Ghosts of Worlds Passed

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:

Cassini’s Christmas Gift: a Peek at Prometheus

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!

A Shepherd’s Shadow

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

Prometheus Passing

Cassini passes close to Prometheus

Prometheus dips into the F ring

Prometheus, shepherd moon of Saturn’s F ring, is featured in this dramatic raw image from Cassini taken as it passed by at a distance of 23,000 miles on January 27th.

This is the closest yet Cassini has come to Prometheus.

View the official image release on the CICLOPS site here.

Image: NASA/JPL/SSI

ADDED: Here’s another view of Prometheus, this time I tried to clean up the artifacts in the raw file a bit. The full irregular shape of the moon can be seen here.

Another view of Prometheus

Prometheus is about 92 miles long and 42 miles wide.

More great images from the January 27th flyby of Prometheus – including one in color! – and also some of the recently discovered moon Aegaeon can be found on The Planetary Society’s blog here.

Image: NASA/JPL/SSI/J. Major

A Visit to Prometheus

Closeup of Prometheus

This raw image, taken by the Cassini spacecraft on December 26, 2009 (on a certain space blogger’s birthday, by the way) shows an amazing view of Prometheus, one of Saturn’s many shepherd moons.

This is the closest yet that Cassini has come to the 96-mile-long oblong moon. Details of its cratered surface are visible, as is the shadow it casts into the material it pulls from the inner edge of the F ring (part of which can be seen at upper left.) This action is a defining characteristic of the little moon as its tumbling orbit causes it to dip in and out of the bright, icy ring, disturbing the material and pulling out long streamers with its passing.

During the springtime on Saturn, Prometheus’ shadow is often cast directly into the F ring with dramatic effect.

Cassini was approximately 36,000 miles from Prometheus when this image was taken. I rotated the original 90º and adjusted levels slightly to emphasize the moon’s shadow a bit, but otherwise this is the raw image straight from the spacecraft as posted on the CICLOPS site.

Image: NASA/JPL/Space Science Institute