A cosmic catastrophe is likely for one of Mars' moons, Phobos. Astronomers have calculated that in about 50 million years the small moon will break up and form a ring around the red planet.

Strange cracks have appeared on the surface of Phobos, one of Mars' moons. They have been known to astronomers since the 1970s, when space probes transmitted the first close-up images.

The researchers suspected that they could be expansion cracks caused by the tidal forces of Mars. Recent computer simulations have now confirmed this assumption.

The tidal forces, a result of the gravitational interaction between Mars and Phobos, are so great that the planet is slowly tearing apart its moon. The distance between the moon and Mars is already decreasing by almost two centimetres every year.

This same phenomenon also occurs between the earth and the moon, but, unlike with Phobos, there is no danger that our moon could break under these forces.

In the case of Phobos, astronomers assume that the moon will break up in about 50 million years. Some of its debris will then crash onto Mars, while smaller fragments and dust will collect in a low orbit and eventually form rings similar to those surrounding Saturn.