Recent observations by the Hubble Space Telescope have revealed dark spots the size of Earth at Jupiter's poles, likely caused by magnetic vortices concentrated in hydrocarbon haze.
These transient phenomena, visible in ultraviolet light, occur more frequently at the southern pole, indicating a profound connection between Jupiter's magnetic field and its atmospheric dynamics.
While Jupiter's Great Red Spot has captivated astronomers for centuries, researchers from the University of California, Berkeley, have uncovered a new mystery: massive polar spots that appear and disappear unpredictably, unlike the persistent Great Red Spot.
These dark spots, visible only in ultraviolet light, are hidden within dense layers of stratospheric haze covering Jupiter's poles. They typically appear beneath the brighter areas of the polar auroras, resembling Earth's northern and southern lights. In ultraviolet images from Hubble, these spots stand out due to their higher absorption of ultraviolet light compared to their surroundings, giving them a darker appearance.
Between 2015 and 2022, annual observations from Hubble showed that a dark ultraviolet spot appeared at Jupiter's southern pole in 75% of cases, while similar spots at the northern pole were observed in only one out of eight images.
The dark ultraviolet spots suggest extraordinary processes occurring within Jupiter's strong magnetic field, advancing towards the poles and penetrating deep into the atmosphere, significantly more powerful than the magnetic processes creating auroras on Earth.
The phenomenon was reported by researchers from the University of California and their colleagues on November 26 in the journal Nature Astronomy.
Dark ultraviolet spots were first identified by Hubble in the late 1990s at both poles and later at the northern pole by the Cassini spacecraft during its flyby of Jupiter in 2000, but they received little attention. Undergraduate student Troy Tsoubotas conducted a systematic study of recent images captured by Hubble, discovering that this phenomenon is common at the southern pole—identifying eight southern dark structures (SUDOs) between 1994 and 2022. In contrast, only two northern dark structures (NUDOs) were found among 25 global maps captured by Hubble showing the northern pole.
Most images were collected as part of the Outer Planet Atmospheres Legacy (OPAL) project, led by planetary scientist Amy Simon at NASA's Goddard Space Flight Center and one of the paper's co-authors. Through OPAL, astronomers conduct annual observations of Jupiter, Saturn, Uranus, and Neptune to understand their atmospheric dynamics and evolution over time.
“Within two months, we realized that the OPAL images were like a goldmine, and I quickly developed a way to analyze and submit all the images for review,” said Tsoubotas, a fourth-year student at Berkeley majoring in physics, mathematics, and computer science. “Then we understood we could conduct significant science and analyze real data.”
Wong and Tsoubotas consulted with planetary atmospheric experts—Tom Stallard from Northumbria University and Zhi Zhang from the University of Santa Cruz—to understand what might be causing these regions of dense haze. Stallard hypothesized that the dark spot is likely formed by a vortex caused by friction between magnetic field lines in the ionosphere and plasma ejected from Jupiter's volcanic moon, Io.
“The haze in the dark structures is 50 times denser than typical concentrations,” Zhang noted, “indicating that it is likely formed through vortex dynamics rather than chemical reactions caused by energetic particles from the upper atmosphere.”