New Evidence Suggests That Mars Indeed Had a Ring

Mars - glorious, dusty, complex Mars - may once have been even more dazzling. New research provides even more evidence that a rubbly ring once circled the Red Planet. The new clue lies in Deimos, the smaller of the two Martian moons. It's orbiting Mars at a slight tilt with respect to the planet's equator - and this could very well be the result of the gravitational shenanigans caused by a planetary ring. Ring systems aren't actually all that uncommon. When you think about ring systems, your mind immediately leaps to Saturn, no doubt - but half the planets in the Solar System have rings, Saturn, Uranus, Neptune, and Jupiter.

In 2017, a pair of researchers theorised that Mars, too, once had a ring. They conducted simulations of the larger of the two Martian moons, Phobos, and found that it could have formed after an asteroid slammed into Mars, sending debris flying into space, forming a ring that then clumped together into an earlier form of Phobos that was much more massive than it is today.

Now this new research has added Deimos into the mix - and the findings are in total agreement with the previous model.

"The fact that Deimos's orbit is not exactly in plane with Mars's equator was considered unimportant, and nobody cared to try to explain it," said astronomer Matija Ćuk of the SETI Institute.

"But once we had a big new idea and we looked at it with new eyes, Deimos's orbital tilt revealed its big secret."

Deimos' orbital tilt isn't huge - just 1.8 degrees off Mars' equator. Aside from that, its orbit is pretty normal - it swings around Mars every 30 hours or so, with extremely low eccentricity - so you can see why no one thought anything screwy was going on. But there is something screwy going on with Phobos. It's much closer...