Asteroid That Ended the Dinosaurs Came From Beyond Jupiter, Study Finds

Sixty-six million years ago, an enormous asteroid collided with Earth, contributing to a mass extinction event that wiped out all the non-avian dinosaurs. Now, scientists suggest they’ve tracked down the origin of this celestial agent of destruction.

An analysis of metal isotopes scattered from the impact suggests the asteroid traveled from the outer solar system, beyond Jupiter, researchers report Thursday in the journal Science. The authors also looked at five other asteroid impacts and found they were created by space rocks that formed in the inner solar system.

“I find these results very convincing,” Steve Desch, an astrophysicist at Arizona State University, who did not contribute to the findings, tells Scientific American’s Lee Billings. “They dovetail nicely with lots of other evidence.”

“The paper presents a fantastic set of isotope analyses,” David Kring, a scientist at the Lunar and Planetary Institute who originally linked the impact crater to the mass extinction event and was not involved in the new research, says to Live Science’s Sharmila Kuthunur. “You need to understand the origin of objects like this if you’re going to properly assess future hazards.”

Earth has experienced five mass extinctions in its history, including one around 250 million years ago called the “Great Dying,” when all but about 5 percent of life on Earth went extinct. The most recent event is the one that wiped out the dinosaurs.

The asteroid at fault, known as the Chicxulub impactor, is thought to have been between 6 and 12 miles wide—but due to its high velocity, it formed a crater more than 90 miles across. It was traveling at a speed of 15.5 miles per second and had power equal to 10,000 times the world’s nuclear arsenal, according to NASA. It struck the Earth on the Yucatán Peninsula in present-day Mexico, at what is now called the Chicxulub crater.

After the asteroid hit, around 80 percent of all animal species went extinct. The impact would have shot unfathomable quantities of soot and vapor into the atmosphere, shrouding the world below and triggering a widespread die-off.

“This impact totally changed the picture of our planet and caused the emergence of mammalian life,” Mario Fischer-Gödde, lead author of the new study and a geochemist at the University of Cologne in Germany, tells Scientific American.

Additionally, the impact released metals that settled onto the ground across the planet and are now preserved in a layer of rock that marks when the impact took place. Situated between the Cretaceous and Paleogene eras in the geologic record, it is known as the K/Pg boundary.

One of these metals is ruthenium, which is rare on Earth but common in meteorites, according to a statement. The relative amount of ruthenium isotopes in an asteroid depends on where it comes from in space, according to Science News’ Carolyn Gramling. So, the team examined levels of ruthenium’s seven isotopes at the K/Pg boundary to find the “signature” for where the Chicxulub asteroid originated.

“The idea for this study was born on the rationale that if different types of meteorites can be distinguished according to their ruthenium isotope compositions, and if the enrichment of elements such as ruthenium in the boundary layer is of extraterrestrial origin, the ruthenium isotope data from the boundary layer samples would provide information on the type of impactor,” Fischer-Gödde tells National Geographic’s Riley Black.

Scientists took samples from various sites at the K/Pg boundary, as well as five other impact locations. They found that the boundary samples had ruthenium isotope signatures similar to carbon-rich meteorites that form in the outer solar system, suggesting the infamous asteroid came from out there as well. The other impact sites were more consistent with asteroids from the inner solar system, which have more silicate minerals.

The paper’s “interpretation is not new,” Richard J. Walker, a geochemist at the University of Maryland who did not contribute to the findings, tells Scientific American. “But this study presents a much more ironclad determination that the Chicxulub impactor was a carbonaceous asteroid.”

It also suggests the impactor was not a comet, as some researchers had previously hypothesized. The study supports prior evidence that the strike was indeed caused by an asteroid and “does a really good job of kind of nailing that home,” Sean Gulick, a geophysicist at the University of Texas at Austin who was not involved in the work, says to Nature News’ Michael Marshall.

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.