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Emily LakdawallaSeptember 1, 2009

Cassini goodies: Telesto, Janus, Prometheus, Pandora, F ring

As I mentioned yesterday, the Cassini raw images website has been full of goodies lately. Here's a sample.

(First, a quick update on the Station fire: Mount Wilson is still unscathed, and firefighters predict today will be a better day. Concern is abating.)

My favorite recent set of images was targeted at Janus. Take a look at this animation and see if you can figure out what's going on before you read any further:


Janus is the 10th largest moon of Saturn, 196 x 192 x 150 kilometers in diameter and orbits along with Epimetheus between the F and G rings.
Did you figure it out? As the sequence starts, Janus is in eclipse -- it's in the shadow of Saturn's rings. But as Cassini watched, a gap in Saturn's rings crossed the moon, making a broad stripe of sunlight that moved from pole to pole. The gap appeared to have one sharp edge and one more transparent edge. I don't know which gap in the rings that was -- could have been the Keeler gap, maybe. I think I enjoy this animation especially because it's sort of like the evil alternate universe version of one of my favorite image series from the Voyager Saturn encounter:
Epimetheus from Voyager 1

NASA / JPL / animation by Emily Lakdawalla

Epimetheus from Voyager 1
On November 12, 1980, Voyager 1 captured a series of images of Epimetheus through different color filters. During the sequence, the shadow of the F ring crossed the moon.
Recently Cassini also had a nice close look at Telesto, the trailing companion to Tethys. These Lagrangian moons look very very dusty; the Lagrange points of orbits must be a spot that collects Saturn's versions of dust bunnies.

NASA / JPL / SSI / color composite by Gordan Ugarkovic

Cassini captured this view of the leading hemisphere of Telesto on August 27, 2009. Telesto is a small moon, 34 x 28 x 36 kilometers in diameter, that occupies a Lagrange point behind Tethys in its orbit around Saturn. This is an approximately natural color view composed of raw images.
The image compliments nicely an earlier one of Telesto, which shows primarily the trailing hemisphere.
Saturn's moon Telesto

NASA / JPL / Space Science Institute

Saturn's moon Telesto
This raw image was captured by Cassini during its closest planned encounter with Telesto, on October 11, 2005.
Here's one more nice recent animation, showing the gores in the F ring created by Prometheus traveling around the ring ansa. Saturn is such a pretty place!
Prometheus, Pandora, and the F ring

NASA / JPL / SSI / animation by Mike Malaska

Prometheus, Pandora, and the F ring
Cassini captured the images that compose this animation on August 20, 2009. At present, Prometheus (the inner shepherd of the F ring) and the F ring collide with every orbit of Prometheus around Saturn. Prometheus dips into the F ring, causing a gore and pulling out a streamer of material. On the next orbit, Prometheus dips into the F ring ahead of its previous position. The result is a series of gores that slowly get sheared out as a result of the differential rates that the ring particles orbit Saturn (objects closer to Saturn complete one orbit in a shorter period of time than objects farther from Saturn). Pandora, the outer shepherd of the F ring, is also visible in this animation. The moons are lit from below by the Sun and from above by Saturnshine.

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
Read more articles by Emily Lakdawalla

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