[meteorite-list] Vesta meteorite???

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:27:53 2004
Message-ID: <200311261656.IAA16156_at_zagami.jpl.nasa.gov>

CONTACT: Don Savage
          NASA Headquarters, Washington, DC
          (Phone: 202-358-1547)

          Tammy Jones
          Goddard Space Flight Center, Greenbelt, MD
          (Phone: 301-286-5566)

          Ray Villard
          Space Telescope Science Institute
          (Phone: 410-338-4514)

PRESS RELEASE NO.: STScI-PR95-20


                         ASTEROID OR MINI-PLANET?
                 HUBBLE MAPS THE ANCIENT SURFACE OF VESTA

NASA's Hubble Space Telescope images of the asteroid Vesta are
providing astronomers with a glimpse of the oldest terrain ever seen
in the solar system and a peek into a broken off section of the
"mini-planet" that exposes its interior.

Hubble's pictures provide the best view yet of Vesta's complex surface,
with a geology similar to that of terrestrial worlds such as Earth or
Mars. The asteroid's ancient surface, battered by collisions eons ago,
allows astronomers to peer below the asteroid's crust and into the
past.

Astronomers also believe that fragments gouged out of Vesta during
ancient collisions have fallen to Earth as meteorites, making Vesta
only the fourth solar system object, other than Earth, the Moon and
Mars, where scientists have a confirmed laboratory sample. (About
50-60 other meteorite types are suspected to have come from asteroids,
but positive identifications are more difficult to make.)

"The Hubble observations show that Vesta is far more interesting than
simply a chunk of rock in space as most asteroids are," said Ben
Zellner of Georgia Southern University. "This qualifies Vesta as the
'sixth' terrestrial planet."

No bigger than the state of Arizona, Vesta offers new clues to the
origin of the solar system and the interior makeup of the rocky
planets. "Vesta has survived essentially intact since the formation of
the planets," Zellner said. "It provides a record of the long and
complex evolution of our solar system."

Resolving features down to 50 miles across, Hubble reveals a
surprisingly diverse world with an exposed mantle, ancient lava flows
and impact basins. Though only 325 miles (525 kilometers) across, it
once had a molten interior. This contradicts conventional ideas that
asteroids essentially are cold, rocky fragments left behind from the
early days of planetary formation.

Besides providing scientists with direct samples, Vesta's chipped
surface allows Hubble to study the asteroid's rocky mantle, giving
scientists a unique opportunity to see what a planet looks like below
the crust. "Our knowledge of the interior composition of the other
terrestrial worlds, the Moon, Mars, Venus, Mercury and even Earth,
depends heavily on theory and inference," Zellner said. "Vesta allows
us to actually see the mantle and study pristine samples in our
laboratories."

Before these observations, only the smaller and less geologically
diverse asteroids, Ida and Gaspra, have been observed in detail by the
Jupiter-bound Galileo spacecraft. Unlike Vesta, these smaller objects
are pieces torn off larger bodies by collisions that occurred perhaps
only a few hundred million years ago.

                                 * * * * *

The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA) for NASA, under
contract with the Goddard Space Flight Center, Greenbelt, MD. The
Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).

NOTE TO EDITORS: Image files in GIF and JPEG format may be accessed on
Internet via anonymous ftp from ftp.stsci.edu in /pubinfo:
        
                 GIF JPEG
Vesta 24 frames /pubinfo/gif/Vesta24.gif /pubinfo/jpeg/Vesta24.jpg
Vesta Meteorite /pubinfo/gif/VestMet.gif /pubinfo/jpeg/VestMet.jpg

The same images are available via World Wide Web from links in URL
http://www.stsci.edu/public.html, or more directly from
http://www.stsci.edu/Latest.html.

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

                            SCIENCE BACKGROUND


                         "ASTEROID OR MINI-PLANET?
                 HUBBLE MAPS THE ANCIENT SURFACE OF VESTA"


VESTA: THE SIXTH TERRESTRIAL PLANET?

Vesta is the most geologically diverse of the large asteroids and the
only known one with distinctive light and dark areas -- much like the
face of our Moon. Previous ground-based spectroscopy of Vesta
indicates regions that are basaltic, which means lava flows once
occurred on its surface. This is surprising evidence that the asteroid
once had a molten interior, like Earth does.

One possibility is that Vesta agglomerated from smaller material that
includes radioactive debris (such as the the isotope Aluminum-26) that
was incorporated into the core. This radioactive "shrapnel" probably
came from a nearby supernova explosion. (In fact a supernova might
have triggered the birth of our solar system.) This hot isotope may
have melted the core, causing the asteroid to differentiate: heavier,
dense material sank to the center while lighter rock rose to the
surface. This is a common structure for the terrestrial planets.
After Vesta's formation, molten rock flowed onto the asteroid's
surface. This happened more than four billion years ago. The surface
has remained unchanged since then, except for occasional meteoroid
impacts.

One or more large impacts tore away some of the crust exposing a deeper
mantle of olivine, which is believed to constitute most of the Earth's
mantle. Some of the pieces knocked off Vesta have fallen to Earth as
meteorites, which show a similar spectral fingerprint to Vesta's
surface composition.


A PIECE OF VESTA FALLS TO EARTH

In October 1960, two fence workers in Millbillillie, Western Australia,
observed a fireball heading toward the ground, and pieces of the fallen
meteorite were found ten years later. The fragments stood out from the
area's reddish sandy soil because they had a shiny black fusion crust,
produced by their fiery entry through Earth's atmosphere.

Unlike most other meteorites, this sample can be traced to its parent
body, the asteroid Vesta. The meteorite's chemical identity points to
Vesta because it has the same unique pyroxene spectral signature.
Pyroxine is common in lava flows, meaning that the meteorite was
created in an ancient lava flow on Vesta's surface. The structure of
the meteorite's mineral grains also indicates it was molten and then
cooled. The isotopes (oxygen atoms with varying number of neutrons)
in the specimen are unlike the isotopes found for all other rocks of
the Earth, Moon and most other meteorites.

The meteorite also has the same pyroxene signature as other small
asteroids, recently discovered near Vesta, that are considered chips
blasted off Vesta's surface. This debris extends all the way to an
escape hatch region in the asteroid belt called the Kirkwood gap.
This region is swept free of asteroids because Jupiter's gravitational
pull removes material from the main belt and hurls it onto a new orbit
that crosses Earth's path around the Sun.

The Australian meteorite probably followed this route to Earth. It was
torn off Vesta's surface as part of a larger fragment. Other
collisions broke apart the parent fragment and threw pieces toward the
Kirkwood gap, and onto a collision course toward Earth. Meteorites
found in other locations on Earth are probably from Vesta too.


THE OBSERVATION

Ben Zellner (Georgia Southern University), Alex Storrs (Space Telescope
Science Institute Baltimore, MD), Ed Wells (Computer Sciences
Corporation, Bethesda, MD), Rudi Albrecht (European Southern
Observatory in Garching bei Munchen, Germany) and collaborators used
Hubble's Wide Field and Planetary Camera 2 (WFPC 2) to collect images
of Vesta in four colors of light between November 28 and December 1,
1994. At the time Vesta was 156 million miles (252 million km) from
Earth. In late December 1994, when Vesta was 10 million miles (16
million km) closer to Earth than a month earlier, HST's Faint Object
Camera made even higher resolution images. These results are
complemented by infrared observations made on December 11, by Olivier
Hainaut and colleagues with an adaptive- optics camera on the European
Southern Observatory's 3.6-meter telescope in Chile. By combining
Hubble and ESO observations astronomers will be able to produce a
geochemical map of an asteroid's surface.
Received on Wed 26 Nov 2003 11:56:15 AM PST