Cosmic rays and where they come from are one of the greatest mysteries of astronomy. To greatly oversimplify, cosmic rays are the centers or nuclei of atoms that have had all the surrounding electrons stripped off and have then been accelerated to extremely high levels of energy. The lighter (and less damaging) cosmic rays are thought to come mainly from supernovas around the galaxy; the heavier and super-energetic ones are the most mysterious. Why do we care? Because an astronaut on a trip to and from Mars would receive most of her trip space radiation dose from cosmic rays that are simply too energetic to shield. It’s not just her fertility at risk; cosmic rays are believed to play a role in evolution on Earth, too. “Cosmic rays are a double-edged sword. They cause genetic mutation and are harmful to living organisms, but on the upside stimulate biological evolution,” says researcher Dr. Nathan Schwadron. “Cosmic rays are our only available sample of matter from the far reaches of the distant galaxy, and from other galaxies. They can tell us a lot about what’s in the universe.”
Dr. Schwadron’s latest work suggests heavy cosmic rays come not from the depths of interstellar or intergalactic space, but from comets hitting dust grains just out beyond the orbit of Pluto. According to his recent paper in Geophysical Research Letters, the grains produced by collisions in the Kuiper Belt drift in toward the Sun, they are bombarded by solar wind particles, which causes sputtering and frees the carbon, silicon and iron atoms from within, the thinking goes. Those particles interact with solar radiation, transforming them into ions, or charged particles. The solar wind then sweeps them out and accelerates them to anomalous cosmic ray energies at the edge of the solar system, where they are bounced to and fro by magnetic fields in the solar wind and in the medium beyond the solar system, Schwadron said. Pehaps the ancient belief that comets directly influence our fate on Earth has some merit after all.