October 20, 2017

22.04.10-The Exotic World of Prometheus.

(Credit: NASA/ESA/Cassini).

(Credit: NASA/ESA/Cassini).

 The tiny shepherd world of Prometheus.

    The moons of Saturn continue to astound. The count now stands at 61, and one by one, NASA’s Cassini orbiter is giving us a close up look at these unique worlds, some for the first time. Last year, Cassini passed within 36,000 miles of Prometheus just the day after Christmas. Discovered by Voyager 1 in 1980, this shepherd moon dips within the F-ring once every 15 hour orbit. This fact is apparent as the oblong cratered surface on the 74 mile long moon is coated with a fine layer of dust, giving it a smooth appearance. The constant “plowing” of these moons through Saturn’s rings cause the grooves that we see, and also confines the F-ring. These images are especially satisfying to Carolyn Porco, lead scientist of the Cassini research team who was also on hand for the tiny moon’s initial discovery by Voyager in 1980. It’s likely that we won’t get another look at this bizarre shepherd moon for some years to come!

31.08.09: An Edge on Saturn.

A rather odd event is transpiring in the Saturnian system, one that only happens a couple of times in our lifetime; its rings are vanishing. Not really, of course; we are merely passing through the super-fine ring plane as viewed from the Earth. The exact date of the “crossing” as viewed from Earth is Friday, September 4th, when the 20 meter thick rings will be exactly edge on and vanish from all but the largest telescopes. Just a few weeks ago, Saturn passed equinox, when the rings were edge on to the Sun and hence, not illuminated across their 100,000+ km expanse. This happens every 14 to 15 years during the planet’s 29.7 year orbit.

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