The Chicxulub Impactor: Comet or Asteroid?

Steve Desch, Alan Jackson, Jessica Noviello, Ariel Anbar

To be published in Astronomy and Geophysics


“A recent paper by Siraj & Loeb (2021) entitled “Breakup of a long-period comet as the origin of the dinosaur extinction ” attempts to revive the perennial debate about what type of body hit the Earth 66 million years ago, triggering the end-Cretaceous extinction. Here we critique the paper and assess the evidence it presents. To consider a comet more likely than an asteroid requires extreme assumptions about how comets fragment, conflation of carbonaceous chondrites with specific types of carbonaceous chondrites, and a blind eye to the evidence of the iridium layer. “

Reply to Desch et al. (PDF)
Amir Siraj, Abraham Loeb

“We reply to criticisms by Desch et al. (2021) regarding our Scientific Reports paper, Breakup of a long-period comet as the origin of the dinosaur extinction. The background impact rates of main-belt asteroids and long-period comets have been previously dismissed as being too low to explain the Chicxulub impact event. Our work demonstrates that a fraction of long-period comets are tidally disrupted after passing close to the Sun, each producing a collection of smaller fragments that cross the orbit of Earth. This population could increase the impact rate of long-period comets capable of producing Chicxulub impact events by an order of magnitude. This new rate would be consistent with the age of the Chicxulub impact crater. Our results are subject to an uncertainty in the number of fragments produced in the breakup event. “