Constraining Europa’s Subsolar Atmosphere With A Joint Analysis Of HST Spectral Images And Galileo Magnetic Field Data

By Keith Cowing
Press Release
August 30, 2022
Filed under , , , , , ,
Constraining Europa’s Subsolar Atmosphere With A Joint Analysis Of HST Spectral Images And Galileo Magnetic Field Data
(a) and (b) Images of the oxygen emission at 1304 ˚A and 1356 ˚A above Europa’s trailing hemisphere for the total O2 + O + H2O atmosphere model, whose individual components are presented in Figure 4. The subsolar point is located at the center of the disk and is indicated with an asterisk. The vertical axis points towards North. (c) and (d) Radial profiles of the average 1304 ˚A and 1356 ˚A brightness within concentric rings from the disk center out to 1.5 RE. The profiles are shown for the total atmosphere and for the individual contributions from O2, O, and H2O.

We constrain Europa’s tenuous atmosphere on the subsolar hemisphere by combining two sets of observations: oxygen emissions at 1304 Å and 1356 Å from Hubble Space Telescope (HST) spectral images, and Galileo magnetic field measurements from its closest encounter, the E12 flyby.

We describe Europa’s atmosphere with three neutral gas species: global molecular (O2) and atomic oxygen (O), and localized water (H2O) present as a near-equatorial plume and as a stable distribution concentrated around the subsolar point on the moon’s trailing hemisphere. Our combined modelling based on the ratio of OI 1356 Å to OI 1304 Å emissions from Roth (2021) and on magnetic field data allows us to derive constraints on the density and location of O2 and H2O in Europa’s atmosphere. We demonstrate that 50% of the O2 and between 50% and 75% of the H2O abundances from Roth (2021) are required to jointly explain the HST and Galileo measurements.

These values are conditioned on a column density of O close to the upper limit of 6×1016 m−2 derived by Roth (2021), and on a strongly confined stable H2O atmosphere around the subsolar point. Our analysis yields column densities of 1.2×1018 m−2 for O2, and 1.5×1019 m−2 to 2.2×1019 m−2 at the subsolar point for H2O. Both column densities however still lie within the uncertainties of Roth (2021). Our results provide additional evidence for the existence of a stable H2O atmosphere at Europa.

Sebastian Cervantes, Joachim Saur

Subjects: Space Physics (; Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2208.13650 [] (or arXiv:2208.13650v1 [] for this version)
Submission history
From: Juan Sebastian Cervantes Villa Dr.
[v1] Mon, 29 Aug 2022 14:52:55 UTC (2,392 KB)
Full paper

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.