Spots the size of Earth have been observed at Jupiter's poles.

The most well-known atmospheric phenomenon of the fifth planet from the Sun — the Great Red Spot — is a persistent high-pressure zone that regularly changes in size. Earlier, Naked Science reported that the shape and size of this atmospheric vortex vary according to a 90-day cycle. However, the reasons behind this phenomenon remain unknown.

Additionally, Jupiter boasts polar auroras: ionized gas (including ionized hydrogen, as well as sulfur and oxygen ions ejected by its moon Io) emits a purple and (less frequently) blue color. These unusually bright phenomena occur in the atmosphere of the gas giant primarily due to the planet's extremely strong magnetic field (10-14 times greater than Earth's magnetic field).

Now, by analyzing data obtained from the Hubble Space Telescope between 1994 and 2022, a research team from the University of California (USA) has discovered unusual oval structures at Jupiter's northern and southern poles. The spots, which are only visible in the ultraviolet range, were found to appear 75 percent of the time at the southern pole, but they are extremely rare at the northern pole — they were recorded only once in eight observations.

The discovery, according to the authors of the scientific paper published in the journal Nature Astronomy, indicates that the southern pole of the gas giant is more susceptible to processes that lead to the formation of spots. These spots, as noted by lead author Troy Tsubota, almost always appear beneath the bright zones of Jupiter's auroras and absorb more ultraviolet radiation than the surrounding atmosphere. That is why they appear darker in images.

The research team hypothesized that these mysterious structures arise from the interaction between the planet's magnetic field and its atmosphere — at the core of the phenomenon is likely a powerful anticyclonic vortex formed by the interaction of Jupiter's ionosphere and the plasma torus created by Io. It is worth noting that this volcanically active moon ejects 1,000 kilograms of ionized gas into space every second, which subsequently forms a torus surrounding the gas giant along the moon's orbit.

“This vortex resembles a tornado that reaches the lower layers of the atmosphere and mixes stratospheric gases. As a result of these processes, dense areas of haze are formed, which can lead to an increase in aerosol concentration by 50 times compared to normal levels,” explained co-author of the study, astronomer Michael Wong.

The results indicated that processes within Jupiter's magnetosphere affect its atmosphere more significantly than previously thought: the interaction of magnetic fields and plasma flows leads to dynamic processes that form vortices. The phenomena observed by astronomers appear particularly contrasting when compared to conditions on Earth — on our planet, such magnetic processes predominantly affect the upper layers of the atmosphere, causing auroras.

Astronomers noted that studying the connections between different layers of the atmosphere is crucial for understanding the dynamics of the atmospheres of any planets, whether it be Jupiter, Earth, or worlds beyond our Solar System (exoplanets). Further observations of the polar regions of the gas giant will help scientists learn more about the mechanisms behind the formation of dark spots and their impact on the planet's atmosphere. 

The discovery was part of the OPAL (Outer Planet Atmospheres Legacy) program and may lead to the development of more accurate models of planetary atmospheres in the future, allowing for a better understanding of their dynamics and evolution over time.