Cassini: 10 years and counting

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Oct. 15 2007 9:36 AM

Cassini: 10 years and counting

Has it really been 10 years since the launch of the Cassini Saturn probe?


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!  


To celebrate the anniversary, NASA has released a whole bunch of cool images and animations. They're all incredibly beautiful, but how can you resist this one in particular?

[Click the images for much larger versions!]

There's something about seeing Saturn from a height. Wow again.

I'm also fond of this one:

See the rainbow? In this image, the Sun is directly behind the camera. The sunlight hits the ice particles in the rings and gets refracted back toward you, making a bright spot in the rings. But why the rainbow? At first I thought it was a glory, but actually it's an illusion! Cassini doesn't take color images like your digital camera does. It takes a series of images with different filters which are then combined on the ground to produce color. As Cassini swept past this point over the rings, it took three images (red, green, and blue) which were then added together. Since Cassini was moving, the spot smeared out, and since the color images were taken sequentially, we see an elongated rainbow. We can also see yellow and other colors in the rainbow because the spot was big, bigger than the amount it got smeared out by Cassini's motion. The right part of the spot in one image overlaps the location of the left part of the spot in the next image, so the primary RGB colors add together to get the secondary colors.


This next one is incredible. It's an animation of tiny Prometheus and its effect on Saturn's thin F ring:

[To see this better, click the animation for a larger version.] Prometheus orbits Saturn every 14.7 hours in an ellipse. The top of the ellipse brings it just out to the orbit of the F ring particles. When it gets close, it pulls out a streamer of material. The camera stays centered on the moon, but the overall orbital motion of Prometheus and the ring is to the right. Prometheus, closer to Saturn, moves a little bit faster than the ring particles. As it pulls out the streamer of particles, they fall toward the moon and wind up orbiting Saturn a little faster than they did before. However, they still aren't moving as quickly as Prometheus, and fall back to the left as the moon leaves them behind. The view is odd since the moon stays centered; if the point of view of the camera were stationary and everything swept past from left to right, it would look different. You'd see the actual elliptical motion of the moon as a big arc from left to right, and the ring particles would be seen moving that direction as well, just not as quickly as the moon does.

It all depends on your POV.

And that, BABloggees, is the whole point. We don't go to these exotic locations in the solar system because we know everything that's going on, or because we know what we'll expect to see. We go because we don't know. But we also go because we need to have our positions rattled, our notions shaken, our ideas tested. When we see Saturn from above, or co-orbit with a moon, or see a rainbow reflected in particles of ice a billion kilometers away, the only thing we can be sure of is that we'll see new things, unexpected things.

That's how we learn. That's how we grow. And that's what science does for us.


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