Collisions between icy comet-like objects out near Pluto are said to be responsible for certain types of otherwise inexplicable cosmic rays that zip through the solar system, according to astronomers.
The frozen Kuiper Belt Objects, leftovers of the solar systems birth, slam together and generate dust that drifts inward, polluting the entire solar system. Charged particles streaming out from the Sun interact with the dust, generating what astronomers call anomalous cosmic rays, according to new research led by scientists at the Southwest Research Institute.
Cosmic rays are the most energetic particles known. Anomalous cosmic rays are so named because they form in the relative vicinity of the Earth, near the sun, and have lower energy than galactic and intergalactic cosmic rays, which form in the far reaches of the galaxy and beyond.
Cosmic rays move throughout the universe at light speed and constantly bombard the Earth.
"This novel finding shows how dust in the cosmos may play an important role for producing the most energetic particles known," says Dr. Nathan Schwadron, a senior research scientist at the institute. "Dust grains are produced in vast amounts through collisions of Kuiper Belt objects. These particles give us a glimpse of the early stages of our solar system when the dust content was much larger, and could parallel other more dusty stellar systems that exist now."
Recent observations of anomalous cosmic rays are puzzling because of the unexpected presence of iron, silicon and carbon. The interstellar medium has lots of carbon, silicon and iron atoms, but electrical charging (ionization) of these elements prevents them from penetrating deeply within the solar system.
"Our team looked for a source already inside the solar system to account for the unusual anomalous cosmic rays -- and we found one in the tiny comet-like grains from the nearby Kuiper Belt," Schwadron said.
As 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.
"This is a big step toward solving the long-standing mystery of the origin of the anomalous component of cosmic rays," said Tom Bogdan, program director in the NSF Division of Atmospheric Sciences, which funded the research.
Cosmic rays are believed to play a role in evolution.
"Cosmic rays are a double-edged sword. They cause genetic mutation and are harmful to living organisms, but on the upside stimulate biological evolution," Schwadron said. "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, and we can now use them to study what's in the Kuiper Belt. Their relationship to the creation or maintenance of life is also worth a closer look."
The new study is detailed in the October 30 issue of Geophysical Research Letters.
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