[meteorite-list] Asteroids, Comets, Planets: Cut From Same Cloth?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Oct 10 13:54:49 2006
Message-ID: <200610101754.KAA28746_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/features.cfm?feature=1199

Asteroids, Comets, Planets: Cut From Same Cloth?
Written by Linda Vu, Spitzer Science Center
Media contact: Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
October 10, 2006

Could all of the asteroids, comets, and planets in our Milky Way galaxy
be made of a similar mix of dusty components?

After analyzing the dust particles of a variety of comets with NASA's
Spitzer Space Telescope, the Deep Impact spacecraft and the
internationally funded Infrared Space Observatory, Dr. Carey Lisse, of
the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.,
suspects that the answer is yes.

"Comets are the stepping stones to planets," said Lisse. "With these
missions, astronomers know more about comets today than ever before, and
we're still only beginning to scratch the surface."

He presents his findings today at the 38th meeting of the Division for
Planetary Sciences of the American Astronomical Society in Pasadena, Calif.

According to Lisse, the Deep Impact mission, which sent an 820-pound
impactor into the path of a hurtling comet about 5 by 8 kilometers (3 by
5 miles) wide, provided a "Rosetta stone" for studying solar system
formation in the universe. The collision, on July 4, 2005, unleashed a
plethora of pristine particles that had been locked in the core of comet
Tempel 1 since the dawn of our solar system.

>From its lofty perch in space, Spitzer was in the perfect position to
scrutinize the cometary material ejected from comet Tempel 1. The
sensitive telescope's spectrometer instrument detected dust particles
finer than human hair, and discovered the presence of silicates (crushed
rock or sand), carbonates (chalk), smectite (clay), metal sulfides (like
fool's gold), amorphous carbon (soot) and polycyclic aromatic
hydrocarbons (carbon-rich molecules found on barbecue grills and in
automobile exhaust on Earth).

Scientists have determined that comet Tempel 1 is a loosely assembled
icy dirtball with the consistency of talcum powder. "The impactor was
able to go 20 to 30 meters into the comet and release material that
hadn't been baked or boiled by the comet's previous trips around the
sun," said Lisse.

Lisse and his team later compared their Tempel 1 data to observations of
comet Hale Bopp made by the Infrared Space Observatory in 1997. Although
Hale Bopp did not show any of the iron-rich olivine silicates found in
Tempel 1, team members did find many chemical similarities, like ice
made of water, carbonates, sulfides, polycyclic aromatic hydrocarbons
and other types of silicates.

They then looked at the Infrared Space Observatory's observations of a
distant solar system called HD 100546, which many scientists believe is
undergoing planet formation, and again found many of the materials
observed in Hale Bopp and Tempel 1. However, unlike the comets, HD
100546 didn't contain some of the most primitive rock-forming elements.

"Although there are some particle variations, our team has found that
Tempel 1, Hale Bopp and HD100546 share many of the same basic chemical
compounds," said Lisse. "We think the differences we see are due to the
effect of active planet formation, nebular shocks, and collisions in the
HD100546 planet-forming disk."

In a new extension of this work, Lisse recently teamed with Dr. Charles
Beichman of NASA's Jet Propulsion Laboratory in Pasadena, Calif., to
study HD69830, a star surrounded by a disk of dusty material and three
Neptune-sized planets. Previously, Beichman and his colleagues suspected
the disk could be an asteroid belt. Now, the astronomers have used
Lisse's models of planetary body ingredients to confirm that the disk is
an asteroid belt, and to show that it may have been created by the
destruction of an icy asteroid about 70 kilometers across (43 miles).
This is similar to what happened in our own solar system millions of
years ago. In addition, the new analysis reveals that the asteroid belt
is twice as far out as previously believed, beyond the known planets.

"I am thrilled by these findings. This is one of the first steps to
realizing that our solar system may be similar to other solar systems in
the universe," he said.

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. Spitzer's infrared spectrograph was built
by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim
Houck of Cornell.

For more information and graphics, visit

www.spitzer.caltech.edu/spitzer .
Received on Tue 10 Oct 2006 01:54:29 PM PDT