The asteroid widely believed to be responsible for the demise of the dinosaurs probably couldn't have been, observations from NASA's Wide-field Infrared Survey Explorer (WISE) telescope show.
Scientists are now pretty confident that a large asteroid crashed into Earth around 65 million years ago, leading to the extinction of dinosaurs and other lifeforms.
And a 2007 study using visible-light data from ground-based telescopes first tipped the remnant of a huge asteroid known as Baptistina, as a possible suspect.
Baptistina, ther theory goes, crashed into another asteroid in the main belt between Mars and Jupiter about 160 million years ago. One of the resulting fragments was believed to have hit Earth.
However, evidence has since been found that the Baptistina family of asteroids wasn't responsible - and, with the new WISE observations, astronomers say that theory can 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," says Lindley Johnson, program executive for the Near Earth Object (NEO) Observation Program.
"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."
The size and reflectivity of asteroid family members can be used to work out how much time would have been required to reach their current locations, with larger asteroids dispersing in their orbits more slowly than smaller ones.
The NEOWISE team measured the reflectivity and size of about 120,000 asteroids in the main belt, including 1,056 members of the Baptistina family, and calculated that the original parent Baptistina asteroid actually broke up closer to 80 million years ago, half as long as originally proposed.
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," says Amy Mainzer, principal investigator of NEOWISE.
"This process is thought to normally take many tens of millions of years."
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," says 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."