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Re: Ibitira update

I wrote:
>The parent body of all eucrites is strongly
>suspected to be the asteroid
>Vesta.  This is based on spectra which match up surprisingly well between
>eucrites and Vesta.  Hubble Space Telescope images of the asteroid
>also shows evidence of lava flows, which fits in well with eucrites
>since they are basaltic rocks.  

Several people have asked me if these Hubble images of Vesta are available on
the Internet, and the are.  They are available on the following home pages:

http://oposite.stsci.edu/pubinfo/PR/95/20.html
http://oposite.stsci.edu/pubinfo/PR/95/40.html

I've also appended the NASA press release that came out in 1995 with the
release of the Hubble images.

Included with the Hubble images is a photo of a eucrite meteorite,
Millbillillie.  Note the nice shiny, glossy fusion crust on the meteorite. 
This type of fusion crust is a feature characteristic of eucrites.  
This glossy fusion crust is beautifully shown in these photos of the Ibitira 
meteorite taken by Michael Blood:

http://www.meteorite.com/Michael_Blood/ibitira3.jpg
http://www.meteorite.com/Michael_Blood/ibitira5.jpg

Ron Baalke

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                            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.
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