like a tree in a wood chipper. The remnants will form a ring like Saturn’s, making Mars the only planet in the inner solar system to sport a ring.

If Phobos shatters all at once, “you’d expect the ring to unfurl … very quickly, over the course of days to weeks,” said study author and planetary scientist Benjamin Black, who will soon join City University of New York. Someone standing on the surface of Mars “might see a bright arc in the sky.”

It would be a spectacular end after a violent demise. Tiny Phobos, which is less than 1% the size of Earth’s moon, is being drawn to its doom by the lopsided gravitational pull of Mars. Phobos’ so-called “stretch marks” – long grooves in the surface – attest to the strain on the tiny body. As it draws near Mars, it faces two unappealing outcomes: collision or disintegration.

To predict Phobos’ end, Black and his colleague Tushar Mittal, a graduate student at the University of California, Berkeley, examined its structure and found the moon is only slightly denser than gravel or wet sand. Rather than holding together until it slams into the Red Planet, much of Phobos will crumble as Mars looms in view 20 to 70 million years from now.

The shards will remain in orbit, encircling Mars as a ring that may be slightly less shiny than Saturn’s but still dramatic. Any big leftover chunks of Phobos will strike Mars. Depending on where any observers on Mars were standing, they might see a bright arc or a shadow, Black said.

Other scientists also think Phobos is likely to bestow a ring on Mars. But so much about Phobos is a mystery that it’s difficult to predict its future with any certainty, said astrophysicist Zoe Leinhardt of Britain’s University of Bristol.  

“I would say there would be some ring,” she said, “but all of that goes with a ‘based on the evidence we have at the moment.’ ” Black agreed, noting that many traits of Phobos that will determine whether it smacks into Mars or falls apart are a “big unknown.”

Sending a spacecraft to Phobos would help clarify how it will end its days. In the last few years, three research teams have proposed missions to Phobos. NASA hasn’t yet funded one, so Mars will have to wait to be certain there’s some flashy new bling in its future.