Origin of dinosaur-killing asteroid remains a mystery

NASA’s WISE mission rules out the Baptistina family of asteroids in the search for which asteroid killed the dinosaurs.

Observations from NASA’s Wide-field Infrared Survey Explorer (WISE) mission indicate the family of asteroids some believed responsible for the demise of the dinosaurs is not likely the culprit, keeping open the case on one of Earth’s greatest mysteries. NASA made the announcement on September 19, 2011.

While scientists are confident a large asteroid crashed into Earth approximately 65 million years ago, leading to the extinction of dinosaurs and some other life forms 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.

Artist’s illustration of a broken-up asteroid. Scientists think that a giant asteroid, which broke up long ago in the main asteroid belt between Mars and Jupiter, eventually made its way to Earth and led to the extinction of the dinosaurs. Data from NASA’s WISE mission likely rules out the leading suspect, a member of a family of asteroids called Baptistina, so the search goes on. Image Credit: NASA/JPL-Caltech

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

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

Lindley Johnson, of the Near Earth Object (NEO) Observation Program at NASA, said:

As a result of the WISE science team’s investigation, the demise of the dinosaurs remains in the cold case files. 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, but 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.

Tyrannosaurus rex and Triceratops were two dinosaurs that lived at the time an asteroid hit Earth. Image Credit: Charles R. Knight

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 that the original parent Baptistina asteroid actually broke up closer to 80 million years ago, half as long as originally proposed.

Amy Mainzer, principal investigator of NEOWISE at NASA’s Jet Propulsion Laboratory (JPL), said:

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. 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 (about 6.2-mile) 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.

Bottom line: Findings from NASA’s Wide-field Infrared Survey Explorer (WISE) mission have eliminated the Baptistina family of asteroids as being responsible for the demise of the dinosaurs, according to a NASA press release on September 19, 2011.

Read more at NASA

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