[meteorite-list] Ceres May Be 'Mini Planet' with Water Ice

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Sep 7 15:40:10 2005
Message-ID: <200509071939.j87Jd5Q12926_at_zagami.jpl.nasa.gov>

http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/27/text/

Release Number: STScI-2005-27

Contact:

Dolores Beasley
NASA Headquarters, Washington
(Phone: 202/358-1753)

Susan Hendrix
Goddard Space Flight Center, Greenbelt, Md
(Phone: 301/286-7745)

Donna Weaver
Space Telescope Science Institute, Baltimore
(Phone: 410-338-4493)

Largest Asteroid May Be 'Mini Planet' with Water Ice
September 7, 2005

Observations of 1 Ceres, the largest known asteroid, have revealed that
the object may be a "mini planet," and may contain large amounts of pure
water ice beneath its surface.

The observations by NASA's Hubble Space Telescope also show that Ceres
shares characteristics of the rocky, terrestrial planets like Earth.
Ceres' shape is almost round like Earth's, suggesting that the asteroid
may have a "differentiated interior," with a rocky inner core and a
thin, dusty outer crust.

"Ceres is an embryonic planet," said Lucy A. McFadden of the Department
of Astronomy at the University of Maryland, College Park and a member of
the team that made the observations. "Gravitational perturbations from
Jupiter billions of years ago prevented Ceres from accreting more
material to become a full-fledged planet."

The finding will appear Sept. 8 in a letter to the journal Nature. The
paper is led by Peter C. Thomas of the Center for Radiophysics and Space
Research at Cornell University in Ithaca, N.Y., and also includes
project leader Joel William Parker of the Department of Space Studies at
Southwest Research Institute in Boulder, Colo.

Ceres is approximately 580 miles (930 kilometers) across, about the size
of Texas. It resides with tens of thousands of other asteroids in the
main asteroid belt. Located between Mars and Jupiter, the asteroid belt
probably represents primitive pieces of the solar system that never
managed to accumulate into a genuine planet. Ceres comprises 25 percent
of the asteroid belt's total mass. However, Pluto, our solar system's
smallest planet, is 14 times more massive than Ceres.

The astronomers used Hubble's Advanced Camera for Surveys to study Ceres
for nine hours, the time it takes the asteroid to complete a rotation.
Hubble snapped 267 images of Ceres. From those snapshots, the
astronomers determined that the asteroid has a nearly round body. The
diameter at its equator is wider than at its poles. Computer models show
that a nearly round object like Ceres has a differentiated interior,
with denser material at the core and lighter minerals near the surface.
All terrestrial planets have differentiated interiors. Asteroids much
smaller than Ceres have not been found to have such interiors.

The astronomers suspect that water ice may be buried under the
asteroid's crust because the density of Ceres is less than that of the
Earth's crust, and because the surface bears spectral evidence of
water-bearing minerals. They estimate that if Ceres were composed of 25
percent water, it may have more water than all the fresh water on Earth.
Ceres' water, unlike Earth's, would be in the form of water ice and
located in the mantle, which wraps around the asteroid's solid core.

Besides being the largest asteroid, Ceres also was the first asteroid to
be discovered. Sicilian astronomer Father Giuseppe Piazzi spotted the
object in 1801. Piazzi was looking for suspected planets in a large gap
between the orbits of Mars and Jupiter. As more such objects were found
in the same region, they became known as "asteroids" or "minor planets."

------------------------------------------------------------------------

http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/27/image/a

Hubble Tracks Ceres

STScI-PRC2005-27

NASA's Hubble Space Telescope took these images of the asteroid 1 Ceres
over a 2-hour and 20-minute span, the time it takes the Texas-sized
object to complete one quarter of a rotation. One day on Ceres lasts 9
hours.

Hubble snapped 267 images of Ceres as it watched the asteroid make more
than one rotation. By observing the asteroid during a full rotation,
astronomers confirmed that Ceres has a nearly round body like Earth's.
Ceres' shape suggests that its interior is layered like those of
terrestrial planets such as Earth. Ceres may have a rocky inner core, an
icy mantle, and a thin, dusty outer crust inferred from its density and
rotation rate.

The bright spot that appears in each image is a mystery. It is brighter
than its surroundings. Yet it is still very dark, reflecting only a
small portion of the sunlight that shines on it.

Ceres is approximately 580 miles (930 kilometers) across and is the
largest known asteroid. It resides with tens of thousands of other
asteroids in a region between the orbits of Mars and Jupiter called the
main asteroid belt. Besides being the largest asteroid, Ceres also was
the first to be discovered, in 1801.

Astronomers enhanced the contrast in these images to bring out important
features on Ceres' surface. The observations were made in visible and in
ultraviolet light. Hubble took the snapshots between December 2003 and
January 2004.

Credit: NASA, ESA, J. Parker (Southwest Research
Institute), P. Thomas (Cornell University), and L. McFadden (University
of Maryland, College Park)

Image Type: Astronomical
STScI-PRC2005-27
Received on Wed 07 Sep 2005 03:39:05 PM PDT