![]() ![]() What type of object slammed into Earth that fateful day 66 million years ago? Alvarez and his team suspected it was an asteroid, and that remains the general consensus. It's not unanimous, however some researchers think a comet blasted out Chicxulub Crater. In a February 2021 paper, for example, Harvard astrophysicists Amir Siraj and Avi Loeb argued that comets are the best match with the geochemical evidence, which indicates that the impactor had a carbonaceous chondrite composition. (Carbonaceous chondrites are a relatively rare type of dark, primitive meteorite containing high levels of carbon and minerals that were altered by water, among other characteristics.) Siraj and Loeb also calculated that about one-fifth of all long-period comets - icy wanderers that take more than 200 years to complete one orbit - break apart when they pass close to the sun, generating lots of fragments. "This population could increase the impact rate of long-period comets capable of producing Chicxulub impact events by an order of magnitude," Siraj and Loeb wrote in the study, which was published in the journal Scientific Reports. "This new rate would be consistent with the age of the Chicxulub impact crater, thereby providing a satisfactory explanation for the origin of the impactor."
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