Mars had rings in the distant past—just like Saturn currently has—and, the rings might ‘return’ in the future, says a new study published in the journal Nature Geoscience.
We know a lot about Mars: it is our closest neighbour; it is the ‘red planet’; it has water on its surface; it has no rings. But, once upon a time, millions of years ago, it did have its own set of rings. These rings might even ‘return’ someday, millions of years from now. This is the conclusion reached by a team of scientists from Purdue University who put together a model suggesting that debris generated from a collision with Mars—an event that might have occurred 4.3 billion years ago—turned into a planetary ring. Another theory attributes Mars’ North Polar Basin (also known as Borealis Basin) to such a collision.
Author Andrew Hesselbrock explains that the Borealis Basin extends over 40% of the planet, and that it was formed at an impact from an asteroid or other heavenly body which resulted in debris from Mars flying into space. This collision would have been powerful enough to eject sufficient materials to create a ring, says Hesselbrock.
If this is true, where is the ring now? The model put together by Hesselbrock and his colleague, David Minton, suggests that this ring, together with other debris, gradually shifted away from Mars, and eventually collected together to form a moon. So, the ring turned into a moon at some point in time. Now, what happened to this moon? It would have been attracted to Mars through the force of gravity, reaching the Roche limit, when the tidal forces of the planet would have torn it apart, resulting in the creation of more rings.
How will Mars have rings in the future? The model suggests that its existing moon, named Phobos, which is already moving closer to Mars, will have reached the Roche limit in around 70 million years—Phobos will, then, break apart, forming a new set of rings.
Minton and Hesselbrock are of the opinion that the appearance and disappearance of rings around Mars have occurred several times before: this cycle—a moon breaking apart into rings, and reforming from the latter, which would then gather into another moon—would have repeated from 3 to 7 times in the distance past.
The model also suggests that each subsequent moon decreases in size: 5 times smaller than the previous one.
The existence of Phobos is also mentioned in other theories. For instance, one of these says that it was created 4.3 billion years ago when the North Polar Basin was formed on impact. However, Minto argues that Phobos could not have lasted for such a long time: it must be younger.
The pair of researchers now intend to focus their efforts on either the first set of rings of Mars or on the debris falling onto Mars when its moons were destroyed.