The Great Cold Spot in Jupiter's upper atmosphere

Past observations and modeling of Jupiter's thermosphere have, due to their limited resolution, suggested that heat generated by the aurora near the poles results in a smooth thermal gradient away from these aurorae, indicating a quiescent and diffuse flow of energy within the subauroral thermosphere. Here we discuss Very Large Telescope-Cryogenic High-Resolution IR Echelle Spectrometer observations that reveal a small-scale localized cooling of similar to 200K within the nonauroral thermosphere. Using Infrared Telescope Facility NSFCam images, this feature is revealed to be quasi-stable over at least a 15year period, fixed in magnetic latitude and longitude. The size and shape of this Great Cold Spot vary significantly with time, strongly suggesting that it is produced by an aurorally generated weather system: the first direct evidence of a long-term thermospheric vortex in the solar system. We discuss the implications of this spot, comparing it with short-term temperature and density variations at Earth. Plain Language Summary In this paper, we reveal the detection of a region of cooling in Jupiter's upper atmosphere that we describe as Jupiter's Great Cold Spot. In the past, Jupiter's upper atmosphere was observed to have a gentle gradient of heat flowing away from the auroral region, and so the detection of such a localized cooling suggests that Jupiter's upper atmosphere is far more complex than previously thought. This region, similar in size to the Great Red Spot, appears to be a large vortex located at very high altitudes, but unlike weather systems lower in the atmosphere, it appears to be directly related to the planet's aurora. This vortex has been observed over 15 years and so appears to be somewhat stable, though it changes in shape and size over shorter timescales. Although never considered for Jupiter, this vortex might be related to similar structures observed and modeled at Earth.