We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Energetic Proton Losses Reveal Io's Extended and Longitudinally Asymmetrical Atmosphere.
- Authors
Huybrighs, H. L. F.; van Buchem, C. P. A.; Blöcker, A.; Dols, V.; Bowers, C. F.; Jackman, C. M.
- Abstract
Along the I24, I27, and I31 flybys of Io (1999–2001), the Energetic Particle Detector (EPD) onboard the Galileo spacecraft observed localized regions of energetic protons losses (155–1,250 keV). Using back‐tracking particle simulations combined with a prescribed atmospheric distribution and a magnetohydrodynamics (MHD) model of the plasma/atmosphere interaction, we investigate the possible causes of these depletions. We focus on a limited region within two Io radii, which is dominated by Io's SO2 atmosphere. Our results show that charge exchange of protons with the SO2 atmosphere, absorption by the surface and the configuration of the electromagnetic field contribute to the observed proton depletion along the Galileo flybys. In the 155–240 keV energy range, charge exchange is either a major or the dominant loss process, depending on the flyby altitude. In the 540–1,250 keV range, as the charge exchange cross sections are small, the observed decrease of the proton flux is attributed to absorption by the surface and the perturbed electromagnetic fields, which divert the protons away from the detector. From a comparison between the modeled losses and the data we find indications of an extended atmosphere on the day/downstream side of Io, a lack of atmospheric collapse on the night/upstream side as well as a more global extended atmospheric component (>1 Io radius). Our results demonstrate that observations and modeling of proton depletion around the moon constitute an important tool to constrain the electromagnetic field configuration around Io and the radial and longitudinal atmospheric distribution, which is still poorly understood. Plain Language Summary: Io is a moon of Jupiter with active volcanoes and an atmosphere of which the structure and variability is poorly understood. A fascinating object on its own, neutral gas from Io also serves as the main source of plasma in Jupiter's magnetosphere. Improving our understanding of Io's atmosphere will allow us to better understand the precise link between Io's neutral environment and the plasma torus surrounding Jupiter. In this work we analyze data from the historic Galileo spacecraft that encountered Io. Specifically, we analyze regions close to Io where (normally abundant) energetic protons are disappearing. We find that charge exchange between these particles and Io's atmosphere along with the effect of the electric and magnetic fields on the paths of these particles can cause such decreases. Charge exchange with the atmosphere is either a major or the dominant source of losses, depending on the flyby altitude. The losses of the protons are related to Io's atmosphere and hint at an atmosphere that is more extended on Io's day side (also the downstream side from the plasma flow's point of view), doesn't collapse fully on the night (upstream) side, and appears to be more extended than we assumed. Key Points: Atmospheric charge exchange is a major or dominant loss process of energetic protons (155–224 keV) during three close Galileo flybys of IoProton losses suggest an expanded atmosphere on the day/downstream side and a lack of atmospheric collapse on the night/upstream sideDiscrepancies between the data and model hint at a global large scale height atmosphere
- Subjects
GALILEI, Galileo, 1564-1642; CHARGE exchange; PARTICLE detectors; PROTONS; MAGNETIC field effects; PLASMA flow; ATMOSPHERIC nucleation
- Publication
Journal of Geophysical Research. Space Physics, 2024, Vol 129, Issue 7, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2023JA032371