Some researchers using isotope signatures from old sediments figured out what type of asteroid impacted the Earth 66 million years ago. The asteroid that wiped out the dinosaurs was likely an exceptionally rare CO chondrite from a distant region of the solar system. Its unusual chemistry suggests that planet-cooling dust and debris, rather than sulfur inside the asteroid, may have delivered the deadliest blow.

A rare type of meteorite known as a CO chondrite was likely the object that slammed into Earth 66 million years ago and triggered the extinction of about 75 percent of all species, including every non-avian dinosaur.

The global clay layer contains only faint traces of the original object, making it difficult to determine exactly what struck Earth. Even so, the nickel isotope signature allowed the researchers to narrow the impactor down to a rare class of carbonaceous meteorite.

https://www.sciencedaily.com/releases/2026/07/260718010142.htm

Apparently, carbonaceous chondrites of the Ornans class are one of the rarest and most primitive type of meteorites, with very little alteration after formation.

CO chondrites, named after the Ornans meteorite that fell in France, are distinctive for their small, well-defined chondrules. They have undergone less alteration than CI and CM chondrites, which makes them valuable for studying early solar system processes.

Water Content: CO chondrites contain little to no water, as they show minimal evidence of aqueous alteration.

Organic Content: While they contain some organic compounds, CO chondrites are less carbon-rich than CI and CM types.

Structure: These meteorites have a compact and dense structure, with abundant chondrules that have remained relatively unaltered since their formation.

Parent Body: The lack of water and limited alteration suggest that CO chondrites formed on a relatively dry and small asteroid that did not undergo significant heating or alteration.

https://www.fossilera.com/pages/carbonaceous-chondrites-a-window-into-the-early-solar-system