Seasons E-rings!

Bad Astronomy
The entire universe in blog form
Dec. 26 2009 7:58 AM

Seasons E-rings!

[It was either that title or "E-ring in the New Year".]

Here's an unusual shot from the Cassini spacecraft: Saturn's faint, diffuse E ring, seen almost edge-on:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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I like this picture! First, we're used to seeing Saturn's rings looking sharp and well-defined, but this ring is fuzzy. It's huge; it doesn't even start until well outside the main rings, about 130,000 km (78,000 miles) above Saturn's cloud tops, and is 300,000 km (180,000 miles) across! It's thought that the ice particles in the ring are supplied by geysers from the moon Enceladus.

Second, we're also used to seeing pictures of Saturn sitting in inky darkness. Saturn, its rings, and most of its moons are very bright, far brighter than the background stars. Exposing the images correctly for Saturn means the stars don't show up, so the background is black (though not always, as this nice shot of the Pleaides from Cassini attests). But the E-ring is so faint that a longer exposure was needed, and then the fainter stars show up in multitudes.

This image was taken when Cassini was 2.5 million km (1.5 million miles) from Saturn, which was far enough to fit in a good amount of the edge of the ring. I really love all the images Cassini takes, but it's the more unusual ones I really enjoy. Here's hoping we see lots more in 2010!

Image credit: NASA/JPL/Space Science Institute