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A Visual Demonstration of Gravity, Courtesy of Cassini

Prometheus passes inside Saturn's F ring on Feb. 5 (NASA/JPL-Caltech/SSI. Animation by J. Major)

Prometheus passes inside Saturn’s F ring on Feb. 5 (NASA/JPL-Caltech/SSI. Animation by J. Major)

Prometheus is at it again! On Feb. 5, Cassini acquired a series of images with its narrow-angle camera of Saturn’s reflective and ropy F ring, around the inside of which travels the shepherd moon Prometheus. As it orbits Saturn it regularly arcs outwards toward the inner edge of the F ring and tumbles back inwards again, a scalloping orbit by a potato-shaped moon that yanks at the fine icy particles of the ring with its gravitational tug. However faint they might be, these tidal forces are enough to pull the wispy ring particles into long strands, gaps, and clumps that follow Prometheus’ passage before eventually settling back down again.

The animation above shows a brief segment of this neverending process in play. Click here to read more, and see more images of Prometheus here.

Ghosts of Worlds Passed

Animation of Saturn's F ring and shepherd moons

Animation of Saturn’s F ring and shepherd moons

Saturn’s F ring is a fascinating structure. Made of fine icy particles — most no larger than the particulates found in cigarette smoke — it orbits Saturn just outside the A ring and is easily perturbed by the gravity of nearby moons and embedded moonlets, which create streamers and clumps that rise up in fanciful shapes.

This brief animation, made from 33 raw images captured by Cassini on December 26 (otherwise known locally as my birthday!) shows the F ring in action as it follows shepherd moons Prometheus and smaller Atlas around Saturn. Some motion is due to the orbits of the rings and moons, and some is due to the spacecraft itself.

You can watch a slower version of the animation below:

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Cassini’s Christmas Gift: a Peek at Prometheus

Prometheus on one of its countless trips around Saturn

Potato-shaped Prometheus on one of its countless trips around Saturn

Captured on Christmas Day, this is a raw image from Cassini showing Saturn’s F ring buckling inwards at two places due to the gravitational tug of its inner shepherd moon, Prometheus, seen at center.

As the irregularly-shaped moon approaches the ring material in its looping orbit around Saturn it draws material from the ring in towards itself, warping and stretching the fine icy ring particles into waving streamers that eventually settle back into place. It’s a very visual demonstration of gravity at work!

At its widest Prometheus is about 92 miles (148 km) across but only 42 miles (68 km) in width. It orbits Saturn once every 14.7 hours.

Raw image: NASA/JPL/Space Science Institute

Daphnis Is Back!

Daphnis’ gravity carves waves into the edges of the Keeler gap on Nov. 11, 2012

It’s been a while since I posted an image of my favorite moon of Saturn, but while looking through some recent raw images returned by the Cassini spacecraft I spotted it: Daphnis, the little sculptor shepherd moon!

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A Shepherd’s Shadow

Prometheus casts a shadow through smoky F-ring particles

Inner shepherd of Saturn’s ropy F-ring, Prometheus casts a long shadow through the ring’s icy haze in this beautifully reworked Cassini image by Gordan Ugarkovic.

Discovered by Voyager in 1980 Prometheus completes a tumbling orbit around Saturn every 14.7 hours, regularly dipping into the F-ring in a scalloped path and pulling out streamers of icy particles every time it emerges. At 92 miles long, the potato-shaped moon is only 62 miles across at its widest.

See this image and lots more on Gordan’s Flickr album.

Image: NASA/JPL/SSI/Gordan Ugarkovic.

You say potato, I say Prometheus.


A cratered spud of a moon

Here’s a nicely processed-and-polished photo of Saturn’s moon Prometheus, fresh from the Cassini imaging center at the Space Science Institute in Boulder, CO. Taken during the spacecraft’s flyby of the F-ring’s shepherd moon earlier this year, this image shows Prometheus’ potato-like shape and heavily cratered surface on its trailing side, dimly illuminated by reflected light from Saturn.

See the official image release here.

Image: NASA/JPL/Space Science Institute

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