Dinosaurs fascinate everyone: they're big, they're scary, and we're not entirely sure what exactly happened to them. We know that large meteorite impacts hit Earth at the time, resulting in mass extinctions, but what caused these impacts? Now, two theoretical physicists propose an answer: dark matter.
It’s no question that meteorites often hit Earth: it’s happened recently. Larger impacts tend to happen on a cyclical basis, 35 million years apart. Theoretical physicists Lisa Randall and Matthew Reece of Harvard University propose that a layer of dark matter at the heart of our galaxy could be to blame. As our solar system orbits the center of the Milky Way, it dips up and down a little bit, occasionally crossing this disk of dark matter. When this happens, the dark matter creates an extra push of gravity on the comets and asteroids that live outside of our solar system in the distant Oort cloud. These comets react, break up, and head towards Earth in massive waves — and when they hit, they can wipe out entire species, like the dinosaurs.
This theory is unique in that previous models couldn’t figure out a force strong enough to cause these massive meteorite impacts. Randall and Reece’s theory, however, accounts for that with the disk of dark matter. There is one problem with their idea, though: dark matter is too weak to have this much of a gravitational effect. However, Randall and Reece suggest that a different kind of dark matter, “dissipative dark matter,” is at play here, thanks to some odd signals, attributed to dark matter, observed by the Fermi Gamma-ray Space Telescope recently. This kind of dark matter is denser and more powerful and could be attributed to creating the massive meteor showers that could damage Earth enough to create mass extinctions.
But how do these two physicists prove this? The idea of a regular cycle of the Sun passing through the dark matter disk itself is questionable. Using models, they compared their data to information we have about large craters here on Earth. Their final numbers made the theory seem slightly more likely than a random meteorite strike being the cause of the dinosaurs' disappearance. Unfortunately, this still doesn’t prove that a disk of dark matter exists in our Galaxy. We may know more after the ESA’s Gaia mission, which is mapping out the Galaxy’s gravitational field, starts sending us data later this year.