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Pulverized planet dust may lie around double stars

Scientists believe that planetary collisions are kicking up fresh dust.
Provided by the Jet Propulsion Laboratory, Pasadena, California
Planetary collision
This artist's concept illustrates an imminent planetary collision around a pair of double stars.
JPL/NASA
August 24, 2010
Tight double-star systems might not be the best places for life to spring up, according to a new study using data from NASA's Spitzer Space Telescope. The infrared observatory spotted a surprisingly large amount of dust around three mature, close-orbiting star pairs. Where did the dust come from? Astronomers say it might be the aftermath of tremendous planetary collisions.

"This is real-life science fiction," said Jeremy Drake from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "Our data tell us that planets in these systems might not be so lucky — collisions could be common. It's theoretically possible that habitable planets could exist around these types of stars, so if there happened to be any life there, it could be doomed."

The particular class of binary stars in the study is about as snug as stars get. Named RS Canum Venaticorums, (RS CVns) they are separated by only about 2 million miles (3.2 million kilometers), or 2 percent of the distance between Earth and our Sun. The stellar pairs orbit around each other every few days, with one face on each star perpetually locked and pointed toward the other.

The close-knit stars are similar to the Sun in size and are probably about a billion to a few billion years old — roughly the age of our Sun when life first evolved on Earth. But these stars spin much faster and, as a result, have powerful magnetic fields and giant, dark spots. The magnetic activity drives strong stellar winds — gale-force versions of the solar wind — that slow the stars down, pulling the twirling duos closer over time. This is where the planetary chaos may begin.

As the stars cozy up to each other, their gravitational influences change, and this could cause disturbances to planetary bodies orbiting around both stars. Comets and any planets that may exist in the systems would start jostling about and banging into each other, sometimes in powerful collisions. This includes planets that could theoretically be circling in the double stars' habitable zone, a region where temperatures would allow liquid water to exist. Although no habitable planets have been discovered around any stars beyond our Sun at this point in time, tight double-star systems are known to host planets.

"These kinds of systems paint a picture of the late stages in the lives of planetary systems," said Marc Kuchner from NASA's Goddard Space Flight Center in Greenbelt, Maryland. "And it's a future that's messy and violent."

Spitzer spotted the infrared glow of hot dusty disks, about the temperature of molten lava, around three such tight binary systems. The Infrared Astronomical Satellite originally flagged one of the systems as having a suspicious excess of infrared light in 1983. In addition, researchers using Spitzer recently found a warm disk of debris around another star that turned out to be a tight binary system.

The astronomy team says that dust normally would have dissipated and blown away from the stars by this mature stage in their lives. They conclude that something, most likely planetary collisions, must therefore be kicking up the fresh dust. In addition, because dusty disks have now been found around four older binary systems, scientists know that the observations are not a fluke. Something chaotic is likely going on.
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