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Astronomers find distant planetary dust-up

planet smashup

The researchers believe the collision that produced the dust around the binary system occurred less than a 1000 years ago (Source: Gemini/Jon Lomberg)

US astronomers have discovered that a pair of stars shrouded in a cloud of debris aren't part of a newly forming solar system, but are witnesses to a massive planetary dust-up.

The team, led by Professor Ben Zuckerman from the University of California, Los Angeles, has found that the binary star system BD+20 307 is "several-to-many" billion years old - well into its later years of evolution.

The research appears on the physics website arxiv and has been accepted for publication in the Astrophysical Journal.

Solar systems are thought to form from protoplanets or planetesimals coalescing from the dusty disk surrounding young stars.

Previously, astronomers examining BD+20 307 thought the binary star system was only 300 million years old, and that the dusty disk may have been a solar system in the early stages of formation.

Studies of the light scattered by dust surrounding the stars shows the density of the dust is one million times denser than in our own solar system.

The astronomers measured the mass and brightness of the stars using the orbiting Chandra x-ray observatory and the Fairborn Observatory in Arizona.

They found that the abundance of lithium and other metals, as well as the stars' luminosity and temperature, "points to an old age", says Zuckerman.

"Various methods taken together seem to imply a BD+20 307 age of [at] least a few billion years, and possibly considerably more," the researchers write.

They conclude that the dust cloud surrounding the binary star system is unlikely to have "any direct relationship with the origin of terrestrial planets."

But they do add that the dust may point towards the presence of terrestrial planets - the first known example of planets of any kind orbiting a close binary system.

Bumped out of orbit

Zuckerman believes the collision that produced the dust must have been massive.

"The collision of earth with an asteroid 65 million years ago, which apparently finished off the dinosaurs, would have been miniscule by comparison," says Zuckerman.

The amount of dust still orbiting around the stars indicates the collision occurred less than 1000 years ago.

Zuckerman says the collision may have come about because the orbits of rocky planets are more easily destabilised near a double star than near a single star.

He says his team had searched for a third star in unpublished research, but so far have found no sign of one.

Dr John Greenhill, a physicist at the University of Tasmania in Hobart and member of the worldwide PLANET (Probing Lensing Anomalies NETwork) collaboration, says the research is a "convincing bit of work and a clue to the formation and evolution of planets around other stars".

"Nobody has found anything [else] around binary systems and that's interesting in itself," says Greenhill.

Greenhill says the extra solar planets that have been found so far indicate other solar systems are much more exotic than our own.

"This [research] sheds more light into what's going on within planetary systems and that's important," he says.

"It is another indication [that] our current theories about the formation of solar systems are inadequate."

To date, more than 300 extra solar planets have been found, including seven that may have an earth-like mass.
