So on Twitter, my pal Carolyn Porco — imaging team leader for the phenomenal Cassini Saturn spacecraft — announced that a bunch of raw (that is, unprocessed) images were just released from Cassini. Taken on April 14, these new shots show the moons Tethys and Enceladus. I’ve written about Enceladus about thirty two bajillion times, because it’s fascinating, and photogenic as heck. Geysers of water are erupting from its south pole, reaching heights of hundreds of kilometers, with some particles leaving the tiny moon altogether.
And, unsurprisingly, the new pictures do not disappoint, especially this one of Enceladus!
I know. [Click to encronosenate.]
It almost looks like a solar eclipse picture, but the dark circle is actually the night side of Enceladus, with the sunlight coming from the lower left. You can see quite a few geyser plumes, blasting up from the surface to such heights that they’re illuminated by the Sun and we can see them around the edge of the moon.
As I looked at this shot, I suddenly realized something neat: you can see (at least) three dark arcs across the geysers — I’ve used arrows to point them out in the inset picture. These arcs are actually shadows being cast by the moon itself! The curved edge of the moon’s horizon casts a shadow into space, and where it falls across the geyser plumes it reveals itself as a dark, curved line.
What’s so very cool is that you can see the arc of the shadow edge on the upper left — what I’ll call the first arc — is actually higher off the limb of the moon than the one lower on the right (the third one is closer to the limb of the moon under the first arc).
Why is this cool? Because it tells us where those shadows are falling on the geysers. In other words, it’s 3D info on the geysers for free!
[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
This may be my favorite picture of Saturn’s moon Enceladus yet:
Quick! It’s trying to get away!
My first thought (well, my real first thought was that this is Enceladus on full afterburners) was that this was a composite: two images combined. The moon is icy and very bright, while the plumes of water shooting away from cracks in its surface are faint. But actually, there are two separate light sources here! The face of the Moon we see here is being lit by a full Saturn (think of Saturn as being behind you as you look at the picture). But the Sun is behind Enceladus (not directly behind, but mostly behind and off to the side of the picture), and is illuminating the geysers. That’s why the fainter plumes are visible; we’re looking at the dark side of the moon! If Saturn weren’t lighting it up, the moon would look much darker, and the plumes would be even more visible.
I love how the plumes look like a rocket exhaust. With the moon itself just a little offset in the picture, a little above the center, our brains make it look like it’s jetting up, up, and away!
But don’t worry about it actually rocketing into the wild black yonder. Read More