Dark matter seems to hold galaxies snugly together across the universe—but it could also hurl comets at Earth and threaten our entire species, according to a new study. This is based on a theory that there's a huge disk of dark matter lying on the central plane of the Milky Way, and our sun travels through it when orbiting the middle of the galaxy. Now, Harvard physicists say the disk may disturb comets in our outer solar system and redirect them toward Earth, Space.com reports. This could also explain why comets bombard Earth on a roughly 35-million-year cycle.
On that front, Harvard physicists looked at big Earth craters over the past 250 million years, and found a close (but not perfect) match to the timing of the sun's pass through the Milky Way's central plane. That nearly coincides with the extinction of the dinosaurs 67 million years ago, too—but the timing isn't dead-on. Another problem: Dark matter likely consists of weakly interacting massive particles (WIMPs) that create a halo around the Milky Way, not a disk; to make a disk, some dark matter must have strong electromagnetic-like interactions, Physics reports. So the dark matter/comet theory may be "a remote possibility," says one of the study's authors, but "it's still incredibly interesting." (More dark matter stories.)