Mars is to lose a moon but gain a distinctive ring

The planet Mars is going to lose a moon but gain a distinctive ring when the larger of its two moons Phobos begins to disintegrate in orbit.

Phobos is already beginning to show cracks and weak points on its surface, caused by Mars’ gravitational pull.

And Phobos is also drifting slowly closer to its host planet, say researchers from the University of California, Berkeley.

We won’t be around to see the fireworks when Phobos gets shredded given it won’t happen for 10 to 20 million years or more but the moon is already doomed and its fate is sealed.

The research question to be answered was would there be a slow but colossal collision or would the moon get torn apart while still in orbit to form an attractive ring.

Postdoctoral research fellow Benjamin Black and graduate student Tushar Mittal created models to study this and conclude Phobos is going to put a ring on it, publishing their view online in Nature Geoscience.

Our moon is fairly solid throughout while Phobos is a much looser assemblage.

And our moon is actually moving away from Earth by a few centimetres a year, while Phobos is slowly moving closer to Mars by a few centimetres a year, the researchers say.

The pull of gravity is already leaving its mark and things will only get worse over time.

They believe it will break up in orbit, although larger chunks will still rain down on Mars, leaving plenty of egg-shaped impact craters. This will leave loads of rubble in orbit to spread out and form a ring.

If the big breakup happens well up at over 680km above the surface then the ring will be “really narrow”.

Over time, however, the ring would spread out and get wider, the two researchers say on the basis of their models.

There would be a steady stream of material raining down on the plant for millions of years afterwards as gravity reeled in the material.

It is unlikely to be a showy ring, unfortunately. Saturn’s rings are highly visible because of ice crystals distributed through them.

The Martian ring would be dry dark rubble so wouldn’t provide a good show from Earth, the researchers say.

Things will be different if we have humans on Mars 20 million years from now.

“Standing on the surface of Mars a few tens of millions of years from now, it would be pretty spectacular to watch,” said Dr Black.