Office of Public Relations
University of Colorado-Boulder
354 Willard Administrative Center
Campus Box 9
Boulder, Colorado 80309-0009
Henry Throop, 303-492-1628
Larry Esposito, 303-492-7325
Jim Scott, 303-492-3114
Oct. 12, 1998
COLORADO RESEARCHERS DISCOVER MISSING LINK IN PLANET FORMATION
Three University of Colorado at Boulder researchers have observed the growth
of dust particles in discs around three nearby stars, a phenomenon that
appears to be a missing link between space dust and planet formation.
Doctoral candidate Henry Throop of the department of atmospheric and
planetary sciences said some of the dust particles surrounding one "birthing
star" some 1,500 light years away in the Orion Nebula are about 100 times
larger than particles generally found in the interstellar medium. The
particles apparently are growing by accreting together, somewhat like a
snowball that picks up flakes and grows as it is rolled along the ground.
"This is the first time scientists have been directly able to see the
accretion process in the formation of planets," said Throop, who is
affiliated with CU-Boulder's Laboratory for Atmospheric and Space Physics.
"These particles are much, much bigger than they started out to be."
Images of one of the discs were taken by John Bally, director of
CU-Boulder's Center for Astrophysics and Space Astronomy, with the Hubble
Space Telescope in 1995.
The researchers used Hubble to look at the discs by using different
wavelengths of light, which bounce off the dust particles in different ways,
said Throop. The way the light scatters allows the researchers to estimate
the particle sizes.
"It's simlar to how a rainbow works," sad Throop. "The rain drops themselves
aren't dazzling colors, but we can tell some things about the drops based on
what the rainbow looks like. Likewise, by looking at the colors scattered
off these discs, we can tell something about the dust orbiting there."
A paper on the subject primarily authored by Throop was presented at the
30th annual Division for Planetary Sciences meeting in Madison, Wis., Oct.
11 to Oct 16. Co-authors include Bally, CU-Boulder Professor Larry Esposito
of LASP and Mark McCaughrean of the Astrophysical Institute in Potsdam,
When a star forms, swarms of gas and dust contract into a titanic ball,
causing the star to "turn on," said Throop. The dust ring left circling the
birthing star resembles a large doughnut.
The interstellar dust particles drawn into the ring surrounding the newborn
star initially are only about one-tenth of a micron across, Throop said. The
Hubble images showed some of the particles had grown 100 times larger -- to
10 microns, or about one-tenth the width of a human hair -- as the accretion
Located in the Milky Way, the Orion Nebula is one of the stellar nurseries
closest to Earth. The three stars under observation are each about one
million years old, Throop said.
"This is the first direct confirmation that dust particles surrounding young
stars are beginning to grow into planets," said Esposito.
"Another nifty thing going on here is that we see discs that appear to be
similar to the three we are studying around about one-third of the stars in
the Orion Nebula," said Throop. "If these similar discs are forming larger
particles, it suggests planet formation -- and thus solar systems like
ours -- may be relatively common."
The Division for Planetary Science is part of the American Astronomical
Society. Images of two of the discs are available on the website: