[meteorite-list] Asteroid Breakup Covered The Earth In Extraterrestrial Dust

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jan 18 19:03:11 2006
Message-ID: <200601190001.k0J01Y603999_at_zagami.jpl.nasa.gov>

http://www.swri.org/9what/releases/2006/Asteroid.htm

Asteroid breakup event covered the Earth in extraterrestrial dust
Southwest Research Institute (SwRI) News

Boulder, Colorado -- January 18, 2006 -- Scientists from the
California Institute of Technology (Caltech), Southwest Research
Institute (SwRI), and Charles University in the Czech Republic
have made the first positive link between a breakup event in
the main asteroid belt and a large quantity of interplanetary
dust particles deposited on Earth.

Sediments found in oceanic core samples indicate that millions
of years ago, the Earth was blanketed by extraterrestrial dust.
Computer simulations indicate these particles are fallout from
the breakup of a large asteroid in the main asteroid belt, a
population of interplanetary bodies ranging from tiny pebbles
to Texas-sized rocks located between the orbits of Mars and
Jupiter. These findings appear in the Jan. 19 issue of the journal
Nature.

Interplanetary dust is composed of bits of rock -- from a few
to several hundred microns in diameter -- produced by asteroid
collisions or ejected from comets. Interplanetary dust migrates
toward the Sun, and en route some of this dust is captured by
the Earth's gravitational field and deposited on its surface.
Presently, more than 20,000 tons of this material accumulates
on Earth each year, but the accretion rate should fluctuate
with the number of asteroid collisions and active comets. By
looking at ancient sediments that include both interplanetary
dust and ordinary terrestrial sediment, it should be possible
to detect major dust-producing solar system events in the past.

Because interplanetary dust particles are so small and rare
in sediment -- significantly less than a part per million --
they are difficult to detect using direct measurements. However
these particles are extremely rich in a rare isotope of helium
-- helium 3 -- compared with terrestrial materials. Over the
past decade, Professor Ken Farley of Caltech has measured helium
3 concentrations in sediments formed over the last 75 million
years to create a record of the interplanetary dust flux.

Recently, Farley found a large excess of helium 3 in some 8.2
million-year-old sediments, indicating that the accretion rate
of interplanetary dust suddenly increased by a factor of about
4 and then decreased over about 1.5 million years to pre-event
levels. To assure that the peak was not a fluke present at only
one site on the seafloor, two different localities were studied:
one in the Indian Ocean and one in the Atlantic. The event is
recorded clearly at both sites.

"The helium 3 spike found in these sediments is the smoking
gun that something quite dramatic happened to the interplanetary
dust population 8.2 million years ago. It's one of the biggest
dust events of the last 80 million years," says Farley.

To find the source of these particles, Dr. William F. Bottke
and Dr. David Nesvornyof the SwRI Space Studies Department
in Boulder, Colo., along with Prof. David Vokrouhlicky a visiting
scientist at SwRI from Charles University in Prague, studied
clusters of asteroid orbits that are likely the consequence
of ancient asteroidal impacts.

"While asteroids are constantly crashing into one another
in the main asteroid belt," says Bottke, "only once in a
great while does an extremely large one shatter.'

The scientists identified one cluster of asteroid fragments
whose size, age and remarkably similar orbits made it a likely
candidate for the Earth-dusting event. Tracking the orbits of
the cluster backwards in time using computer models, they found
that, 8.2 million years ago, all of its fragments shared the
same orbital orientation in space. This event defines when the
100-mile-wide asteroid called Veritas was blown apart by impact
and coincides with the spike in interplanetary seafloor sediments
described above.

"The Veritas disruption was extraordinary,' says Nesvorny.
"It was the largest asteroid collision to take place in the
last 100 million years."

As a final check, the SwRI-Czech team used computer simulations
to follow the evolution of dust particles produced by Veritas
breakup. Their work shows that the Veritas event could produce
the spike in extraterrestrial dust raining on the Earth as well
as a gradual decline in the dust flux.

"The match between our model results and the helium 3 deposits
is very compelling," Vokrouhlicky says. "It makes us wonder
whether other helium 3 peaks in oceanic cores can also be traced
back to asteroid breakups."

This research was funded by NASA's Planetary Geology and Geophysics
program and received additional financial support from the Czech
Republic grant agency and the National Science Foundation's
COBASE program. The paper, "A Late Miocene Dust Shower from
the Breakup of an Asteroid in the Main Belt" by Farley, Vokrouhlicky
Bottke and Nesvorny, aappears in the Jan. 19 issue of Nature.

Editors: High-resolution image for download is available at
http://www.swri.org/press/2006/asteroidbreakup.htm

For more information contact Deb Schmid at (210) 522-2254, Communications
Department, Southwest Research Institute, PO Drawer 28510, San
Antonio, TX 78228-0510.

For more information, contact Deb Schmid, Communications Department,
(210) 522-2046, Southwest Research Institute, PO Drawer 28510,
San Antonio, TX 78228-0510.
Received on Wed 18 Jan 2006 07:01:34 PM PST