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Europa’s neutral gas torus: Observational constraints from HST/COS

Presentation #314.07 in the session Icy Satellites, Fields and Particles (Poster + Lightning Talk)

Published onOct 23, 2023
Europa’s neutral gas torus: Observational constraints from HST/COS

We searched for faint ultraviolet emissions from a neutral gas torus near the orbit of Jupiter’s moon Europa, using the Cosmic Origins Spectrograph of the Hubble Space Telescope (HST/COS). The existence of enhanced neutrals near Europa’s orbit is indirectly supported by in situ plasma measurements and some remote sensing results. Simulations suggest that a torus consisting primarily of molecular hydrogen can be sustained by escape from Europa’s atmosphere. However, the neutral torus has not yet been observed more directly. We present HST/COS observations from 2020 and 2021, scanned along the equatorial plane of the Jupiter system near Europa’s projected orbital distance. Our search yields no detectable emissions, only upper limits, from the inferred torus’s primary neutral gasses (H2, H, O, and O2). We compare these limits to brightnesses simulated in a neutral torus model. The new observational constraints are consistent with expectations from recent simulations: a neutral torus that is dilute and primarily consists of molecular hydrogen. Sulfur ion emissions detected radially interior to Europa’s orbit are consistent with the extended Io plasma torus.

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