Evrim Yazgin
Cosmos science journalist
Earth-sized magnetic tornadoes at Jupiter’s poles have astronomers scratching their heads.
The dark ovals were first seen by the Hubble Space Telescope in the 1990s. Images of Jupiter taken in 2015 and 2022 also show the storms. The Cassini spacecraft also spotted the dark objects during its flyby in 2000. But they drew little attention.
Researchers have now published a paper in Nature Astronomy which hints that the storms are linked to unusual processes in Jupiter’s magnetic field.
The dark ovals are almost as large as Jupiter’s famous Great Red Spot which has been a constant feature visible on the planet for centuries.
The storms are only visible at ultraviolet wavelengths. Because they absorb more UV light than the surrounding areas, they appear as dark spots. They sit in the haze that caps Jupiter’s poles, just below the bright zones which are akin to the aurora on Earth.
The new study reveals the spots are common on Jupiter’s south pole, but rare in the north.
Between 1994 and 2022, Hubble images show 8 southern UV-dark ovals (SUDO). In 25 Hubble images showing the north pole, however, only 2 northern UV-dark ovals (NUDO) are visible.
Dark ovals are likely generated from above by vortices created when the planet’s magnetic field lines experience friction in Jupiter’s ionosphere – a part of the upper atmosphere where solar radiation has ionised atoms and molecules to create a layer of electrons.
The researchers suggest that the vortex weakens as it gets into deeper layers. Like a tornado touching down on dusty ground on Earth, the vortex on Jupiter stirs up the haze near the poles to create the dense spots observed in the images.
Observations show the ovals form over the course of a month and dissipate in a couple of weeks.
“The haze in the dark ovals is 50 times thicker than the typical concentration, which suggests it likely forms due to swirling vortex dynamics rather than chemical reactions triggered by high-energy particles from the upper atmosphere,” says co-author Xi Zhang from the University of California, Santa Cruz.
“Our observations showed that the timing and location of these energetic particles do not correlate with the appearance of the dark ovals.”
“Studying connections between different atmospheric layers is very important for all planets, whether it’s an exoplanet, Jupiter or Earth,” says senior author Michael Wong from the University of California, Berkeley.
