UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

X-Ray Emission from Jupiter’s Galilean Moons: A Tool for Determining Their Surface Composition and Particle Environment

Nulsen, S; Kraft, R; Germain, G; Dunn, W; Tremblay, G; Beegle, L; Branduardi-Raymont, G; ... Vance, S; + view all (2020) X-Ray Emission from Jupiter’s Galilean Moons: A Tool for Determining Their Surface Composition and Particle Environment. The Astrophysical Journal , 895 (2) p. 79. 10.3847/1538-4357/ab8cbc. Green open access

[thumbnail of Nulsen_2020_ApJ_895_79.pdf]
Preview
Text
Nulsen_2020_ApJ_895_79.pdf - Published Version

Download (1MB) | Preview

Abstract

We analyze archival Chandra X-ray Observatory observations of Jupiter to search for emission from the Galilean moons. X-ray emission has previously been reported from Io and Europa using a subset of these data. We confirm this detection, and marginally detect X-ray emission from both Ganymede and Callisto as well. The X-ray spectrum of Europa is strongly peaked around the neutral oxygen fluorescence line (525 eV), while Io's has peaks at both oxygen and sulfur (2308 eV) plus a broad continuum between 350 and 5000 eV. Ganymede's spectrum is similar to Io's, but without the sulfur peak. A few events, mostly clustered around the oxygen line, are detected from Callisto. Using measurements by the Galileo mission of the specific intensity of ambient protons and electrons, we model the X-ray spectra and flux of the moons from two processes: particle-induced X-ray emission (PIXE) from the impact of energetic protons and X-ray emission from electron bremsstrahlung. With uncertainties of a factor of a few, the electron bremsstrahlung and PIXE models overestimate the X-ray flux from Europa, preventing us from making a definitive statement about the origin of the X-ray emission. The PIXE model of Io predicts emission lines at O and S similar to those observed, but underestimates their flux by nearly two orders of magnitude. Based on this discrepancy in the PIXE flux, combined with the detected broadband continuum in the spectrum, we conclude that the X-ray emission from Io is due to electron bremsstrahlung. Likewise, because of Ganymede's broad continuum, we tentatively conclude that its X-ray emission is also due to electron bremsstrahlung. Callisto is too faint in the X-rays to draw any conclusion. Obtaining in situ X-ray observations of the moons would provide a direct measurement of their elemental composition.

Type: Article
Title: X-Ray Emission from Jupiter’s Galilean Moons: A Tool for Determining Their Surface Composition and Particle Environment
Open access status: An open access version is available from UCL Discovery
DOI: 10.3847/1538-4357/ab8cbc
Publisher version: http://dx.doi.org/10.3847/1538-4357/ab8cbc
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10100070
Downloads since deposit
77Downloads
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item