Around 65 million years ago, an asteroid plummeted to Earth, triggering a cascade of events that led to the demise of the dinosaurs, among other life forms.

The guilty party, previous studies showed, hailed from a family of asteroids called the Baptistina, residents of the main asteroid belt between Mars and Jupiter. One of their members, the story goes, crashed into a sizeable neighbor some 160 million years ago, and shattered, sending at least one hefty chunk hurling toward Earth.


Or maybe not.

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New evidence from NASA's Wide-Field Infrared Survey Explorer, or WISE telescope, exonerates the Baptistina family, scientists repotted Monday.

New data refined the age estimates of the suspect's family, casting doubt they were around at the right time to cause the impact.

Rather, the original parent Baptistina asteroid seems to have broken apart closer to 80 million years ago, about half as long as originally proposed, which doesn't give any large pieces enough time to have reached Earth to trigger the dinosaur-killing impact, says astronomer Amy Mainzer, with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The WISE team reached its conclusion after surveying more than 157,000 asteroids, including 1,056 members of the Baptistina family.

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The asteroid family that produced the killer rock remains at large. Scientists are reconstructing positioning data in search of an asteroid about 6.2 miles (10 kilometers) in diameter that smashed into Earth, leaving a massive crater-shaped impact basin in the Gulf of Mexico and meteorite-type minerals in the fossil records.

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

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Image: Artist's rendering of asteroid smash-up. Credit: NASA/JPL-Caltech