Asteroid that doomed the dinosaurs originated beyond Jupiter

The C-type asteroid impact in modern-day Mexico that wiped out the dinosaurs and reshaped the earth's history forever 66 million years ago originated beyond Jupiter, a new study has reported.

It was a turning point in the history of life on the earth. An asteroid an estimated 10-15 km) wide slammed into Mexico’s Yucatan Peninsula 66 million years ago, triggering a global cataclysm that eradicated about three-quarters of the world’s species and ended the age of dinosaurs.

The impact pulverised the asteroid and spread its debris worldwide, still present in a global layer of clay deposited in the aftermath of that fateful day. A new analysis of this debris has resolved a long debate about the nature of the asteroid, showing that it was a type that originated beyond Jupiter in the outer solar system.

The impactor, based on the debris composition, was a carbonaceous asteroid, or C-type, so named because of a high concentration of carbon. The study ruled out that the impactor was a comet or that the debris layer had been laid down by volcanism, as some had hypothesised.

“A projectile originating at the outskirts of the solar system sealed the fate of the dinosaurs,” said geochemist Mario Fischer-Gödde of the University of Cologne in Germany, lead author of the study published on Thursday in the journal Science.

The impact at the end of the Cretaceous Period gouged the Chicxulub (pronounced CHIK-shu-loob) crater, 180 km wide and 20 km deep. The clay layer is rich in metals including iridium, ruthenium, osmium, rhodium, platinum and palladium that are rare on the earth but common in asteroids.

The researchers focused upon ruthenium - specifically, the ratio of its isotopes present in the clay layer. Isotopes are atoms of the same element with slightly different masses because of differing numbers of subatomic particles called neutrons. Ruthenium has seven isotopes, with three especially important in the findings. The ruthenium isotope ratios matched other known carbonaceous asteroids.

“Ruthenium is especially useful in this context as the isotopic signature in the clay layer is almost entirely made up of ruthenium from the impactor and not the background sediment, and ruthenium shows distinct isotopic compositions between inner and outer solar system materials,” said geoscientist and study co-author Steven Goderis of Vrije Universiteit Brussel in Belgium.