A team of scientists has detected sudden bursts of cosmic rays around the Voyagers. The bursts, they report, are caused by shock waves emanating from solar eruptions that spew particles out at a million miles an hour. The shock waves take more than a year to reach the Voyagers, but when they do, they excite cosmic-ray electrons nearby. Scientists have observed similar phenomena closer to home, around Earth and our planetary neighbors, but never in interstellar space.

“We’re really discovering that what we thought would be this quiet, pristine interstellar medium is actually disturbed considerably” by the sun, Don Gurnett, a University of Iowa professor emeritus of physics and astronomy, who led the research.