Hubble Captures Fresh Images Of Saturn's Strange Spokes That Have NASA Mystified

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Enigmatic features across Saturn's rings known as spokes tantalize and baffle NASA scientists. The spokes were first discovered by NASA's Voyager mission in the 1980s, and have been observed in the years preceding and following the planet's equinox. As Saturn's autumnal equinox of the northern hemisphere approaches on May 6, 2025, the mystical spoke season has once again arrived.

In order to study the spoke season in greater detail, NASA's Hubble Space Telescope has time dedicated to Saturn. New images of the ringed planet will be combined with archived data in order to try and answer what causes the "spoke season," as well as their seasonal variability.

"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," explained NASA senior planetary scientist Amy Simon, head of the Hubble Outer Planet Atmospheres Legacy (OPAL) program.

Saturn has four seasons just like Earth, due to axial tilt. However, due to Saturn's larger orbit its seasons each last seven Earth years. The spokes disappear once the planet is close to its summer or winter solstice, but with the autumnal equinox nearing the spokes are expected to be more conspicuous.

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Composite of separate exposures acquired by the Hubble Space Telescope using the WFC3/UVIS instrument.

While scientists are not sure what causes the spokes, they believe it could be due to the planet's variable magnetic field. An example of this is when charged particles hit the atmosphere in the northern hemisphere of Earth, creating the aurora borealis, or northern lights. The thought is 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."

"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," remarked Simon. She added, "It's a fascinating magic trick of nature we only see on Saturn—for now at least."