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Did Mars once have rings? Scientists say it’s possible

Published Jun 3rd, 2020 7:04PM EDT
mars rings
Image: NASA Goddard

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  • Mars may have once had rings, and researchers say the evidence may still be orbiting the planet today.
  • Phobos, the tiny Martian moon, may have once been much larger, slowly getting closer to Mars until it was torn to shreds and formed a ring of dust and debris.
  • That ring may have then coalesced into a moon once again, and this pattern could have repeated several times in the history of our solar system.

We think of Mars today as a big, mostly barren orange rock. It’s like Earth if Earth had its atmosphere stripped away and had to endure billions of years of erosion as it lost its water to space. Long ago, Mars looked a lot different. It was wet, and perhaps even supported life in some form. According to new research presented at a recent meeting of the American Astronomical Society, it might have also sported rings.

But how could we possibly know whether or not Mars had rings billions of years ago? Surely the evidence of the rings is long gone, right? Maybe not. The researchers behind the study suggest that the strange Martian moons Deimos and Phobos may explain a cycle of ring creation and destruction around Mars.

First, the scientists began with what they know based on data and observations of Phobos. Phobos is gradually falling closer and closer to the Martian surface. It’s happening very slowly, but eventually, it will get too close to remain intact and the gravitational pull of the planet and the speed of the moon in orbit will cause it to be torn to pieces.

Some of those pieces may fall to the surface, but much of the debris could continue to orbit Mars, with chunks crashing into each other, generating dust, and spreading out into a true planetary ring. Even more interesting, it’s possible that the ring could eventually reform into a moon, and the scientists say that it’s possible this has already happened to Phobos in the past, cycling between moon and ring at different stages of its life and getting smaller every time.

Okay, so Phobos might eventually turn into a ring, but how does that hint at past rings? Well, Deimos, another Martian moon, has a very odd orbit. It doesn’t circle the planet on the same plane as Phobos and instead has an inclined orbit that scientists have never fully explained. The researchers suggest that Deimos’ unique orbital characteristics are actually the result of some other large body interacting with it.

That object may have been an entirely different early moon or perhaps an earlier version of Phobos. A much larger version of the now-tiny moon could have easily affected the orbit of Deimos and pushed it into the strange orbit it now enjoys.