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

[Ron Baalke]

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 

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