Long-period, high-inclination comets of the sort that can cause extinction-level impacts here on Earth have long been thought to originate from a theoretical Oort cloud. That is, a roughly spherical cloud of icy cometary objects that number in the trillions at distances that extend up to 1.6 light-years away.
More recently, Richard Muller, a well-known professor emeritus of physics at the University of California, Berkeley, put forth the idea that long-period comets that visit our inner solar system are not just perturbed by passing stars at the outer edges of the Oort cloud. But they are also perturbed by a low-mass red dwarf star (dubbed Nemesis) that, along with our sun, is orbiting around a common center of gravity.
Due to Nemesis' slightly eccentric oval orbit around the Oort cloud, it periodically perturbs billions of comets that surround our outer solar system.
Every time Nemesis gets closest to the Oort cloud is when the comets kick in, and this comet shower lasts for maybe a million years, Muller told me via phone. That's when Nemesis is in the densest part of the comet cloud, and that's when the number of deflected Oort cloud comets into the inner solar system is at a maximum, he says.
Just to be clear, this is not any sort of Planet X. This also doesn't have anything to do with random stellar interlopers that sometimes pass close enough to perturb our Oort cloud and stir up a plethora of inward-bound comets.
In contrast, there is nothing random about Nemesis. This is a phenomenon with a clear periodicity. According to Muller, it's responsible for 250 million years of clearly defined periodic Earth impacts.
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