[meteorite-list] Asteroid Juno Has A Bite Out Of It

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:29 2004
Message-ID: <200308061725.KAA13840_at_zagami.jpl.nasa.gov>

http://cfa-www.harvard.edu/press/pr0318.html

Asteroid Juno Has A Bite Out Of It
Harvard-Smithsonian Center for Astrophysics
Release No.: 03-18
For Release: August 6, 2003

Cambridge, MA -If someone sneaks a bite of your chocolate chip cookie,
they leave behind evidence of their pilferage in the form of a crescent of
missing cookie. The same is true in our solar system, where an impact can
take a bite out of a planet or moon, leaving behind evidence in the form
of a crater. By combining modern technology with a historical telescope,
astronomers have discovered that the asteroid Juno has a bite out of it.
The first direct images of the surface of Juno show that it is scarred by
a fresh impact crater.

Juno, the third asteroid ever discovered, was first spotted by astronomers
early in the 19th century. It orbits the Sun with thousands of other bits
of space rock in the main asteroid belt between Mars and Jupiter. One of
the largest asteroids, at a size of 150 miles across, Juno essentially is
a leftover building block of the solar system.

Astronomer Sallie Baliunas (Harvard-Smithsonian Center for Astrophysics)
and colleagues photographed Juno when it was located relatively nearby in
astronomical terms, about 10 percent further from the Earth than the Earth
is from the Sun. Even at that distance, Juno appeared very tiny in the
sky, subtending only 330 milli-arcseconds - the equivalent of a dime seen
at a distance of 7 miles. Imaging Juno at the high resolution needed to
resolve surface details thus presented a challenge.

To solve the problem, the scientists used an adaptive optics system
connected to the 100-inch Hooker telescope at Mount Wilson Observatory.
Adaptive optics enables astronomers to compensate for the distortion
created by air currents in our planet's atmosphere, yielding images as
sharp and clear as those taken in space.

Their surface maps showed that Juno, like other asteroids, is misshapen
rather than round, and that it has "sharp" edges. Even better, as Juno
tumbled through space during the night of observing, a "bite" came into
view - an area that appeared dark as seen at near-infrared wavelengths.
The astronomers concluded that the asteroid had recently (in astronomical
terms) collided with another object, resulting in a 60-mile-wide crater,
or possibly a smaller crater that is surrounded by a 60-mile blanket of
ejecta debris.

"I look at an asteroid as a garden - a garden not of flowers and leaves,
but one of rubble and dust churned up by constant impacts. This process of
gardening pulverizes the asteroid's surface into a fine-grained regolith,"
said Baliunas. "The recent, large impact on Juno gives us an opportunity
to see through the regolith and study excavated material from beneath the
surface - a rare look into the material out of which the early Earth was
formed."

The blast that knocked a bite out of Juno may also have provided
researchers with a convenient way of studying that asteroid up close
without ever leaving our planet. Some meteorites found on the Earth are
actually pieces of large asteroids like Juno. Those pieces were broken off
and launched into space by an impact, and then fell on our planet. The
newly-found impact crater on Juno may have sent samples of that asteroid
to the Earth.

This remarkable result demonstrates how technology can be used to renew
historical observatories, giving them a new lease on life. The Hooker
telescope, now nearing the end of its first century of observing, can use
adaptive optics systems to obtain views of the cosmos as clear as though
the telescope were in space. Hence, the telescope that Edwin Hubble and
his assistant used to discover evidence of the expanding universe
continues to make groundbreaking discoveries today.

These results were published in the May 2003 issue of the astronomy
journal Icarus.

NOTE TO EDITORS: Images associated with this release are available at:
http://cfa-www.harvard.edu/press/pr0318image.html

Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center
for Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists organized into six research divisions study the origin,
evolution, and ultimate fate of the universe.

For more information, contact:

David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
daguilar_at_cfa.harvard.edu

Christine Lafon
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
clafon_at_cfa.harvard.edu
Received on Wed 06 Aug 2003 01:25:27 PM PDT