Asteroid That Killed the Dinosaurs Was Water-Rich and Traveled Far Before Slamming Into Earth

The asteroid responsible for the mass extinction event that ended the reign of the dinosaurs 66 million years ago did not originate from the more familiar inner regions of our solar system. Instead, new research reveals that this catastrophic asteroid came from the distant reaches of the solar system.

According to a study published Thursday in Science, researchers from Europe and the U.S. have determined that the asteroid responsible for this extinction event formed beyond Jupiter’s orbit, in an extremely cold, water-rich region. This asteroid, unlike most others that have impacted Earth, was rich in both water and carbon.

François Tissot, a professor at the California Institute of Technology and co-author of the study, highlighted that this is the only water-rich asteroid identified from the last 500 million years that struck Earth. “Every other impact was with an object that was nearby the sun that happened to encounter here,” Tissot explained. “So the one that killed the dinosaurs is really special in two ways — by what it did, and also by where it originated.”

This particular asteroid was responsible for creating the Chicxulub crater on Mexico’s Yucatán Peninsula. Although direct samples from the asteroid are unavailable due to its destruction upon impact, researchers were able to analyze dust that fell back to Earth, focusing on fine particles deposited in the Earth’s layers.

A key element in this analysis was ruthenium, which is exceedingly rare on Earth but can be traced back to the asteroid. This study reinforces previous findings that the asteroid was a carbonaceous, or C-type, asteroid and contradicts a 2021 hypothesis suggesting that the impactor might have been a comet.

Tissot noted that while comets, originating from far beyond the sun, are predominantly composed of ice and dust, no comet has been measured for ruthenium. “Based on other indicators from other elements that the community over time has been able to measure, it seems very unlikely to be a comet,” he said.

The research marks a significant step in understanding Earth’s evolutionary history. “If there are enough studies made across the history of the Earth, then suddenly we have a record of all of Earth’s evolution,” Tissot said. “And we can start to ask other questions.”