From the dinosaurs' perspective, not much has changed. Scientists still think an enormous chunk of rock slammed into Earth and triggered a cataclysmic explosion that wiped them out. However, a new study out of Harvard changes the theory about the origins of that space rock, reports NPR. The researchers say the "impactor" wasn't from a mammoth asteroid that originated from relatively nearby—somewhere between Mars and Jupiter—but instead from a smaller comet that hailed from much further away, specifically a region known as the Oort cloud at the edge of the solar system, per the Harvard Gazette. Under this theory, the comet was whizzing along when it got knocked off course by Jupiter's gravity and sent near the sun, whose forces caused the comet to fragment. One of those fragments, about the size of Boston, hit off the coast of Mexico and caused what has come to be known as the Chicxulub crater.
“Basically, Jupiter acts as a kind of pinball machine,” says Harvard's Amir Siraj. “Jupiter kicks these incoming long-period comets into orbits that bring them very close to the sun.” Their study suggests these so-called "sun grazers" are far more common than thought and can explain other craters on Earth. As part of their evidence, they say that craters such as Chicxulub were hit by impactors made of a rocky material called carbonaceous chondrite, which is more common in long-range comets than in asteroids. Debate settled? Not even close. “I believe their work has several intrinsic problems that work against their hypothesis,” Bill Bottke, a planetary scientist at the Southwest Research Institute in Colorado, tells the New York Times. Another skeptical scientist tells the newspaper that cometary fragments would be too small to cause the devastation of 66 million years ago. (Read about a very special dinosaur butt.)