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- Title
Hubble Detects the Start of a New Saturn Ring Spoke Season.
- Authors
Simon, Amy A.; Hedman, Matthew M.; Nicholson, Philip D.; Tiscareno, Matthew S.; Showalter, Mark R.; McDonald, Troy; Callos, Samantha
- Abstract
Saturn's ring spokes typically appear over an 8‐year duration centered on equinox. Hubble Space Telescope observations in 2021 indicate the beginning of a new spoke season as Saturn approaches equinox in 2025. The spokes show increased contrast and longevity in 2022, persisting for up to 11 hours. The spokes are visible from UV to near‐IR and are slightly bluer (i.e., less red) than the rings, but we find no significant wavelength dependence in the spectral contrast, which approximates their optical depth). Spoke rotation rates are between 606 and 626 min, consistent with either Keplerian rotation or possibly the variable rotation rate of Saturn's kilometric radiation. Spoke activity is expected to increase over the next several years. Plain Language Summary: 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. Hubble Space Telescope observations in 2021 and 2022 revealed the start of a new ring spoke season in advance of the next equinox in 2025. Multi‐color observations reveal 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. Spoke activity should continue to increase for the next several years, becoming more visible to ground‐based telescopes over time. Key Points: The start of a new Saturn spoke season was confirmed by Hubble observations in 2021 and 2022, with spokes tracked over an 11‐hr periodThe spokes occurred near 1.8 Saturn radii and are spectrally red, but slightly bluer than the ringsSpoke activity and contrast is expected to increase as ring opening angle decreases in advance of Saturn's next equinox in May 2025
- Subjects
SATURN (Planet); AUTUMNAL equinox; SPACE telescopes; VERNAL equinox; SEASONS
- Publication
Geophysical Research Letters, 2023, Vol 50, Issue 3, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2022GL101904