The Sciences

More Saturn ring awesomeness

Bad AstronomyBy Phil PlaitAug 10, 2009 11:00 AM


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Yesterday, I wrote about a weird event at Saturn, where some object apparently blasted through Saturn's rings. But that's not the only cool thing that's happened out there. As I mentioned in that post, Saturn's rings are almost exactly edge-on to the Sun, meaning that anything that sticks out above the phenomenally flat rings will cast a long, long shadow. We're seeing more and more of that as the rings aim themselves at the Sun -- with them being exactly aligned with the Sun -- the Saturnian equinox, as it were -- on August 11, tomorrow! Even now there are wonders to behold. Saturn's narrow F ring, outside the main A ring, has been getting tortured, twisted, manipulated by the gravity of nearby moons. Whenever some event or another moves particles in the rings above or below the ring plane, they cast one of these reaching shadows. We're so close to the equinox now that shadows fall a long way indeed:

Check that out! Whatever that lump is that you can barely see in the F ring (I marked it with an arrow to help you see it), it's casting a shadow over 5000 kilometers long -- the width of the entire United States. The shadow is a little faint, but that's because Cassini was looking at the unlit side of the rings, so we're in essence seeing this shadow literally through the rings themselves. Had the spacecraft been on the other side, the shadow would have been a lot more obvious. Incidentally, Cassini was almost 1.8 million kilometers (1.1 million miles) from the shadow when it took this image; that's four and a half times the distance of the Moon from the Earth. This image was taken on July 30, still two weeks before the equinox. What will we see on that exact moment, when the Sun shines straight down the knife-edge of the rings? A dozen shadows of moons as they circle hundreds of thousands of kilometers outside the rings? A vast array of parallel linear features caused by countless irregularities in the rings' otherwise planar structure? I can't wait to find out! But one thing I already know: Saturn will surprise us. It has an infinite capacity for that.

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