The icy ring around Fomalhaut

The image above shows the icy ring around the star Fomalhaut. Easily visible in the night sky, Fomalhaut is around 25 light-years from Earth. It has at least one planet, named Dagon, and as well as the ring of ice it is orbited by several inner disks of dust.

The outer icy ring, however, is more unusual. Above, you can see the outer ring in pink (in an image taken by the Atacama Large Millimetre Array) superimposed on a Hubble image of the rest of the system in blue. (The star itself is blotted out, as otherwise it would be so bright as to make the rest of the detail invisible.)

One theory about the ring proposes that it was created by violent collisions between icy comets and the building blocks of planets, while the sharp boundaries of the ring are swept out by the gravity of planets that have not yet been detected. If this is correct, the inner planets of the system are likely taking constant hits from large meteors and comets. Something similar happened in our own solar system around 4 billion years ago, during a long event known as the Late Heavy Bombardment.

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