Dinosaur-killing asteroid identified as rare ‘oddball’ meteorite

The asteroid that wiped out the dinosaurs 66 million years ago has been identified as a CO chondrite — one of the rarest and most primitive classes of space rock known to science. The finding, published July 17 in Science Advances, narrows the hunt for the impactor's origins to the distant outer Solar System or the outer asteroid belt near Jupiter.eurekalert+1

Nickel Isotopes Crack the Case

Researchers from the Institut de Physique du Globe de Paris, Université de Paris, Vrije Universiteit Brussel, the University of British Columbia, and the University of Vienna used high-precision nickel isotope measurements to analyze a thin layer of clay deposited around the globe when the Chicxulub impactor vaporized on contact with Earth's surface. Only a minute fraction of the original projectile survives in that clay, making the analysis exceptionally difficult.ipgp+1

"Carbonaceous chondrites of the Ornans class are definitely not like the typical meteors you find in museum collections," said Dr. Philippe Claeys, a professor with Vrije Universiteit Brussel who worked on the study as a visiting professor at UBC. "A CO contains much less volatile elements — like carbon, zinc, water and particularly sulphur — than other classes of meteorites we've discovered so far on Earth."eurekalert

The isotopic signatures ruled out several previously suspected meteorite types and aligned most closely with CO chondrites, or possibly a closely related proposed class called CT chondrites.zmescience+1

A Cosmically Unlucky Strike

CO chondrites are among the most primitive and unaltered materials in the Solar System. Carbonaceous chondrites as a whole make up only about five percent of meteorites sampled on Earth, and the Ornans subclass represents a tiny fraction of even that small group.eurekalert

The finding builds on a 2024 study in Science that used ruthenium isotopes to establish the Chicxulub impactor was a carbonaceous-type asteroid formed beyond the orbit of Jupiter. The new nickel isotope data provides a more specific classification within that broad category.science+1

Because CO chondrites contain relatively little sulfur, the results suggest the impactor itself contributed fewer climate-altering sulfur gases to the atmosphere than some models had assumed. Instead, fine debris lofted into the atmosphere was likely the primary driver of the extinction.zmescience+1

An Unlucky Extinction

The Cretaceous-Paleogene impactor was roughly 10 to 15 kilometers wide and struck at an estimated 64,000 km/h, forming the Chicxulub crater now buried beneath Mexico's Yucatán Peninsula.eurekalert

"Being impacted by such a rare, distant projectile really underscores how unlucky the dinosaurs were," said Claeys.eurekalert