[meteorite-list] NASA's WISE Raises Doubt About Asteroid Family Believed Responsible for Dinosaur Extinction

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 19 Sep 2011 11:33:55 -0700 (PDT)
Message-ID: <201109191833.p8JIXt7f008366_at_zagami.jpl.nasa.gov>

Sept. 19, 2011

Trent J. Perrotto
Headquarters, Washington
202-358-0321
trent.j.perrotto at nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin at jpl.nasa.gov
RELEASE: 11-308

NASA'S WISE RAISES DOUBT ABOUT ASTEROID FAMILY BELIEVED RESPONSIBLE
FOR DINOSAUR EXTINCTION

WASHINGTON -- Observations from NASA's Wide-field Infrared Survey
Explorer (WISE) mission indicate the family of asteroids some
believed was responsible for the demise of the dinosaurs is not
likely the culprit, keeping the case open on one of Earth's greatest
mysteries.

While scientists are confident a large asteroid crashed into Earth
approximately 65 million years ago, leading to the extinction of
dinosaurs and some other lifeforms on our planet, they do not know
exactly where the asteroid came from or how it made its way to Earth.
A 2007 study using visible-light data from ground-based telescopes
first suggested the remnant of a huge asteroid, known as Baptistina,
as a possible suspect.

According to that theory, Baptistina crashed into another asteroid in
the main belt between Mars and Jupiter about 160 million years ago.
The collision sent shattered pieces as big as mountains flying. One
of those pieces was believed to have impacted Earth, causing the
dinosaurs' extinction.

Since this scenario was first proposed, evidence developed that the
so-called Baptistina family of asteroids was not the responsible
party. With the new infrared observations from WISE, astronomers say
Baptistina may finally be ruled out.

"As a result of the WISE science team's investigation, the demise of
the dinosaurs remains in the cold case files," said Lindley Johnson,
program executive for the Near Earth Object (NEO) Observation Program
at NASA Headquarters in Washington. "The original calculations with
visible light estimated the size and reflectivity of the Baptistina
family members, leading to estimates of their age, but we now know
those estimates were off. With infrared light, WISE was able to get a
more accurate estimate, which throws the timing of the Baptistina
theory into question."

WISE surveyed the entire celestial sky twice in infrared light from
January 2010 to February 2011. The asteroid-hunting portion of the
mission, called NEOWISE, used the data to catalogue more than 157,000
asteroids in the main belt and discovered more than 33,000 new ones.

Visible light reflects off an asteroid. Without knowing how reflective
the surface of the asteroid is, it's hard to accurately establish
size. Infrared observations allow a more accurate size estimate. They
detect infrared light coming from the asteroid itself, which is
related to the body's temperature and size. Once the size is known,
the object's reflectivity can be re-calculated by combining infrared
with visible-light data.

The NEOWISE team measured the reflectivity and the size of about
120,000 asteroids in the main belt, including 1,056 members of the
Baptistina family. The scientists calculated the original parent
Baptistina asteroid actually broke up closer to 80 million years ago,
half as long as originally proposed.

This calculation was possible because the size and reflectivity of the
asteroid family members indicate how much time would have been
required to reach their current locations -- larger asteroids would
not disperse in their orbits as fast as smaller ones. The results
revealed a chunk of the original Baptistina asteroid needed to hit
Earth in less time than previously believed, in just about 15 million
years, to cause the extinction of the dinosaurs.

"This doesn't give the remnants from the collision very much time to
move into a resonance spot, and get flung down to Earth 65 million
years ago," said Amy Mainzer, a study co-author and the principal
investigator of NEOWISE at NASA's Jet Propulsion Laboratory (JPL) in
Pasadena. Calif. "This process is thought to normally take many tens
of millions of years." Resonances are areas in the main belt where
gravity nudges from Jupiter and Saturn can act like a pinball machine
to fling asteroids out of the main belt and into the region near
Earth.

The asteroid family that produced the dinosaur-killing asteroid
remains at large. Evidence that a 10-kilometer asteroid impacted
Earth 65 million years ago includes a huge, crater-shaped structure
in the Gulf of Mexico and rare minerals in the fossil record, which
are common in meteorites but seldom found in Earth's crust. In
addition to the Baptistina results, the NEOWISE study shows various
main belt asteroid families have similar reflective properties. The
team hopes to use NEOWISE data to disentangle families that overlap
and trace their histories.

"We are working on creating an asteroid family tree of sorts," said
Joseph Masiero, the lead author of the study. "We are starting to
refine our picture of how the asteroids in the main belt smashed
together and mixed up."

JPL manages and operated WISE for NASA's Science Mission Directorate.
The spacecraft was put into hibernation mode after it scanned the
entire sky twice, completing its main objectives. The principal
investigator, astronomer Edward Wright, is at UCLA.

The mission was selected competitively under NASA's Explorers Program
managed by the agency's Goddard Space Flight Center in Greenbelt, Md.
The science instrument was built by the Space Dynamics Laboratory in
Logan.

The spacecraft was built by Ball Aerospace & Technologies Corp. in
Boulder, Colo. Science operations and data processing take place at
the Infrared Processing and Analysis Center at the California
Institute of Technology in Pasadena. Caltech manages JPL for NASA.

For more information about WISE, visit:

http://www.nasa.gov/wise

-end-
Received on Mon 19 Sep 2011 02:33:55 PM PDT