A brightening of Jupiter’s auroral 7.8-μm CH4 emission during a solar-wind compression

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 .