Hubble Spots Asteroid 'Pollution,' Signs of Earth-like Planets In Star Cluster

The Hubble Space Telescope has spotted signs of Earth-like rocky planets forming in the atmospheres of burnt-out stars in a nearby star cluster, and the stars are being bombarded with debris from asteroids-like objects being drawn in by the stars' gravity.

The stars, white dwarfs - remnants of stars once like our Sun, are about 150 light years away in the Hyades star cluster in the constellation Taurus. At 625 million years old, the cluster is relatively young.

Hubble identified silicon in the atmospheres of two white dwarfs, a major ingredient of the rocky material that forms Earth and other terrestrial planets in the Solar System. This silicon may have come from asteroids that were shredded by the white dwarfs' gravity when they veered too close to the stars. The rocky debris likely formed a ring around the dead stars, which then funneled the material inwards.

The debris leads astronomers to believe that terrestrial planets were formed when these stars were born.

We have identified chemical evidence for the building blocks of rocky planets," said lead author Jay Farihi of the University of Cambridge. "When these stars were born, they built planets, and there's a good chance that they currently retain some of them. The signs of rocky debris we are seeing are evidence of this - it is at least as rocky as the most primitive terrestrial bodies in our Solar System."

The study suggests that asteroids less than 160km (100 miles) across are trapped by the stars' gravity and torn apart, raining down upon the dead stars in a form of galactic pollution that offers new insights for astronomers.

"The one thing the white dwarf pollution technique gives us that we won't get with any other planet detection technique is the chemistry of solid planets," Farihi said in a statement from Hubble.

"Based on the silicon-to-carbon ratio in our study, for example, we can actually say that this material is basically Earth-like," Farihi said.

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

 The new study is appearing in the  Monthly Notices of the Royal Astronomical Society.