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Mars once had rings of its own, new research suggests

Saturn is the planet in our solar system that’s famous for its beautiful rings, but it may once have had competition from our neighbor, Mars.

New research from the SETI Institute and Purdue University suggests that millions of years ago, Mars may have had rings of its own.

The new research provides evidence in support of the ring hypothesis by looking at the unusual orbits of Mars’ moons. Both of its two moons, Phobos and Deimos, orbit in a similar plane to its equator, but Deimos orbits at a slight angle, tilted by two degrees.

“The fact that Deimos’s orbit is not exactly in-plane with Mars’ equator was considered unimportant, and nobody cared to try to explain it,” lead author
Matija Ćuk, a research scientist at the SETI Institute, said in a statement. “But once we had a big, new idea and we looked at it with new eyes, Deimos’ orbital tilt revealed its big secret.”

Rendering showing a planetary ring system over Mars.
A rendering shows a planetary ring system over Mars, demonstrating either the formation or destruction of its moons, Phobos and Deimos. Kevin Gill

Scientists already knew that Mars could develop a ring in the far future, as its fragile moon Phobos will be pulled toward the planet over millions of years and ripped apart by its tidal forces to form a ring of rocky particles that will encircle it.

This is estimated to happen in approximately 70 million years’ time. It may even be possible that this is part of an enormous cycle in which the rocky matter that constitutes the moon is pulled apart and pushed back together, with Mars oscillating between having rings and moons.

Ćuk and his colleagues argue that the tilt of Deimos must have arisen from the presence of a second massive moon in addition to rings. This second massive moon was the “grandparent” of Phobos. It was 20 times Phobos’ mass and existed more than 3 billion years ago. Since then, this body has undergone two more cycles of destruction and reformation as rings and moon.

This research remains theoretical, but there may be experimental evidence available within a few years if the Japanese Space Agency sends its planned spacecraft to Phobos. Samples from Phobos could reveal more about the origin of the moons and the history of Mars.

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