Nearby Star System Could Spawn Carbon-Rich Planets

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Roberge and her colleagues used NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and the Hubble Space Telescope to measure the gases. They found an unexpectedly high quantity of carbon gas—about 20 times more than in our own solar system.

Carbon "doesn't get blown away like other gases do, and if there's enough, it can bind the other gases to the star," Roberge said.

"Our measurements show more than enough [carbon] for that to work—to keep them in orbit instead of being blown away."

She and her colleagues report the finding in tomorrow's issue of the journal Nature.

Carbon Source

The finding, however, does not explain what put the carbon there in the first place. Roberge says scientists have several ideas.

Conel Alexander is a cosmochemist in the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, D.C. He explored two of the possibilities in a telephone call with reporters.

"Perhaps because Beta Pictoris is such a young system, what we're seeing is a snapshot of what occurred in [our] early solar system as the asteroids were degassing, while the [life-forms] in them were being cooked in their interiors," he said.

Alternatively, he said, the carbon may be leftover gas that failed to condense after the energetic collisions of planet-forming asteroids and comets.

But neither explanation, he adds, is explained by the current observations.

"We need to at least consider a more exotic explanation," he said.

Marc Kuchner studies planet formation at the Goddard Space Flight Center. He suggests that the carbon-rich planets forming around Beta Pictoris are unlike those in our solar system.

The Beta Pictoris carbon planets would have a core composed of iron, nickel, and carbon, he says. Closer to the surface, but still deep underground, might be a layer of graphite.

"Of course graphite wouldn't exist deep underground," he said. "Like coal, graphite would change into diamond at high pressures."

The surface of such a planet would be covered in tar, soot, and other carbon-rich materials.

If any life existed on such a planet, it would survive by consuming oxygen-rich foods and using carbon to derive energy from them—the reverse of what we do on Earth.

"Maybe Beta Pictoris is a glimpse at the history of our own solar system," he said.

"Or maybe instead Beta Pictoris is telling us about the startling variety of other kinds of planetary systems that might be out there."

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