Harvard researchers have a new theory on what killed the dinosaurs

Scientists know that about 66 million years ago, a major event happened on earth that resulted in the extinction of the dinosaurs. The Chicxulub impactor, as the impact is known, left behind a massive crater off the coast of Mexico 93 miles wide and 12 miles deep. While scientists know this is the impact that made many species on Earth at the time go extinct, there is debate about exactly what the Chicxulub impactor was and where it came from.

The puzzle is where did the asteroid or comet originate from and why did it strike the Earth. A new study published by Harvard University astrophysics undergraduate student Amir Siraj and astronomer Avi Loeb could explain the origins and the journey of the object before it impacted the earth. The researchers used statistical analysis and gravitational simulations to calculate that a significant fraction of long-period comets originating from the Oort cloud can be knocked off course by Jupiter's gravitational field during their orbit.

Comets known as sungrazers can be put under powerful tidal forces able to break apart pieces of rock and produce cometary shrapnel during their close passage by the sun. During a close pass to the sun, the portion of the comet closer to the sun is impacted by stronger gravitational pull than the part further away from the sun resulting in tidal force across the object. This can lead to a tidal disruption event where a large comet breaks into many smaller pieces.

One crucial part of this event is that there's a greater chance that one of the fragments will hit the earth on the journey back to the orc cloud. New calculations from the researchers show that the chances of long-period comets impacting the Earth are increased by a factor of about ten and that about 20 percent of long-period comets become sungrazers.

The new rate of impact is consistent with the age of Chicxulub and gives a satisfactory explanation for its origin and other impactors like it. Evidence found in the Chicxulub crater suggests the rock was composed of carbonaceous chondrite, which is widespread among long-period comets but rare among asteroids.