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astronomy, cassini mission

Messing With the F Ring

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What Two Moons Can Do

The shredded F ring of Saturn, as seen by the Cassini-Huygens mission narrow-angle camera on January 11, 2009. (Click to embiggen.)
The shredded F ring of Saturn, as seen by the Cassini-Huygens mission narrow-angle camera on January 11, 2009. (Click to embiggen.)

Earlier this year the Cassini-Huygens mission studied the delicate F ring that winds a delicate strand of debris around Saturn. The F ring is the outermost of the rings and is only a few hundred kilometers wide.

It turns out that the F-ring is disrupted by the action of the two moons that also work to keep it on the clumpy and narrow. Prometheus and Pandora both interact with the ring, and occasionally they work to disrupt the material in the ring — giving it a somewhat jagged, clumpy, and very ethereal appearance. Prometheus’s orbit encounters the ring and when it does, this tiny moon’s gravitational pull tugs at the ring material, causing the disrupted appearance. It’s almost as if the moonlet is slicing material out of the ring as they move along together around Saturn.

Animation showing how two moons sculpt and disrupt the F ring at Saturn. (Click to embiggen.)
Animation showing how two moons sculpt and disrupt the F ring at Saturn. (Click to embiggen.)

The F ring is made of particles of ice and dust that swarm in orbit around the planet, and was first seen in images from the Pioneer spacecraft. Subsequent Voyager images showed more detail in the ring — and at that time, I remember scientists referring to the “kinky” F ring because of the mysterious knotted structure they were seeing in the Voyager images.

If you could be in a spacecraft hovering above the F ring and watch it for a few hours, you’d see the view changing continually, as it appears to do in this animation (below).  Amazing what we can learn by watching for just a few hours, eh?

cassini mission, enceladus, planetary science, planets

Going South for the Summer

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Cassini at Enceladus: More!  More!

These are the infamous tiger stripes in the region on Enceladus where Cassini scientists spotted material coming out of vents.  It’s a false-color mosaic–meaning that several sets of images from the Imaging Subsystem were pieced together and colored to highlight specific units of the surface that scientists want to study. Here’s what the Cassini mission press release has to say about this image:

Areas that are greenish in appearance are believed to represent deposits of coarser grained ice and solid boulders that are too small to be seen at this scale, but which are visible in the higher resolution views, while whitish deposits represent finer grained ice. The mosaic shows that coarse-grained and solid ice are concentrated along valley floors and walls, as well as along the upraised flanks of the “tiger stripe” fractures, which may be covered with plume fallout that landed not far from the sources. Elsewhere on Enceladus, this coarse water ice is concentrated within outcrops along cliff faces and at the top of ridges. The sinuous boundary of scarps and ridges that encircles the south polar terrain at about 55 degrees south latitude is conspicuous. Much of the coarse-grained or solid ice along this boundary may be blocky rubble that has crumbled off of cliff faces as a result of ongoing seismic activity.

Wouldn’t it be fun to hike this area? Perhaps in the future, planetary geologists will bring their equipment here to sample the surface, measure its properties, and give all of us here on Earth the ultimate close-up pictures of this fascinating moon.

Just to give you an idea what Voyager 2 saw, here’s the image we all marvelled over 27 years ago this month. Even then, we were all fascinated with the juxtaposed terrains and mysterious cracks on this icy surface.  What a difference nearly three decades makes!

I’ve written before about the scene at Jet Propulsion Laboratory in Pasadena that night, when Enceladus showed us her stuff. It was a noisy, wonderful experience, made even  more exciting by the fact that when this picture came down from the Deep Space Network and scanned across the screen, it was during a live broadcast of Nightline. A lot of science writers and planetary scientists were standing around watching, and thus we were all together in one big happy family jabbering to each other about what we were seeing on the screens. We made so much noise when we saw the pics that the floor directors for Nightline had to shush us several times, pretty much to no avail!  Hey… we were watching planetary science history unfold before our eyes.  With all due respect to Ted Koppel, Enceladus was far more fetching and mysterious, and we weren’t going to let the chance go by to do instant science interpretation on that amazing image!