The path our Solar System takes through the Galaxy may get bumpy at times, and this could affect the number of comets buzzing around Earth. Scientists have uncovered possible evidence of this galactic bumpiness in an apparent periodic fluctuation in the rate of large crater-forming impacts—the kind that likely killed off the dinosaurs. The frequency of impact fluctuations closely matches the rate at which the Sun passes through the plane of the galactic disk. However, it hasn’t been clear what element in the disk could be influencing comet trajectories. Two theoretical physicists have put forward a hypothesis that inserts dark matter as the missing piece between Solar System motion and possibly life-threatening comet impacts. In a paper published in Physical Review Letters , Lisa Randall and Matthew Reece from Harvard University suggest that some of the mysterious invisible matter, which makes up
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