NASA’s Juno Reveals New Insights into Cosmic Ray Origins

Particles traveling close to the speed of light near Jupiter were captured by NASA’s Juno mission, providing new evidence for how and where high-energy particles, including cosmic rays, form.

Astronomers have sought the origins of cosmic rays since their discovery more than 100 years ago. These energetic particles can come from many sources, including supernovas and eruptions from the Sun. When solar cosmic rays — commonly called solar energetic particles — reach Earth, they can trigger space weather effects that disrupt satellites, communications, and power systems.

NASA missions like MMS (Magnetospheric Multiscale) and THEMIS (Time History of Events and Macroscale Interactions during Substorms) showed how some electrons become highly energized in a region near Earth called the foreshock, where solar particles first encounter Earth’s magnetic field. Scientists suspected the same process was responsible for accelerating high-energy particles in foreshocks at other planets and astrophysical systems, but they could not confirm it until now.

New observations around Jupiter provide direct confirmation of this process. While orbiting the gas giant, Juno measured high-speed electrons in Jupiter’s foreshock region. These electrons reached even higher speeds than Earth’s, scaling with the giant planet’s larger-sized bow shock, formed when Jupiter’s magnetic field pushes through the stream of solar particles.

The results were published Wednesday in the journal Nature.

The scientists also found that this scaling relationship matched cosmic rays seen coming from supernovas across the galaxy, where even larger magnetic environments create even faster particles. This suggests the same process occurring within the solar system can occur across the universe.

By Mara Johnson-Groh
NASA’s Goddard Space Flight Center, Greenbelt, Md.