Clues to Planet Formation Revealed

http://www.umich.edu/news/index.html.../May05/r052305

Clues to planet formation revealed
University of Michigan News Service
May 23, 2005

ANN ARBOR, Mich. - The most detailed measurements to date of the dusty
disks around young stars confirm a new theory that the region where
rocky planets such as Earth form is much farther away from the star
than
originally thought.

These first definitive measurements of planet-forming zones offer
important clues to the initial conditions that give birth to planets.
Understanding planet formation is key to understanding Earth's origins,
yet this remains a mysterious process, said John Monnier, assistant
professor of astronomy at the University of Michigan and lead author on
the paper, "The near-infrared size luminosity relations for Herbig
Ae/Be
disks" in a recent edition of Astrophysical Journal.

Very young stars are surrounded by thick, rotating disks of gas and
dust, which are expected to eventually disappear as material is either
pulled into the star, is blown from the disk, or collects into larger
pieces of debris. This transition marks the leap from star formation to
planet formation.

The scientists examined the innermost region of such disks where the
star's energy heats the dust to extremely high temperatures. These
dusty
disks are where the seeds of planets form, where dusty particles stick
together and eventually grow to large masses.

However, if the dust orbits too close to the star, it evaporates,
shutting off any hope of planet formation. It's important to know where
the evaporation begins since it has a dramatic effect on planet
formation, Monnier said. The initial temperature and density of dust
surrounding young stars are critical ingredients for advanced computer
models of planet formation.

For the study, scientists looked at young stars that are about one and
a
half times the mass of the sun. "We can study these stars more in-depth
because they are brighter and easier to see," Monnier said.

In the last decade or so, beliefs about the systems that build planets
have changed drastically with the onset of powerful observatories that
can take more precise measurements, Monnier said.

They found that measurements thought to be accurate were actually very
different than originally thought.

For this work, scientists used the two largest telescopes in the world
linked together to form the Keck Interferometer. This ultra-powerful
duo
acts as the ultimate zoom lens allowing astronomers to peer into
planetary nurseries with 10X the detail of the Hubble Space Telescope.
By combining the light from the two Keck Telescopes, researchers were
able to achieve the capabilities of a single telescope that spans a
football field, but for a fraction of the cost, Monnier said.

Other key authors were Rafael Millan-Gabet and Rachel Akeson of the
Michelson Science Center. Other key institutions included the
Caltech-run, NASA Jet Propulsion Laboratory and the W.M. Keck
Observatory in Kamuela, Hawaii.

The Keck Interferometer was funded by NASA and developed and operated
by
Jet Propulsion Lab, W.M. Keck Observatory, and the Michelson Science
Center.

For more information on Monnier, visit:
http://www.astro.lsa.umich.edu/~monnier/

For U-M Department of Astronomy, visit:
http://www.astro.lsa.umich.edu

For the Keck Observatory, visit:
http://www2.keck.hawaii.edu/


Contact: Laura Bailey
Phone: (734) 647-7087 or (734) 647-1848
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