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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I spent all day yesterday writing a 2000-word article for a print venue to be named later, and the weather outside is sunny and delightful and begging to be biked in, so I am disinclined to write something deep and philosophical today. So instead here is just a simply way-cool picture from Cassini taken in 2009, showing the Saturnian moon Rhea peeking out from behind the much larger Titan:

[Click to eneldergodenate.]

[UPDATE: I messed up here. In the original post I misread Titan's radius when I looked it up, and was comparing it to Rhea's diameter. This changes my numbers enough that I have simply corrected everything below; otherwise it would be too confusing to read. Thanks to the commenters for pointing this out!]

Rhea is a little over 1500 km (900 miles) across, and Titan 5150 km (3100 miles). However, in this shot, Rhea was almost two and a half times farther away than her big sister, so it looks smaller than it really is. Titan has a thick atmosphere, which is pretty obvious in the picture, while Rhea is basically a ginormous iceball.

Still, hmmm. Titan and Rhea are the two largest moons of Saturn, but to be honest Titan really is a lot bigger than Rhea, more than 3 times wider. Why such a big gap in sizes? Jupiter’s two largest moons, Ganymede and Callisto, are much closer together in size (5260 and 4820 km, respectively), and Ganymede is only 1.7 times bigger than Jupiter’s fourth largest moon, Europa. After that, though the rest are far smaller.

It seems to me that Saturn and Jupiter are telling us something about the physics of the way their moons formed. But what could it be? Titan orbits well over twice as far from Saturn as Rhea, while Ganymede is actually closer to Jupiter than Callisto. Is that important? Did those moons form at other distances and get their orbits jostled through gravitational interactions over billions of years, maybe even switching positions?

These are pretty basic questions, but it’s questions like these that lead to basic insights on how our solar system formed and changed as time went on.

And dangit! I guess I did get a little deep and philosophical here. Ah well, what can I say? Images like this are so pretty and so interesting to look at, they spark all kinds of thought processes in my head. And the more I do that, the more I want to do that. Science is like that: addictive, but in a good way.

Damn! Did it again.

Image Credit: NASA/JPL/Space Science Institute

A quirk of physics can lead to some real drama. Two quirks of physics can lead to very dramatic pictures.

"Why Phil, what could you possibly mean?", I hear you thinking^*.

This is what I mean: Saturn’s moon Titan, sliced in twain by the planet’s rings:

[Click to enchronosenate.]

Due to a quirk of physics (aha!) all the moons and rings of Saturn orbit the big planet in the same plane. There are two reasons for this: one is that they almost all formed out of the same disk of material orbiting the Sun. As the pieces clumped together, they naturally all stuck to the same plane. A second reason is that any object that tries to stray out of that plane (or that gets captured by Saturn like some of its bizarre outer moons) feels a torque on it, forcing it back down. That torque is provided by Saturn itself, which has tides that tend to circularize and flatten all the orbits of the moons, confining them to the planet’s equatorial plane. The physics of this is a little hairy, but I do have a simplified explanation using the Earth and Moon as an example.

The Cassini spacecraft orbits Saturn, but it has rockets on board that can push it around into any orbit the engineers and scientists back home want. That usually means a tilted path, plunging it through the equatorial plane twice each orbit. When it is precisely in that plane it sees the rings edge-on, and if the geometry is right it can spot one or more moons.

In this case, the gigantic moon Titan was in its sights, and the angle was such that the rings slice right across it.

Titan is so big it has a substantial atmosphere, murky and thick, which hides its surface. So why do we see details on the moon in this picture?

Due to a second quirk of physics (aha aha) infrared light can penetrate Titan’s soupy air. Different surface features (like lakes of liquid methane and ethane!) emit and reflect different amounts of IR light, and that goes up through the clouds and into Cassini’s detectors, which were cleverly designed to detect that specific wavelength of light.

And that, you see, is how some nifty physics can provide you with a very dramatic picture. Well, that and a few hundred million dollars, a team of very smart people, and a decade or two to design, build, and get your spacecraft to its target.

… which, again, involves an awful lot of physics. So really, if you want to see just how spectacular and awesome the universe is, science is the way to go. We deliver.

Image credit: Credit: NASA/JPL/Space Science Institute

^* All professional bloggers can read minds. It’s how we know exactly what to say to tick off the largest fraction of our readers.

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