Jupiter as a Giant Cosmic Ray Detector

TL;DR

This paper proposes using Jupiter's atmosphere as a giant detector for ultra-high-energy cosmic rays, suggesting that space observatories like Fermi-LAT and ALMA could detect and analyze these rare events to study cosmic ray fluxes.

Contribution

It introduces a novel method of detecting ultra-high-energy cosmic rays by leveraging Jupiter's large atmosphere and predicts detection capabilities of current space observatories.

Findings

Jupiter's atmosphere acts as an effective cosmic ray detector of 3.3×10^7 km^2.

Fermi-LAT can detect cosmic rays >10^21 eV at about one event per month.

Simultaneous Fermi-LAT and ALMA observations can constrain cosmic ray energies.

Abstract

We explore the feasibility of using the atmosphere of Jupiter to detect Ultra-High-Energy Cosmic Rays (UHECR's). The large surface area of Jupiter allows us to probe cosmic rays of higher energies than previously accessible. Cosmic ray extensive air showers in Jupiter's atmosphere could in principle be detected by the Large Area Telescope (LAT) on the Fermi observatory. In order to be observed, these air showers would need to be oriented toward the Earth, and would need to occur sufficiently high in the atmosphere that the gamma rays can penetrate. We demonstrate that, under these assumptions, Jupiter provides an effective cosmic ray "detector" area of $3.3 \times 10^7$ km$^2$. We predict that Fermi-LAT should be able to detect events of energy $>10^{21}$ eV with fluence $10^{-7}$ erg cm$^{-2}$ at a rate of about one per month. The observed number of air showers may provide an indirect measure of the flux of cosmic rays $\gtrsim 10^{20}$ eV. Extensive air showers also produce a synchrotron signature that may be measurable by ALMA. Simultaneous observations of Jupiter with ALMA and Fermi-LAT could be used to provide broad constraints on the energies of the initiating cosmic rays.