Researchers from UC Berkeley have identified large, transient dark ovals at Jupiter's north and south poles, similar in size to the Great Red Spot. These features, visible only in ultraviolet wavelengths, are embedded within the planet's stratospheric haze.
These dark ovals frequently appear just beneath the bright auroral regions at each pole, resembling Earth's northern and southern lights. They absorb more ultraviolet light than their surroundings, making them visible in images captured by NASA's Hubble Space Telescope. Observations from Hubble between 2015 and 2022 show that a dark UV oval appears at the south pole 75% of the time, while similar features at the north pole are present in only one out of eight images.
These dark UV ovals suggest unusual processes occurring within Jupiter's strong magnetic field, extending deep into the atmosphere, unlike the magnetic processes that create auroras on Earth. The phenomenon was reported in the journal Nature Astronomy.
Initially detected in the late 1990s by Hubble and later by the Cassini spacecraft in 2000, these ovals received little attention until a systematic study by UC Berkeley student Troy Tsubota revealed them as a common feature at the south pole. Between 1994 and 2022, Tsubota identified eight dark UV ovals (SUDOs) in the south, while only two dark UV ovals (NUDOs) were found in 25 global maps of the north pole.
The majority of Hubble images were part of the Outer Planet Atmospheres Legacy (OPAL) project, which conducts annual observations of the outer planets to understand their atmospheric dynamics. Tsubota and lead author Michael Wong consulted experts Tom Stallard and Xi Zhang to explore potential causes for these dense haze regions.
Stallard theorized that the dark ovals might be influenced by a vortex created when the planet's magnetic field lines encounter friction at distant locations, stirring the atmosphere. This vortex spins rapidly in the ionosphere, gradually weakening as it descends. The dynamics resemble a tornado interacting with the atmosphere, creating the observed dark patches.
The team suspects these phenomena form over approximately a month and dissipate within weeks.