Mysterious "spoke season" captured on Saturn

Today’s Video of the Day from NASA Goddard Space Flight Center features images of Saturn from NASA’s Hubble Space Telescope. The photographs capture the start of the mysterious “spoke season” on Saturn – when unexplained features appear on its rings. 

According to NASA, both the cause of the spokes and their seasonal variability have yet to be fully explained by planetary scientists.

“Like Earth, Saturn is tilted on its axis and therefore has four seasons, though because of Saturn’s much larger orbit, each season lasts approximately seven Earth years. Equinox occurs when the rings are tilted edge-on to the Sun,” explains NASA.

“The spokes disappear when it is near summer or winter solstice on Saturn. (When the Sun appears to reach either its highest or lowest latitude in the northern or southern hemisphere of a planet.) As the autumnal equinox of Saturn’s northern hemisphere on May 6, 2025, draws near, the spokes are expected to become increasingly prominent and observable.”

Experts believe that the spokes may be a product of the planet’s variable magnetic field. When magnetic fields interact with solar wind, an electrically charged environment is created. This phenomenon is visible on Earth as the northern lights. 

“Scientists think that the smallest, dust-sized icy ring particles can become charged as well, which temporarily levitates those particles above the rest of the larger icy particles and boulders in the rings,” says NASA.

The spokes were first observed in the early 1980s by NASA’s Voyager mission. Depending on the angle of the rings, the spokes can appear dark or light.

“Thanks to Hubble’s OPAL program, which is building an archive of data on the outer solar system planets, we will have longer dedicated time to study Saturn’s spokes this season than ever before,” said NASA senior planetary scientist Amy Simon, head of the Hubble Outer Planet Atmospheres Legacy (OPAL) program.

“Despite years of excellent observations by the Cassini mission, the precise beginning and duration of the spoke season is still unpredictable, rather like predicting the first storm during hurricane season.”

Video Credit: NASA Goddard 

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By Chrissy Sexton, Earth.com Editor

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