Cassini's pentaverate

The entire universe in blog form
June 2 2011 9:30 AM

Cassini's pentaverate

I haven't posted a Cassini picture in quite some time. To make up for that, here's a stunner of a family portrait showing five worlds!

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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[Click to enchronosate.]

This shot shows Saturn's rings nearly edge-on, but dominating the scene is Rhea, 1500 km (950 miles) in diameter, seen here 61,000 km (38,000 miles) distant. Below it is Dione, to the right and just above the rings is Epimetheus, and Tethys is all the way on the right, below the rings.

So what's the fifth moon? Look to the right of Dione, right at the rings. See that tiny bump? That's dinky Prometheus, all of 119 km (71 miles) along its longest dimension -- it's basically a spud orbiting Saturn. Prometheus, along with its sister moon Pandora, act like shepherds, keeping Saturn's F-ring particles entrained.

Saturn is a weird, weird place, and it's orbited by a diverse collection of weird, weird moons. I forget that sometimes, but images like this really drive it home.

... on the other hand, as we discover more planets orbiting other stars, we see lots of them with masses like Saturn's. Of course, low-mass planets like Earth are much harder to find, but still. Who knows? It may turn out Saturn's normal, and we're the weird ones.



... and if you're wondering about the post title, this may help. Whoa, man.



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