A brightening of Jupiter’s auroral 7.8-μm CH4 emission during a solar-wind compression
journal contributionposted on 2019-04-30, 14:40 authored by JA Sinclair, GS Orton, J Fernandes, Y Kasaba, TM Sato, T Fujiyoshi, C Tao, MF Vogt, D Grodent, B Bonfond, JI Moses, TK Greathouse, W Dunn, RS Giles, F Tabataba-Vakili, LN Fletcher, PGJ Irwin
Enhanced mid-infrared emission from CH 4 and other stratospheric hydrocarbons has been observed coincident with Jupiter’s ultraviolet auroral emission 1–3 . This suggests that auroral processes and the neutral stratosphere of Jupiter are coupled; however, the exact nature of this coupling is unknown. Here we present a time series of Subaru-COMICS images of Jupiter measured at a wavelength of 7.80 μm on 11–14 January, 4–5 February and 17–20 May 2017. These data show that both the morphology and magnitude of the auroral CH 4 emission vary on daily timescales in relation to external solar-wind conditions. The southern auroral CH 4 emission increased in brightness temperature by about 3.8 K between 15:50 ut, 11 January and 12:57 ut, 12 January, during a predicted solar-wind compression. During the same compression, the northern auroral emission exhibited a duskside brightening, which mimics the morphology observed in the ultraviolet auroral emission during periods of enhanced solar-wind pressure 4,5 . These results suggest that changes in external solar-wind conditions perturb the Jovian magnetosphere in such a way that energetic particles are accelerated into the planet’s atmosphere, deposit their energy as deep as the neutral stratosphere, and modify the thermal structure, the abundance of CH 4 or the population of energy states of CH 4 . We also find that the northern and southern auroral CH 4 emission evolved independently between the January, February and May images, as has been observed at X-ray wavelengths over shorter timescales 6 and at mid-infrared wavelengths over longer timescales 7 .
All data presented were obtained at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. COMICS observations obtained on 11, 12 January and 19, 20 May were proposed by and awarded to Y.K. using Subaru classical time. COMICS observations on 13, 14 January, 4, 5 February and 17, 18 May were proposed by and awarded to G.S.O. through the Keck-Subaru time exchange programme. We acknowledge the W. M. Keck Observatory, which is operated as a scientific partnership between California Institute of Technology, the University of California and NASA and supported financially by the W. M. Keck Foundation. We recognize and acknowledge the very important cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We thank the NASA Postdoctoral and Caltech programmes for funding and supporting J.A.S. during this research. G.S.O. was supported by grants from NASA to the Jet Propulsion Laboratory/California Institute of Technology.
CitationNature Astronomy, 2019
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
- AM (Accepted Manuscript)