[meteorite-list] Phoebe's Surface Reveals Clues to its Origin

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jun 14 18:19:37 2004
Message-ID: <200406142217.PAA25746_at_zagami.jpl.nasa.gov>

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Heidi Finn (720) 974-5859
Cassini Imaging Central Laboratory for Operations
Space Science Institute, Boulder, Colo.

News Release: 2004-149 June 14, 2004

Phoebe's Surface Reveals Clues to its Origin

Images collected during Cassini's close flyby of Saturn's moon,
Phoebe, have yielded strong evidence that the tiny object may contain
ice-rich material, overlain with a thin layer of darker material
perhaps 300 to 500 meters (980 to 1,600 feet) thick.

The surface of Phoebe is also heavily potholed with large and small
craters. Images reveal
bright streaks in the ramparts of the largest craters, bright rays
which emanate from smaller craters, and uninterrupted grooves across
the face of the body.

"The imaging team is in hot debate at the moment on the
interpretations of our findings," said Dr. Carolyn Porco, Cassini
imaging team leader at the Space Science Institute in Boulder, Colo.
"Based on our images, some of us are leaning towards the view that has
been promoted recently, that Phoebe is probably ice-rich and may be an
object originating in the outer solar system, more related to comets
and Kuiper Belt objects than to asteroids."

In ascertaining Phoebe's origin, imaging scientists are noting
important differences between the surface of Phoebe and that of rocky
asteroids which have been seen at comparable resolution. "Asteroids
seen up close, like Ida, Mathilde, and Eros, and the small martian
satellites do not have the bright 'speckling' associated with the
small craters that are seen on Phoebe," said Dr. Peter Thomas, an
imaging team member from Cornell University, Ithaca, N.Y.

The landforms observed in the highest resolution images also contain
clues to the internal structure of Phoebe. Dr. Alfred McEwen, an
imaging team member from the University of Arizona, Tucson, said,
"Phoebe is a world of dramatic landforms, with craters everywhere,
landslides, and linear structures such as grooves, ridges, and chains
of pits. These are clues to the internal properties of Phoebe, which
we'll be looking at very closely in order to understand Phoebe's
origin and evolution."

"I think these images are showing us an ancient remnant of the bodies
that formed over four billion years ago in the outer reaches of the
solar system," said Dr. Torrence Johnson, an imaging team member from
NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Battered and
beat-up as it is, it is still giving us clues to its origin and
history."

Phoebe may be an icy interloper from the distant outer solar system
which found itself captured by giant Saturn in its earliest, formative
years. Final conclusions on Phoebe's origins await a combination of
the results on Phoebe's surface structures, mass and composition
gathered from all 11 instruments, which collected data during the
flyby on June 11, 2004.

"This has been an impressive whirlwind flyby and it's only a curtain
raiser on the events about to begin," said Porco.

Cassini arrives in orbit around Saturn on the evening of June 30, 2004
(July 1 Universal Time).
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, 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 imaging team is based
at the Space Science Institute, Boulder, Colo.

For the latest images and information about the Cassini-Huygens
mission, visit

http://saturn.jpl.nasa.gov

and the Cassini imaging team home page,

http://ciclops.org .

For more information on NASA programs, visit

http://www.nasa.gov .

-end-
Received on Mon 14 Jun 2004 06:17:48 PM PDT