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SYFY WIRE Bad Astronomy

Desktop Project Part 10: The crescent and the plume

By Phil Plait

[Over the past few weeks, I've collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. Sometimes I was too busy, sometimes too lazy, sometimes they just fell by the wayside... but I decided my computer's desktop was getting cluttered, and I'll never clean it up without some sort of incentive. I've therefore made a pact with myself to post one of the pictures with an abbreviated description every day until they're gone, thus cleaning up my desktop, showing you neat and/or beautiful pictures, and making me feel better about my work habits. Enjoy.]

With planetary pictures, angle is everything. If you have your back to the Sun and face your target, it's fully lit, and looks like a disk. But if you go around to the other side, and put your target between you and the Sun, it becomes a crescent. Get the angle just right, and that crescent gets very thin...

... which is a view of Saturn's moon Enceladus we can never get from Earth, but one that the Cassini spacecraft gets all the time. And it's way, way cool:

[Click to encronosenate.]

But there's an added bonus here, one that makes this picture that much more amazing: that fuzz at the bottom? Those are enormous geysers, towering sprays of water blasting out of cracks in the surface of the moon and reaching upward for hundreds of kilometers!

We've seen the geysers before, and in fact Cassini has flown through them to find out what they're made of (turns out water laced with lots of organic goodness like acetylene, formaldehyde, and much more). They're very dim, but easy to see when backlit by the Sun like this.

So we know Enceladus must have liquid water under its surface, to feed these geysers. But is it local, like a subsurface lake, or is the ice of the moon floating on a global ocean? New studies of the cracks from which the geysers emanate seem to indicate the water is everywhere! The geysers are formed from gravitational stress when the moon nears Saturn in its orbit, and the size and shape of the cracks really make it look like the water source is a global ocean, like Jupiter's moon Europa.

Isn't that amazing? We can learn a lot about a tiny, icy, backlit world, just by tasting its water.

Image credit: NASA/JPL-Caltech/Space Science Institute

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- Lifeâs cauldron may be bubbling underneath Enceladus
- Enceladus!
- Enceladus does and does not have a global ocean

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