Saturn is known for its iconic, pristine rings. However, the main B ring can have splotches and streaks of darker or lighter material, known as spokes, that may be tied to dust interactions with the planet’s magnetic field. These spokes appear periodically, lasting around 8 years, centered around Saturn spring or fall equinox. In 2021 and 2022, observations using the NASA/ESA Hubble Space Telescope revealed the start of a new ring spoke season in advance of the next equinox in 2025. Multi-color observations revealed a reddish color, and that the spokes circle the planet at about the same rate as the ring particles, though perhaps influenced by the variable rotation rate of Saturn’s magnetosphere.
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.
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.
The suspected culprit for the spokes is the planet’s variable magnetic field.
Planetary magnetic fields interact with the solar wind, creating an electrically charged environment. On Earth, when those charged particles hit the atmosphere this is visible in the northern hemisphere as the aurora borealis.
Astronomers 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.
The ring spokes were first observed by NASA’s Voyager mission in the early 1980s.
The transient, mysterious features can appear dark or light depending on the illumination and…
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