Hubble's ultra-clear view reveals the ring spoke phenomenon

The rising dust takes a circular tour around the giant ring world

althoug SaturnThe unusual “cup-handle” features were first observed by Galileo in 1610, and it was another 45 years before Christian Huygens described it as a disk surrounding Saturn. Later, ground-based telescopes could only distinguish four unique concentric rings, designated A, B, C, and D. This was not done until the 1980s. NASAThe Voyager probes fly by Saturn to photograph thousands of concentric rings. The biggest surprise to Voyager scientists was the dark, radial, ring-like patterns that come and go as it orbits Saturn.

Over the past three decades, Hubble Space Telescope He picked up where the travelers left off. Hubble's ultra-clear view is the next best thing to being there. Hubble tracks the “merry vortex” every year. The dark spokes are thought to be dust particles raised electrostatically above the annular plane. They seem to change frequently with Saturn's seven-year seasons. This may be related to changes in Saturn's magnetic field, as it is exposed to the solar wind.

This is an annotated version of the image above. Image credit: NASA, ESA, STScI, Amy Simon (NASA-GSFC)

The Hubble Space Telescope observes the “speaking season” on Saturn

This image of Saturn was taken by NASA's Hubble Space Telescope on October 22, 2023, when the ringed planet was about 850 million miles from Earth. Hubble's ultra-clear view reveals a phenomenon called ring spokes.

Saturn's spokes are fleeting features that rotate with the rings. Its ghostly appearance only lasts for two or three orbits around Saturn. During periods of activity, newly formed wires continually add to the pattern.

In 1981, NASA's Voyager 2 spacecraft photographed the ring spoke for the first time. NASA Cassini The orbiter also saw the speaker during its 13-year mission that ended in 2017.

Hubble continues to monitor Saturn annually as the spokes come and go. This cycle was captured by Hubble's Outer Planets Atmospheres Legacy (OPAL) program, which began nearly a decade ago to monitor weather changes annually on all four gas giant exoplanets.

Clear Hubble images show that the frequency of spoked apparitions is seasonally driven, as they first appeared in the OPAL data in 2021 but only on the morning (left) side of the rings. Long-term observations show that both the number and variance of spokes vary with Saturn's seasons. Saturn is tilted on its axis like Earth and has seasons that last about seven years.

“We are heading toward the Saturnian equinox, when we expect maximum speaker activity, with higher frequencies and darker plumes emerging over the next few years,” said Opal program principal scientist Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland. .

This year, these ephemeral structures appear on both sides of the planet simultaneously as they orbit the giant globe. Although it looks small compared to Saturn, its length and width can extend longer than the Earth's diameter!

“The leading theory is that the wires are connected to Saturn's strong magnetic field, with some sort of solar interaction with the magnetic field giving you the speaker,” Simon said. When it approaches the equinox on Saturn, the planet and its rings are tilted less away from the sun. In this configuration, the solar wind may hit Saturn's massive magnetic field with greater force, promoting the formation of the lines.

Planetary scientists believe that electrostatic forces generated by this interaction lift dust or ice above the ring to form the spokes, although after several decades there is no theory that perfectly predicts the beam. Continued Hubble observations may finally help solve the mystery.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts science operations on Hubble and Webb. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, DC