Cutoff Rigidities, Galactic Cosmic Ray Flux, and Heavy Ion Detections at Jupiter

Abstract

AbstractA map of vertical cutoff rigidities has been calculated for galactic cosmic ray (GCR) entry into the atmosphere of Jupiter at the 1 bar pressure radius (1 RJ = 71,492 km) using the JRM33 comprehensive model of Jupiter's magnetic field (based on 32 close flybys of Jupiter by the Juno satellite) along with a particle trajectory code (Geomagnetic Cutoff Rigidity Computer Program). The map was combined with measurements of the GCR proton flux at Earth, from the BESS‐Polar ii campaign, to calculate a corresponding proton flux map at Jupiter. Additional cutoff rigidity maps were calculated for 1,000 km above the 1 bar level, and for 1.41 RJ. Furthermore, detections of heavy particles from Juno's Stellar Reference Unit were analyzed for their cutoff rigidities in multiple directions. Cutoff rigidities of 3.5–7.5 GV were found for five of the detections furthest out making them possible GCR candidates. The majority of points, located below 1.6 RJ are not likely to be GCR. Assuming instead that they are trapped particles we have calculated upper and lower limits on their equatorial pitch angles, resulting in a range from 10.1° to 27.1°, which can help constraining Jupiter's energetic radiation.