A new series of Hubble Space Telescope images of Saturn has revealed the presence of a series of strange dark spots crisscrossing the planet's rings. Their distribution resembles the spokes of a bicycle wheel, and although the phenomenon usually heralds a change of season, astronomers still cannot explain how and why these "spokes" form, nor the reason for their seasonal variability. The findings have just been published in Geophysical Research Letters. Like Earth, Saturn is tilted on its axis and therefore has four distinct seasons. However, due to the enormous size of its orbit, each of these seasons lasts approximately seven Earth years. Normally, the strange spokes appear only during Saturn’s spring and fall periods, specifically the eight-year period centered on the equinox (when the rings are tilted edge-on to the Sun), and disappear during the summer and winter periods centered on the solstice (when the Sun appears to reach its highest or lowest latitude in the Northern or Southern Hemisphere). Related News standard No. 92-83: Jupiter again leads Saturn in number of moons José Manuel Nieves The International Astronomical Union’s Minor Planet Center officially includes twelve new Jovian satellites discovered in 2021 and 2022 Saturn’s next equinox will occur on May 6, 2025, and as that date approaches, the spokes will become increasingly prominent and observable. In search of the 'culprit' Scientists have long suspected that the variable magnetic field of the ringed giant is to blame for this strange seasonal phenomenon. Here on Earth, the magnetic field interacts with the solar wind and creates an electrically charged environment, so that when these charged particles interact with the atmosphere, they give rise to the fascinating spectacle of the northern lights. In the case of Saturn, scientists suspect that even the smallest of the icy particles that make up the rings can become similarly charged, causing them to temporarily 'levitate' above the rest of the larger ice particles, creating the mysterious spokes. An ingenious explanation, although still unproven. The 'spokes' were first observed by the Voyager mission in the early 1980s, and now, thanks to Hubble's Outer Planet Atmospheres Legacy (OPAL) program, which is building a data archive on the outer planets of our system, it is possible to study the phenomenon over a much longer period, learn about its evolution, and perhaps even determine its origin. Saturn's last equinox occurred in 2009, at the same time that NASA's Cassini spacecraft orbited the giant planet to study it up close. Today, with the Cassini mission ending in 2017 and the Voyager spacecraft millions of miles away, responsibility for the observations falls to Hubble, which continues the long-term work of monitoring changes on Saturn and the other outer planets. Unpredictable Duration “Despite years of excellent observations from the Cassini mission,” says Amy Simon, NASA’s senior planetary scientist, OPAL program manager, and lead author of the paper, “the precise start and duration of the radio season remain unpredictable, just as the first storm during hurricane season is unpredictable.” In short, despite decades of observations, it’s still not entirely clear why these radio spots appear, nor why they are seasonal. Scientists hope that the next few years of Hubble data will help clarify the mystery. MORE INFORMATION news No Five sexual lessons we learned from animals in the last year news No The largest penguin that ever existed: a 'monster bird' as heavy as a gorilla «The Hubble OPAL program - the researchers write in their article - will continue its annual cadence of observing Saturn while the facility is operational, and the radios should soon also be easily visible to ground-based telescopes».
