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Cassini’s Indirect Image of Boulders and Moonlets in Saturn’s Rings

Saturn ring shadows. Credit: NASA/Cassini

Saturn ring shadows. Credit: NASA/Cassini

Take a look at this — it is absolutely stunning. A couple of weeks ago, Anne wrote an article about moon shadows on Saturns rings. Because Saturn is approaching its equinox, in August the rings will “disappear” from our view from Earth, as the rings will be exactly edge-on. But as the rings ease into alignment with the sun, Saturn’s moons cast their shadows across the rings, growing longer as equinox approaches. See in the image above, a shadow is cast on the rings, likely by either the moon Mimas or Tethys. But the eagle-eyed folks over at UnmannedSpaceflight.com also noticed something else in this raw image from the Cassini spacecraft. Notice the area right near the middle of the image where the rings look kind of fuzzy? That’s not just camera blur; those are more shadows, created by thousands of boulders or moonlets in the ring! Amazing! We’ve never actually seen the small objects that make up the rings — and we still haven’t — but we’re seeing the shadows they are creating! Let’s zoom in for a closer look:

Shadows on the rings, closer. Credit: NASA/Cassini/UnmannedSpaceflight.com

Shadows on the rings, closer. Credit: NASA/Cassini/UnmannedSpaceflight.com

Wow! As one of the members of UnmannedSpaceflight said, “Knowledge of the rings’ 3D structure is about to be revolutionized. And let’s not forget that these shadow will get much longer in the coming months.” Let’s zoom in a little more:
Saturn's rings closer yet. Credit: NASA/Cassini

Saturn's rings closer yet. Credit: NASA/Cassini

The UnmannedSpaceflight crew has even created animations from combining several of the raw images sent back by Cassini. In the first movie, it doesn’t look like the moonlet shadows are moving at all, but in a more zoomed in version, it is obvious the shadows are moving as the objects orbit around Saturn. As Stuart Atkinson at Cumbrian Sky said, for a long time we’ve speculated that Saturn’s rings would look a bit like this, close up:
Artist concept of Saturn's rings. Image courtesy NASA/JPL/University of Colorado

Artist concept of Saturn's rings. Image courtesy NASA/JPL/University of Colorado

And now we have the first image of the ring objects, or at least the shadows they create.

Head nod to Stuart Atkinson for the tip, and congrats to the sharp eyes (and image editing prowess) at UnmannedSpaceflight.com for this amazing find! Great work!


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Rafael April 14, 2009, 12:38 PM

    Thanks Stu for that excellent description of a future tour over Saturn’s rings. For some here on earth only the awe brought by extraterrestrial contact, or discovery of an earth-like planet will generate excitement. However, for the rest of us – even the modest indirect detection of boulders tumbling around our beloved ringed giant fires our imagination and gives cause for celebration.

  • IVAN3MAN April 14, 2009, 5:47 PM


    […] Hahaha, you are insane. What the hell are you talking about? Just getting into outer space would be pretty amazing for anybody, but it has nothing to do with shitty shadows on Saturn’s rings. […]

    Obviously, HeadAroundU must have his head where the Sun doesn’t shine!


  • Marco April 14, 2009, 7:58 PM

    Can anyone define the point at which a boulder becomes a moonlet? I have read of some pretty small objects being called moonlets.