Dead Stars Tell Story of Planet Birth

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory
whitney.clavin@jpl.nasa.gov

NEWS RELEASE: 2009-001 Jan. 5, 2009

Dead Stars Tell Story of Planet Birth

PASADENA, Calif. -- Astronomers have turned to an unexpected place to study the
evolution of planets -- dead stars.

Observations made with NASA's Spitzer Space Telescope reveal six dead "white dwarf"
stars littered with the remains of shredded asteroids. This might sound pretty bleak, but it
turns out the chewed-up asteroids are teaching astronomers about the building materials
of planets around other stars.

So far, the results suggest that the same materials that make up Earth and our solar
system's other rocky bodies could be common in the universe. If the materials are
common, then rocky planets could be, too.

"If you ground up our asteroids and rocky planets, you would get the same type of dust
we are seeing in these star systems," said Michael Jura of the University of California,
Los Angeles, who presented the results today at the American Astronomical Society
meeting in Long Beach, Calif. "This tells us that the stars have asteroids like ours -- and
therefore could also have rocky planets." Jura is the lead author of a paper on the findings
accepted for publication in the Astronomical Journal.

Asteroids and planets form out of dusty material that swirls around young stars. The dust
sticks together, forming clumps and eventually full-grown planets. Asteroids are the
leftover debris. When a star like our sun nears the end of its life, it puffs up into a red
giant that consumes its innermost planets, while jostling the orbits of remaining asteroids
and outer planets. As the star continues to die, it blows off its outer layers and shrinks
down into a skeleton of its former self -- a white dwarf.

Sometimes, a jostled asteroid wanders too close to a white dwarf and meets its demise --
the gravity of the white dwarf shreds the asteroid to pieces. A similar thing happened to
Comet Shoemaker Levy 9 when Jupiter's gravity tore it up, before the comet ultimately
smashed into the planet in 1994.

Spitzer observed shredded asteroid pieces around white dwarfs with its infrared
spectrograph, an instrument that breaks light apart into a rainbow of wavelengths,
revealing imprints of chemicals. Previously, Spitzer analyzed the asteroid dust around
two so-called polluted white dwarfs; the new observations bring the total to eight.

"Now, we've got a bigger sample of these polluted white dwarfs, so we know these types
of events are not extremely rare," said Jura.

In all eight systems observed, Spitzer found that the dust contains a glassy silicate
mineral similar to olivine and commonly found on Earth. "This is one clue that the rocky
material around these stars has evolved very much like our own," said Jura.

The Spitzer data also suggest there is no carbon in the rocky debris -- again like the
asteroids and rocky planets in our solar system, which have relatively little carbon.

A single asteroid is thought to have broken apart within the last million years or so in
each of the eight white-dwarf systems. The biggest of the bunch was once about 200
kilometers (124 miles) in diameter, a bit larger than Los Angeles County.

Jura says the real power of observing these white dwarf systems is still to come. When an
asteroid "bites the dust" around a dead star, it breaks into very tiny pieces. Asteroid dust
around living stars, by contrast, is made of larger particles. By continuing to use
spectrographs to analyze the visible light from this fine dust, astronomers will be able to
see exquisite details -- including information about what elements are present and in what
abundance. This will reveal much more about how other star systems sort and process
their planetary materials.

"It's as if the white dwarfs separate the dust apart for us," said Jura.

Other authors are Ben Zuckerman at the University of California, Los Angeles, and Jay
Farihi at Leicester University, England.

This research was funded by NASA and the National Science Foundation. 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://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .

-end-

To remove yourself from this mailing, please go to http://www.kintera.org/TR.asp?a=hkIXJgPUKgLXInI&s=llJ4JaNRJhLQI9MXKvF&m=krJUIZOFIiKYE

To remove yourself from all mailings from NASA Jet Propulsion Laboratory, please go to http://www.kintera.org/TR.asp?a=anJJKVNsE9KKK3L&s=llJ4JaNRJhLQI9MXKvF&m=krJUIZOFIiKYE