[meteorite-list] Cassini VIMS Team Finds That Phoebe May Be Kin To Comets

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jun 23 13:52:38 2004
Message-ID: <200406231752.KAA07388_at_zagami.jpl.nasa.gov>

CASSINI VIMS TEAM FINDS THAT PHOEBE MAY BE KIN TO COMETS
>From Lori Stiles, UA News Services, 520-621-1877
June 23, 2004

Scientists may at last have settled the debate on the origin of
Saturn's moon, Phoebe.

Saturn long ago captured its largest outermost satellite, Phoebe, when
the moon wandered in from the frigid region beyond the orbit of Neptune
called the Kuiper belt, they conclude.

The scientists analyzed results from the Cassini Visual and Infrared
Mapping Spectrometer (VIMS) taken during the June 11 Cassini
spacecraft's Phoebe flyby. They announced the results today at a news
conference at the NASA Jet Propulsion Laboratory in Pasadena, Calif.

------------------------
Contact Information:
Robert H. Brown
520-626-9045
rhb_at_lpl.arizona.edu

Related Web site:
VIMS spectra of Phoebe
Cassini VIMS Homepage
http://wwwvims.lpl.arizona.edu/
------------------------

Scientists have long doubted that Phoebe came from the same disk of
material that formed Saturn and most of its moons. Phoebe has an
unusual orbit that is inclined to Saturn's equator, revolves backward
with respect to both Saturn's rotation and orbital motion, and travels
in the opposite direction of Saturn's other satellites.

Phoebe is widely believed to have wandered past Saturn and been
captured by that planet's mighty gravitational field. Where it wandered
from was the question.

"All our evidence leads us to conclude that Phoebe's surface is made of
water ice, water-bearing minerals, carbon dioxide, possible clays and
primitive organic chemicals in different locations on the surface,"
VIMS team member Roger N. Clark of the U.S. Geological Survey in Denver
said a few days after the flyby. "We also see spectral signatures of
materials that we have not yet identified."

It is clear that the materials in Phoebe's surface bear little
resemblance to the predominantly rocky material found in asteroids in
the belt between Mars and Jupiter. The materials that make up Phoebe
formed farther out in the solar system, where it is cold enough for
them to remain stable.

"One intriguing result of the VIMS measurements is the discovery of
possible chemical similarities between the materials on Phoebe and
those seen on comets," said VIMS team leader Robert H. Brown of the
University of Arizona.

Short period comets are thought to sit among other primitive solar
system debris in the Kuiper belt, until tugged by Neptune's gravity
toward the inner solar system.

Evidence that Phoebe might be chemically kin to comets strengthens the
case that it's similar to Kuiper Belt Objects.

The VIMS instrument is an imaging spectrometer that produces a special
data set called an image cube. It takes an image of an object in many
colors simultaneously. An ordinary video camera takes images in three
primary colors (red, green, and blue) and combines them to produce
images as seen by the human eye. The VIMS instrument takes images in
352 separate colors, spanning a realm of colors far beyond those
visible to humans. All materials reflect light in a unique way. So
molecules of any element or compound can be identified by the colors
they reflect or absorb, their "signature" spectra. The VIMS team knew
the basic chemical make-up of Phoebe only a few days after flyby.

That Phoebe likely comes from the Kuiper belt and not from the
Mars-Jupiter asteroid belt is another "first" for the Cassini mission,
Brown noted. Cassini has become the first spacecraft to flyby a Kuiper
belt object, he said.

Cassini flew by Phoebe on June 11. Cassini will conduct a critical
96-minute main-engine burn before going into orbit around Saturn on
June 30 (July 1 Universal Time). During Cassini's planned four-year
tour it will conduct 76 orbits around the Saturn system and execute 52
close encounters with seven of Saturn's 31 known moons.

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, manages the Cassini-Huygens mission for NASA's Office of
Space Science, Washington, D.C. The Cassini orbiter and its two onboard
cameras were designed, developed and assembled at JPL. The VIMS team is
based at the University of Arizona in Tucson.
Received on Wed 23 Jun 2004 01:52:26 PM PDT