Bright spokes in Saturn’s rings
Click for original image.
Cool image time! The picture to the right, cropped slightly to post here, was taken on December 26, 2008 from a distance of 350,000 miles by the Cassini spacecraft as it orbited Saturn. The resolution is about 37 miles per pixel.
I think sunlight is coming from the upper left, its light bouncing off the rings and thus making the those spokes bright and visible.
In the viewing geometry in which Cassini is looking approximately in the direction of the sun (called high phase), the spokes appear white against the rings because the very small particles comprising the spokes preferentially scatter light forward (in this case, toward Cassini).
At least that’s one theory for explaining the spokes that appear randomly and for only short periods within Saturn’s rings, sometimes bright, sometimes dark, depending on the angle of the Sun. According to a Hubble press release from 2023, the spokes are formed due to an interaction between Saturn’s magnetic field, the solar wind, and the tiny particles in the rings.
“The leading theory is that spokes are tied to Saturn’s powerful magnetic field, with some sort of solar interaction with the magnetic field that gives you the spokes,” said Simon. When it’s near the equinox on Saturn, the planet and its rings are less tilted away from the Sun. In this configuration, the solar wind may more strongly batter Saturn’s immense magnetic field, enhancing spoke formation.
Planetary scientists think that electrostatic forces generated from this interaction levitate dust or ice above the ring to form the spokes, though after several decades no theory perfectly predicts the spokes. [emphasis mine]
Just another strange alien phenomenon in space that remains unsolved. All we really know is that the spokes appear, remain visible for at most a rotation or two of the rings, and then disappear.
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I remember when both Pioneer 11 and Voyagers 1 and 2 made their flybys of Saturn.
Pioneer 11 took a few pictures and, even then, there were indications that much of what was known about the rings would soon change. For example, the gaps between the rings appeared to be filled with material.
Voyager 1 confirmed that and then went on to find that observation was correct. One of the interesting things found in the pictures it sent back were the braided rings. (Those were believed to be caused by interactions with moons inside the ring structure.) Then there were the spokes, which, as noted, still baffle scientists.
Back then, it was front-page news for several days.