Pulverized Planet Dust May Lie Around Double Stars

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
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News release: 2010-275 Aug. 23, 2010

Pulverized Planet Dust May Lie Around Double Stars

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-275&cid=release_2010-275


PASADENA, Calif. -- 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 of the Harvard-Smithsonian Center for
Astrophysics, Cambridge, Mass. "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."

Drake is the principal investigator of the research, published in the Aug.19 issue of the
Astrophysical Journal Letters.

The particular class of binary, or double, stars in the study are about as snug as stars get. Named
RS Canum Venaticorums, or RS CVns for short, they are separated by only about two-million
miles (3.2-million kilometers), or two 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. And 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. Though 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; for example, one system not in the study,
called HW Vir, has two gas-giant planets.

"These kinds of systems paint a picture of the late stages in the lives of planetary systems," said
Marc Kuchner, a co-author from NASA Goddard Space Flight Center in Greenbelt, Md. "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. One of the systems was originally flagged as having a
suspicious excess of infrared light in 1983 by the Infrared Astronomical Satellite. 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, the scientists know that the observations are
not a fluke. Something chaotic is very likely going on.

If any life forms did exist in these star systems, and they could look up at the sky, they would
have quite a view. Marco Matranga, first author of the paper, from the Harvard-Smithsonian
Center for Astrophysics and now a visiting astronomer at the Palermo Astronomical Observatory
in Sicily, said, "The skies there would have two huge suns, like the ones above the planet
Tatooine in 'Star Wars.'"

Other authors include V.L. Kashyap of the Harvard-Smithsonian Center for Astrophysics; and
Massimo Marengo of Iowa State University, Ames.

The Spitzer observations were made before it ran out of its liquid coolant in May 2009, officially
beginning its warm mission.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science operations are conducted
at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech
manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu/
and http://www.nasa.gov/spitzer .

The Infrared Astronomical Satellite, known commonly by its acronym, IRAS, was a joint project
between NASA, the Netherlands and the United Kingdom.

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