Saturn, like Earth, has four seasons because of its tilted axis. However, due to Saturn’s far bigger orbit, each season lasts roughly seven Earth years.
The “spoke season” surrounding Saturn’s equinox, when enigmatic markings start to form across its rings, has begun, according to new photographs of the planet from NASA’s Hubble Space Telescope. Planetary scientists still do not fully understand the spokes’ origin and seasonal variability.
An equinox occurs when the rings are tilted edge-on to the Sun. The spokes disappear when it is near the summer or winter solstice on Saturn.
The most recent equinox on Saturn happened in 2009 when NASA’s Cassini mission was orbiting the gas giant planet for up-close observation.
The spokes are projected to become more prominent and detectable as the autumnal equinox of Saturn’s northern hemisphere on May 6, 2025, draws near.
NASA’s Voyager mission first observed the ring spokes in the early 1980s. They appear dark or light depending on the illumination and viewing angles.
The planet’s fluctuating magnetic field is thought to be the cause of the spokes. Solar wind and planetary magnetic fields combine to produce an electrically charged atmosphere. According to scientists, even the tiniest dust-sized icy ring particles have the potential to charge up and rise momentarily above the 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, rather like predicting the first storm during hurricane season.”
“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.”
“While our solar system’s other three gas giant planets also have ring systems, nothing compares to Saturn’s prominent rings, making them a laboratory for studying spoke phenomena. Whether spokes could or do occur at other ringed planets is currently unknown. It’s a fascinating magic trick of nature we only see on Saturn—for now, at least.”
- Amy A. Simon, et al. Hubble Detects the Start of a New Saturn Ring Spoke Season. Geophysical Research Letters (2023). DOI: 10.1029/2022GL101904