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Aerosols in Jupiter’s stratosphere form intriguing polar hoods, which have been investigated by ultraviolet cameras on Cassini and the Hubble Space Telescope. Transient, concentrated dark ovals of unknown origin have been noted within both the northern and southern polar hoods. However, a systematic comparative study of their properties, which could elucidate the physical processes active at the poles, has not yet been performed due to infrequent observations. Using 26 global maps of Jupiter taken by Hubble between 1994 and 2022, we detected transient ultraviolet-dark ovals with a 48% to 53% frequency of occurrence in the south. We found the southern dark oval to be 4 to 6 times more common than its northern counterpart. The southern feature is an anticyclonic vortex and remains within the auroral oval during most of its lifetime. The oval’s darkness is consistent with a 20 to 50 times increase in haze abundance or an overall upward shift in the stratospheric haze distribution. The anticyclonic vorticity of the dark oval is enhanced relative to its surroundings, which represents a deep extension of the higher-altitude vortices previously reported in the thermosphere and upper stratosphere. The haze enhancement is probably driven by magnetospheric momentum exchange, with enhanced aerosols producing the localized heating detected in previous infrared retrievals. 

Abstract The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune–Triton system. This bold mission of exploration would orbit an ice-giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon Triton. Triton is a captured dwarf planet from the Kuiper Belt, twin of Pluto, and likely ocean world. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Between Uranus and Neptune, the latter is unique in providing simultaneous access to both an ice giant and a Kuiper Belt dwarf planet. The spacecraft—in a class equivalent to the NASA/ESA/ASI Cassini spacecraft—would launch by 2031 on a Space Launch System or equivalent launch vehicle and utilize a Jupiter gravity assist for a 12 yr cruise to Neptune and a 4 yr prime orbital mission; alternatively a launch after 2031 would have a 16 yr direct-to-Neptune cruise phase. Our solution provides annual launch opportunities and allows for an easy upgrade to the shorter (12 yr) cruise. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), using the moon's gravity to shape the orbital tour and allow coverage of Triton, Neptune, and the space environment. The atmospheric entry probe would descend in ∼37 minutes to the 10 bar pressure level in Neptune's atmosphere just before Odyssey's orbit-insertion engine burn. Odyssey's mission would end by conducting a Cassini-like “Grand Finale,” passing inside the rings and ultimately taking a final great plunge into Neptune's atmosphere.