While Jupiter’s Great Red Spot has been a constant feature of the planet for centuries, University of California, Berkeley, astronomers have discovered equally large spots at the planet’s north and south poles that appear and disappear seemingly at random.
The Earth-size ovals, which are visible only at ultraviolet wavelengths, are embedded in layers of stratospheric haze that cap the planet’s poles. The dark ovals, when seen, are almost always located just below the bright auroral zones at each pole, which are akin to Earth’s northern and southern lights. The spots absorb more UV than the surrounding area, making them appear dark on images from NASA’s Hubble Space Telescope. In yearly images of the planet taken by Hubble between 2015 and 2022, a dark UV oval appears 75% of the time at the south pole, while dark ovals appear in only one of eight images taken of the north pole.
The dark UV ovals hint at unusual processes taking place in Jupiter’s strong magnetic field that propagate down to the poles and deep into the atmosphere, far deeper than the magnetic processes that produce the auroras on Earth.
The UC Berkeley researchers and their colleagues reported the phenomena today (Nov. 26) in the journal Nature Astronomy.
Dark UV ovals were first detected by Hubble in the late 1990s at the north and south poles and subsequently at the north pole by the Cassini spacecraft that flew by Jupiter in 2000, but they drew little attention. When UC Berkeley undergraduate Troy Tsubota conducted a systematic study of recent images obtained by Hubble, however, he found they were a common feature at the south pole — he counted eight southern UV-dark ovals (SUDO) between 1994 and 2022. In all 25 of Hubble’s global maps that show Jupiter’s north pole, Tsubota and senior author Michael Wong, an associate research astronomer based at UC Berkeley’s Space Sciences Laboratory, found only two northern UV-dark ovals (NUDO).