Upper limits for X ‐ ray and energetic neutral particle emission from Jupiter: Voyager‐1 results

Abstract

The x‐ray sensitivity of the low energy proton channels in the Low Energy Charged Particle (LECP) experiment and its directional measurements are used to determine whether x‐rays from Jupiter can be recognized as additional flux above background as Voyager 1 approached the planet. Between ∼230 and ∼100 RJ a statistically significant count rate was detected which we interpret as x‐rays and/or neutral particles. The upper limit for x‐rays, related to earth‐based measurements is ≤ 1.3 × 10−4 photons/cm² sec keV in the energy range 14 to 31 keV. Such an x‐ray flux leads to estimates of precipitating electrons over the Jovian polar caps which are 200 times larger than over observed electron fluxes in the Io plasma torus. The same upper limit corresponds to ≤ 4 × 10−2 neutral particles/cm² sec keV at 100 RJ distance from Jupiter. We favor the neutral hypothesis, and estimate that it represents a loss of ≤ 1025 atoms/sec, i.e. < 0.05% of the atoms generated by Io’s volcanoes.