Hubble Space Telescope Observes Saturn’s “Spoke Season”
Experience the Magnificent Ringworld on a Carousel Ride with Levitated DustGalileo observed Saturn’s peculiar “cup handle” features in 1610, but it would take another 45 years for Christiaan Huygens to characterize them as a disk encircling the planet. Afterwards, only four distinct concentric rings—labeled A, B, C, and D—could be distinguished using ground-based telescopes. NASA’s two Voyager probes did not pass by Saturn until the 1980s, when they took pictures of thousands of concentric rings. Dark, radial spoke-like features on the ring plane that appeared and disappeared as they revolved around Saturn surprised the Voyager scientists even more.
The Hubble Space Telescope has continued where the Voyagers left off throughout the last thirty years. Beside being there, Hubble’s incredibly crisp eyesight is the closest thing. Every year, Hubble rides the “merry-go-round” with ring spokes. The black spokes are thought to represent dust particles that have levitated electrostatically above the ring plane. The seven-year seasons on Saturn appear to cause them to fluctuate greatly. This could also be related to modifications in Saturn’s magnetic field as a result of solar wind turbulence.Hubble Space Telescope Observes Saturn’s “Spoke Season”
On October 22, 2023, the Hubble Space Telescope of NASA captured this image of Saturn from a distance of roughly 850 million miles from Earth. A phenomena known as ring spokes is revealed by Hubble’s incredibly keen vision.
NASA’s Voyager 2 took the first images of the ring spokes in 1981. The spokes were also observed by NASA’s Cassini orbiter during its 13-year mission, which concluded in 2017.
Hubble continues to track Saturn every year, even as its spokes appear and disappear. Hubble’s Outer Planets Atmospheres Legacy (OPAL) program, which started almost ten years ago and tracks yearly weather variations on all four gas-giant outer planets, has recorded this cycle.
The sharp images provided by Hubble demonstrate that spoke apparition frequency is seasonal; spoke apparitions first show up in OPAL data in 2021, but only on the morning (left) side of the rings. The quantity and contrast of the spokes fluctuate with Saturn’s seasons, according to long-term monitoring. Similar to Earth, Saturn has seasons that last roughly seven years due to its tilt on its axis.
“We are heading towards Saturn equinox, when we’d expect maximum spoke activity, with higher frequency and darker spokes appearing over the next few years,” said the OPAL program lead scientist, Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
This year, as they revolve around the enormous globe, these transient structures can be seen simultaneously on both sides of the earth. Despite appearing smaller than Saturn, their length and width exceed the circumference of Earth!
According to Simon, “the predominant theory holds that spokes are derived from some sort of solar interaction with Saturn’s strong magnetic field.” The planet and its rings on Saturn are less inclined away from the Sun when they are close to the equinox. In this arrangement, spoke creation may be enhanced by the solar wind’s increased battering of Saturn’s enormous magnetic field.
Though no hypothesis has been able to explain the spokes precisely for several decades, planetary scientists believe that the electrostatic forces created by this interaction float dust or ice over the ring to form the spokes. A solution to the mystery might someday come from ongoing Hubble observations.
NASA and ESA are working together internationally on the Hubble Space Telescope project. The telescope is operated by NASA’s Goddard Space Flight Center located in Greenbelt, Maryland. The Hubble and Webb science missions are carried out by the Space Telescope Science Institute (STScI) located in Baltimore, Maryland. The Association of Universities for Research in Astronomy in Washington, D.C., manages STScI on behalf of NASA.