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Observation and origin of non-thermal hard X-rays from Jupiter

Mori, Kaya and Hailey, Charles and Bridges, Gabriel and Mandel, Shifra and Garvin, Amani and Grefenstette, Brian and Dunn, William and Hord, Benjamin J. and Branduardi-Raymont, Graziella and Clarke, John and Jackman, Caitriona and Nynka, Melania and Ray, Licia (2022) Observation and origin of non-thermal hard X-rays from Jupiter. Nature Astronomy, 6 (4). pp. 442-448. ISSN 2397-3366. doi:10.1038/s41550-021-01594-8.

[img] Image (JPEG) (Extended Data Fig. 1: Magnetic Footprint of Juno for the 12th Peri-jove) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 2: Altitude Distribution of Escaping X-Rays) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 1: NuSTAR observations of Jupiter) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 2: Juno orbits coincident with NuSTAR observations and electron spectral parameters) - Supplemental Material
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Electrons accelerated on Earth by a rich variety of wave-scattering or stochastic processes generate hard, non-thermal X-ray bremsstrahlung up to ~1 MeV (refs. 3,4) and power Earth’s various types of aurorae. Although Jupiter’s magnetic field is an order of magnitude larger than Earth’s, space-based telescopes have previously detected X-rays only up to ~7 keV (ref. 5). On the basis of theoretical models of the Jovian auroral X-ray production, X-ray emission in the ~2–7 keV band has been interpreted as thermal (arising from electrons characterized by a Maxwell–Boltzmann distribution) bremsstrahlung. Here we report the observation of hard X-rays in the 8–20 keV band from the Jovian aurorae, obtained with the NuSTAR X-ray observatory. The X-rays fit to a flat power-law model with slope of 0.60 ± 0.22—a spectral signature of non-thermal, hard X-ray bremsstrahlung. We determine the electron flux and spectral shape in the kiloelectronvolt to megaelectronvolt energy range using coeval in situ measurements taken by the Juno spacecraft’s JADE and JEDI instruments. Jovian electron spectra of the form we observe have previously been interpreted as arising in stochastic acceleration, rather than coherent acceleration by electric fields. We reproduce the X-ray spectral shape and approximate flux observed by NuSTAR, and explain the non-detection of hard X-rays by Ulysses, by simulating the non-thermal population of electrons undergoing precipitating electron energy loss, secondary electron generation and bremsstrahlung emission in a model Jovian atmosphere. The results highlight the similarities between the processes generating hard X-ray aurorae on Earth and Jupiter, which may be occurring on Saturn, too.

Item Type:Article
Related URLs:
URLURL TypeDescription ReadCube access ItemNASA HEASARC website ItemPlanetary Data System ItemLASP MOP group website ItemCode Correction Correction - Free ReadCube access
Mori, Kaya0000-0002-9709-5389
Hailey, Charles0000-0002-3681-145X
Mandel, Shifra0000-0002-6126-7409
Grefenstette, Brian0000-0002-1984-2932
Dunn, William0000-0002-0383-6917
Hord, Benjamin J.0000-0001-5084-4269
Branduardi-Raymont, Graziella0000-0002-6620-6357
Jackman, Caitriona0000-0003-0635-7361
Nynka, Melania0000-0002-3310-1946
Ray, Licia0000-0003-3727-602X
Additional Information:© 2022 Nature Publishing Group. Received 17 February 2021; Accepted 16 December 2021; Published 10 February 2022. We thank R. Wilson for his help in analysing JADE data. We also thank the MOP group of LASP for their work on Juno’s trajectory and magnetic footprint. We acknowledge D. Wik for his help in analysing NuSTAR background data. Support for this work by K.M. was provided by NASA through NuSTAR Cycle 3 Guest Observer Program grant number NNH16ZDA001N. Support for this work by C.J. at DIAS was supported by the Science Foundation Ireland grant number 18/FRL/6199. Data availability: The NuSTAR and XMM-Newton data are archived at NASA’s HEASARC website ( The JEDI, JADE and MAG data are available at the Planetary Data System( The magnetic footprint of JUNO is available through the LASP MOP group’s website ( Code availability: NuSTAR and XMM-Newton data were analysed by HEASOFT version 6.28 and SAS analysis software version 16.1.0, respectively. GEANT4 is publicly available at The simulation and data reduction code is available from the corresponding author upon request. Contributions: K.M., C.H., G.B. and S.M. wrote the manuscript and made large contributions to data analysis and interpretation. G.B. performed the JADE/JEDI data analysis and GEANT4 simulations. S.M. and B.J.H. analysed NuSTAR data. B.G. contributed to NuSTAR data analysis and interpretation. A.G. and W.D. were involved with XMM-Newton data analysis. J.C. and M.N. conducted a feasibility study of NuSTAR observations of Jupiter. G.B.-R., C.J. and L.R. interpreted the analysis results and provided insights into Jovian aurora physics. All authors contributed to discussing the results and commented on the manuscript. The authors declare no competing interests. Peer review information: Nature Astronomy thanks Tomoki Kimura and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Errata:Mori, K., Hailey, C., Bridges, G. et al. Publisher Correction: Observation and origin of non-thermal hard X-rays from Jupiter. Nat Astron (2022).
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Science Foundation, Ireland18/FRL/6199
Subject Keywords:Giant planets; High-energy astrophysics
Issue or Number:4
Record Number:CaltechAUTHORS:20220303-310356500
Persistent URL:
Official Citation:Mori, K., Hailey, C., Bridges, G. et al. Observation and origin of non-thermal hard X-rays from Jupiter. Nat Astron 6, 442–448 (2022).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113708
Deposited By: Tony Diaz
Deposited On:03 Mar 2022 18:10
Last Modified:25 Apr 2022 20:34

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