First Observation Of
Earth-Like Planet Formation
(13 March 2008) For the first time,
astronomers have observed the initial phase in the formation of an earth-like
planet.
The discovery, highlighted in the March 13th issue of
Nature, was documented by a team of astronomers led by William Herbst, the Van
Vleck Professor of Astronomy professor at Wesleyan, and Catrina Hamilton PhD
'03, professor of physics and astronomy at Dickenson College.
What
Herbst and other astronomers on his team observed was that a protoplanitary
disk, or ring, around the binary star known as KH 15D, is composed of solid
particles larger than what is usually observed in space.
"For hundreds
of years, scientists have been theorising that Earth-like planets form when gas
and dust around a star get compressed into these disks and the material begins
to coalesce into planets. But until now we never had the ability to study this
process in detail," Herbst said. "The unique geometry presented by KH 15D and
the way the light was being reflected off the disk allowed us to get a good
look at the structure of the disk We were amazed at what we saw."
The
disk orbiting KH 15D is at least the size of Jupiter's orbit and composed of
sand-sized grains that have grown from microscopic-sized particles to form the
larger grains. These grains are now approximately 1 mm in diameter, much larger
than the tiny particles typically seen in space. This is also the
characteristic size of "chondrules," small glassy spherules that are found in
the most primitive solar system, the so-called carbonaceous chondrite
meteorites.
The observations of the disk were made over several years
using some of the largest telescopes in the world, including the 10-metre
telescope of the W.M. Keck Observatory in Hawaii. More modest telescopes,
including the one at Wesleyan University's Van Vleck observatory and the
Maidanak Observatory in Uzbekistan, were also used in the study.
Located
approximately 2,400 light years from earth and also known within the
astronomical community as the "winking star," KH 15D was first documented in
1995 by Herbst and his then-graduate student Kristin Kearns. An ensuing Ph.D.
thesis by Herbst student Catrina Hamilton, now on the faculty of Dickenson
College, further solidified the importance of this star and brought it to the
attention of the astronomical community. In 2004, two groups of astronomers on
opposite coasts showed that KH 15D's winking was a result binary star with an
orbiting period of 48.36 days within a large disk. The winking effect was
generated as one of the stars alternately rose above and set below the
disk.
What Herbst, Hamilton and the rest of the team observed recently
is that the disk is slowly hiding the stars from view and putting them in a
permanent state of faintness, though still visible by the reflection off the
disk.
"Because of how the light is being reflected there are
opportunities to make observations about the chemical composition of these
sand-like particles," Herbst said. "That's very exciting because it opens up so
many doors for new type of research on this disk."
Herbst is the Chair
and Van Vleck Professor of Astronomy at Wesleyan University. The members of
Herbst's team documenting the observations include Catrina Hamilton, who
received her Ph.D. degree in Physics from Wesleyan University in 2003 with
Herbst as her advisor and is now on the faculty of Dickinson College; Katherine
LeDuc, M.A.'07; Joshua N. Winn of M.I.T.; Christopher M. Johns-Krull of Rice
University; Reinhard Mundt of the Max-Planck-Institute for Astronomy in
Heidelberg, Germany; and Mansur Ibrahimov of the Ulugh Bek Astronomical
Institute in Tashkent, Uzbekistan. Support for the work has come over the years
from NASA's Origins of Solar Systems program and from the W. M. Keck
Observatory Principal Investigator's Fund.
(source: Wesleyan
University)
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