This morning, I wrote about some pictures of Saturn’s moon Enceladus I found rummaging through NASA’s Cassini raw images archive. Enceladus is a small icy moon that may have an ocean of liquid water under its surface. It’s a fascinating world, and is one of those objects that cannot seem to take a bad picture; every shot of it is dramatic and intriguing.

Even so, as I clicked through the raw images from the distant spacecraft, I got a jolt when I stumbled on a series of pictures depicting the tiny disk of Enceladus with the gigantic visage of Titan sliding past! I quickly grabbed the images and made a short animation showing the scene, with a description:

[It helps to watch full-screen and in hi-res; I recorded it in 1080p. The images from Cassini look pretty good that way.]

Nifty, eh? I’ll note that in between some of the frames of the animation Cassini was programmed to change filters. That’s most obvious by looking at Titan itself; when the blue filter was used the atmospheric layers become more obvious — an upper level haze layer is dark in blue colors. Here’s one of those images using the blue filter:

You might wonder why the picture isn’t blue if a blue filter was used. (more…)

Take four moons, some rings, a schoolbus-sized spacecraft, and mix them together. What do you get?

Magnificence.

That stunning shot is from the Cassini spacecraft orbiting Saturn. The big moon is Titan, and by big, I mean bigger than the planet Mercury. Big enough to have a thick nitrogen atmosphere, clearly visible in this picture. The bright moon superposed right on top of Titan is Dione, its icy surface shiny and white.

On the right, just outside the rings, is tiny, flying saucer-shaped Pandora. And the fourth moon? That’s Pan, the tiny white spot in the gap in the rings on the left, barely visible in this shot. But that’s understandable, since Pan is less than 30 km (18 miles) across, and this was taken from a distance of nearly 2 million kilometers (1.2 million miles) away!

I love pictures like this; they remind me that even after 7 years of Cassini touring around Saturn, there’s still much to see and much beauty to behold there.

Image credit: NASA/JPL-Caltech/SSI

I know I just posted a global color map of Saturn’s moon Titan, but sometimes it’s cool just to take a step back and look at a picture that gives a little context… and it doesn’t hurt that it’s a moody grayscale shot, too:

[Click to encronosenate.]

This shot of Titan was taken by the Cassini spacecraft back in August, and shows the moon superposed on Saturn’s rings, seen here almost — but not quite — edge-on.

The fact that you can see surface detail on Titan is a dead giveaway this shot was taken in the infrared: optical light, the kind we see, can’t penetrate the thick, hazy, nitrogen/methane atmosphere blanketing this moon. Infrared light gets through, though, so surface features can be seen. In fact, this image was taken using a filter that lets through light at 938 nanometers (the reddest light the human eye can see is about 750 nm). Methane is pretty good at absorbing light at a bunch of different wavelengths, but at 938 nm it’s transparent, so this is a particularly good place in the spectrum to look at Titan — astronomers call it the "methane window". Not only that, but this image also employed a polarizing filter, which blocks a lot of light from the atmospheric haze, making the surface easier to see (it also makes rainbows appear and disappear, too).

Not that the atmosphere is completely invisible in this picture: look around the moon’s edge and you can just see some of the upper atmospheric layers, and at the top you can easily spot the north polar hood, which may have water ice crystals in it.

And that dark region on Titan’s surface? It may have once been the bed of a methane sea, but now it’s a dry, vast area of wind-blown dunes, hydrocarbon grains collected by the Titanian winds. It’s called Shangri-La, and that makes me smile. I’m not sure anything at -180°C could be called a human paradise, but for astronomers, it’s certainly a scientific one.

We’ve sent space probes to every planet in our solar system (and if you’re a die-hard Pluto fan, you only have to wait 4 more years). And yet there is still much to see, much to explore. Not every world gives up its secrets easily, and perhaps none has been so difficult to probe than Titan, Saturn’s largest moon. Bigger than Mercury, second only to Jupiter’s Ganymede, Titan has an atmosphere of nitrogen so thick it has twice the Earth’s air pressure at its surface.

That thick, hazy atmosphere is impenetrable by optical light… but infrared light can pierce that veil, and the Cassini space probe is well-equipped with detectors that can see in that part of that spectrum. And after 7 years, and 78 fly-by passes of the huge moon, there are enough images for scientists to make this amazing global map:

Pretty awesome. And making this animation was a huge effort. First, not all of the passes were at the same distance, so scientists had to resize the images to match the scale. Cassini passed at different times of day for the local regions, so the sunlight angle changed, making illumination and shadowing different. The atmosphere of Titan is dynamic, changing with time, so again compensations must be made. It’s painstaking work, but the results are truly incredible:
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When digital imagery in astronomy came along about 25 years ago, I knew right away it would change everything, but one thing I didn’t expect was the advent of citizen science. Spacecraft and observatories store their images on hard drives, and anyone with access and the knowledge of how to process that data — no simple task, I assure you! — can use it to do their own work.

It also means smart, talented people can take that data and put it together to make stunning pictures of space that otherwise may never see the light of day. Gordan Ugarkovic is one of these people. He’s a Croatian software developer, but in his spare time takes data from spacecraft and makes simply devastating portraits from them. Like this one of Saturn’s moons Tethys and Titan as seen by Cassini:

[Click to enchronosenate.]

Didn’t I see this in Star Wars? And here I thought Mimas was the Death Star moon^*.

Anyway, the detail is stunning in his original high-res version. You can see craters on Tethys, and the thick atmosphere enshrouding Titan (including the north polar haze cap). The image is very close to natural color, so this is approximately what you would see if you were there (shortly before freezing and asphyxiating, but what a way to go).

Gordan has done many, many such images, including this moody shot of Titan and Rhea, and this simply incredible wide-angle shot of Titan and background stars shown inset here (click it to embiggen, and trust me, it’s awesome).

Wanna give this a try? Raw Cassini images are stored online, but it’s not as simple as you might think. Still, you might have fun, and Emily Lakdawalla from The Planetary Society Blog (who does this herself as well) pointed out to me that this Web interface has raw data from Cassini, Galileo, and Voyager, and more missions other missions are online too.

In general, there are so many images from these spacecraft that the scientists on the teams themselves don’t have time to look them all over. It’s entirely possible you’ll find something new and interesting. If you do, make sure you check out the Unmanned Spaceflight forum, which has loads of space enthusiasts who spend a lot of time working on this stuff. I go there fairly often to see what’s new, and you should too.

Image credit: NASA/JPL/Space Science Institute/Gordan Ugarkovic (used with his permission)

^* The first person to leave a comment saying "That’s no moon" will get a light saber up their Tauntaun.

Like any scientist, I love a good mystery. Sometimes it’s fun when they are long, complicated, involve subtle and difficult layers, and require a vast effort to unravel.

And sometimes it’s cool when they are simply stated and simply solved. Like asking "Where does the water in Saturn’s upper atmosphere come from?" and finding out the answer is "It rains down from the moon Enceladus."

Water has been seen deep in Saturn’s atmosphere before, but a few years back it was detected in the upper atmosphere as well, and that’s a bit weird; there don’t appear to be any ways to get it from deep down in Saturn to the top parts of its clouds. So how did it get there?

Well, the tiny, icy moon Enceladus was discovered to have geysers at its south pole, actively spewing out quite a bit of water into space. Most of it goes into space and is gone forever. Some actually forms a ring around Saturn called the E-ring, and some no doubt hits other moons. Generally, when a moon blasts stuff into space (like Jupiter’s moon Io does with its sulfur volcanoes) the material forms a big donut-shaped region around the planet. It was figured that Enceladus was doing the same thing with water around Saturn, but even the Cassini spacecraft, which is right there, couldn’t detect it. It’s pretty hard to sample.

But astronomers used Herschel, an Earth-orbiting infrared observatory, to observe Saturn. They found a peculiar feature in the infrared spectrum of Saturn, and realized it’s from this Enceladusian water torus. Apparently, about 3-5% of the water from Enceladus’s geysers falls on Saturn, literally raining down in sufficient quantities to explain the presence of the water detected in the ringed planet’s upper atmosphere.

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