Saturn, like Earth, has four seasons because of its tilted axis. However, due to Saturn’s much larger orbit, each season lasts about seven Earth years.

The “spoke season” around Saturn’s equinox, when puzzling markings begin to form over the rings, has begun, according to new images of the planet from NASA’s Hubble Space Telescope. Planetary scientists still don’t fully understand the origin and seasonal variability of the spokes.

An equinox occurs when the rings are tilted edge-to-edge toward the sun. The spokes disappear when it is near the summer or winter solstice on Saturn.

The most recent equinox on Saturn occurred in 2009 when NASA’s Cassini mission orbited the gas giant planet for close-up observation.

The spokes are expected to become more prominent and more noticeable as the autumnal equinox of Saturn’s northern hemisphere on May 6, 2025 approaches.

NASA’s Voyager mission first observed the ring spokes in the early 1980s. They appear dark or light depending on the lighting and viewing angles.

The fluctuating magnetic field of the planet is believed to be the cause of the spokes. Solar wind and planetary magnetic fields combine to create an electrically charged atmosphere. According to scientists, even the tiniest dust-sized icy ring particles have the potential to charge up and momentarily rise above surrounding larger frozen particles and boulders.

NASA senior planetary scientist Amy Simon, head of the Hubble Outer Planet Atmospheres Legacy (OPAL) program, said: “Despite years of excellent observations by the Cassini mission, the precise beginning and duration of the spoke season is still unpredictable, similar to predicting the first storm during hurricane season.”

“Thanks to Hubble’s OPAL program, which is building an archive of data on the outer planets of the solar system, we will have more time this season to study Saturn’s spokes than ever before.”

“While the other three gas giant planets in our solar system also have ring systems, nothing compares to Saturn’s prominent rings, making them a laboratory for studying spoke phenomena. Whether spokes can or will occur on other ringed planets is currently unknown. It’s a fascinating magic trick of nature that we only see on Saturn – at least for now.”

Magazine reference:

  1. Amy A. Simon, et al. Hubble Detects the Beginning of a New Saturn Ring Spoke Season. Geophysical Survey Letters (2023). DOI: 10.1029/2022GL101904