Tag: Titan

Saturn eclipses an icy moon

By Phil Plait | July 18, 2012 7:00 am

The mighty planet Saturn is circled by a fleet of moons, each as different from the other as individual people. And as weird and alien as it seems, this Saturnian system of planet and moons have some similarities to our own Earth and Moon. For example, as they orbit Saturn, the moons can be eclipsed by it when they pass behind the planet and into its shadow.

The Cassini spacecraft caught exactly this event as the icy moon Enceladus slipped into Saturn’s shadow last October… and there’s more here than might initially meet the eye:

That’s amazing [click to penumbrenate]. But it may not be obvious what you’re seeing at first! Enceladus is the moon to the upper left. It’s about 500 kilometers (330 miles) across, and its surface is almost entirely water ice. At the time this shot was taken, it was about 26,000 km (16,000 miles) from Cassini.

If the moon were just sitting out there, half of it would be lit by the Sun, and half would be in darkness. Cassini was off to the side a bit when this was taken, so we see the hemisphere that is almost entirely lit by the Sun. The day/night line – called the terminator – runs from the upper left to lower right of the moon on its left side as seen here.

But because Enceladus was partially into Saturn’s shadow, the sunlit side of the moon that would normally be painfully bright is dusky and dark. The shadow is deepest toward the bottom of the moon. The geometry of this scene depends on so many angles! The terminator line, the position of Cassini relative to the moon and Sun, the position of Saturn, and even the curve of the planet itself as its shadow envelops the moon.

And we’re not done. Photobombing the scene at the lower right is the monster moon Titan, which is 10 times bigger in diameter than Enceladus! But it was over a million kilometers away from Cassini when this picture was taken, so it actually looks smaller than its very much smaller sibling. It appears dark, even compared to the shadowed Enceladus, because Titan only reflects about 1/5th of the light that hits it, while shinier Enceladus reflects almost all the light that impinges on its icy surface.

Funny, too: the edge of Titan looks fuzzy, because it has a thick atmosphere. Enceladus has no atmosphere, but still looks a bit fuzzy as well due to Saturn’s shadow: the planet does have an atmosphere, so the shadow itself isn’t sharp.

The complexities of understanding even a seemingly simple picture are ridiculous when that picture comes from Saturn. But that’s so often true: things do appear easy at first glance, but far more complicated when you peer more deeply. The Universe, as are human affairs, is rarely so black-and-white.

Image credit: NASA/JPL-Caltech/Space Science Institute

Related Posts:

- The more distant moon
- A shadow falls on the ice geysers of Enceladus
- Midnight on a ringed world
- Titan’s shadow

Titanic antarctic vortex antics

By Phil Plait | July 11, 2012 6:22 am

The Cassini spacecraft has been orbiting Saturn since late 2004, and has spent most of that time more or less in the same plane as the rings and moons. That allows it to pass close to these interesting places and see them in high resolution.

But scientists and engineers recently changed that, flinging the probe into a more inclined orbit so that it can see things from a different vantage point, literally getting a new perspective on them. For example, from this tipped path, it was able to clearly see the south pole of Titan, Saturn’s ginormous moon – the biggest in the soar system, bigger than the planet Mercury! And what it saw surprised everyone, and for good reason:

Isn’t that weird looking? Like some kind of bacterium, or a cell. In fact, it is a cell, but not the biological kind. It’s an air cell, a vortex, a spinning around the pole. Titan has a thick atmosphere (thicker than Earth’s in fact) and it moves. This cell of air rotates once every 9 hours or so, far faster than Titan’s own 16 day spin. Cassini took enough images to make this animation of the vortex’s motion:

Things like this are seen at the poles of other words; Saturn itself has one, as does Venus. Titan also has a "hood" a haze layer over its north pole. That may be a seasonal feature, and right now winter is coming for Titan’s southern hemisphere*. Perhaps this vortex plays a part in forming the polar hood, and we’ll see one over the south pole soon.

That’s not clear yet, but it may become so as Cassini continues to investigate this incredible system. It’s been there for almost 8 years, and we’ve barely scratched the surface of what’s going on. There’s a whole lot of real estate in the Saturn system, and it changes all the time. We could use 50 Cassinis stationed there, and it still wouldn’t be enough to gather up all the beauty and amazing slices of nature to be seen.

Credits: Video: NASA/JPL-Caltech/Space Science Institute; Music: “Passing Action” by Kevin MacLeod

* Hodor!

Related Posts:

- The look of a Titanic moon
- Your Cassini awesomeness for today
- A window into Titan
- Watch out Titan! Vader’s onto you!

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Cassini, Saturn, Titan, vortex

Ice moon, ghost moon

By Phil Plait | May 10, 2012 8:55 am

One of my favorite things to do is take a gorgeous astronomical image and pierce down into it, finding some detail not discussed in press releases and other articles.

On the other hand, sometimes I’ll post a picture because it’s so, so cool:

[Click to encronosenate.]

That’s a shot of Saturn’s rings and moons by the Cassini spacecraft, taken in mid-April 2012. Cassini was nearly in the same plane as the rings, so they look like a knife cutting across the image. The bright moon is Enceladus, tiny and icy, almost but not quite full as seen from this angle.

But the scene stealer is Titan, the moon as big as a planet — bigger than Mercury, actually — looming in the background, nearly invisible. This image, taken using a filter that only lets through green light, shows just how much darker Titan is than Enceladus. The bigger moon is shrouded in a thick, hazy atmosphere, and reflects about 1/5th of the sunlight that falls on it. Enceladus, on the other hand, is covered in ice, and reflects nearly all the light that falls on it. So the brightness ratio you see here is real: Titan really is far darker then Enceladus.

… and there you go. I drilled down a bit into the picture’s science anyway. I guess I had to. It’s in my nature; when it comes to science, I’m reflective too.

Image credit: NASA/JPL-Caltech/Space Science Institute

Related Posts:

- An icy Titanic encounter
- Enceladus fires on Alderaan
- Incredible quadruple transit on Saturn!
- The scale of Saturn

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Q&BA: Which moon has the best chance for life?

By Phil Plait | April 20, 2012 10:04 am

Every weekend when I can I do an interactive live video chat on Google+ where people can ask me questions about space and astronomy. I call it Q&BA, and it’s always fun to hear what questions are on people’s minds.

Apropos of my recent post about Saturn’s moon Enceladus, I got this question: "Which moon has the best chance for life: Titan, Europa, or Enceladus?" This is a common question, and worth exploring! Here’s what I said:

Mars is still an interesting place to look for life, but those moons — all three — are very, very enticing. I’d love to see us launching future space probes with some icy targets in their sights.

[P.S. The aspect ratio of the video is stretchy for some reason; the video looked fine before I uploaded it to YouTube. I'll try to track this problem down.]

I have an archive of Q&BA links and videos. Take a look and see if there are other ones that tickle your imagination.

Related Posts:

- Q&BA: Can we build a space habitat?
- Q&BA: The Science of Science Fiction
- Q&BA: How does a gravity slingshot work?
- Q&BA: Why spend money on NASA?
- Q&BA: What happens if you are exposed to the vacuum of space?

CATEGORIZED UNDER: Astronomy, Piece of mind, Q & BA, Space
MORE ABOUT: Enceladus, Europa, life, moons, Titan

The look of a Titanic moon

By Phil Plait | April 12, 2012 9:30 am

Astronomical imaging is an interesting process. The most common question I get when I show a picture is, "Is this what it would look like if you were actually there?"

That’s a tough question to answer in many cases, because our eyes see in a different way than cameras take pictures. We have receptors in our eyes that are sensitive to red, green, or blue light, and they send signals to the brain which then constructs a "true color" image from that. In astronomy, we use filters to mimic that, but they don’t actually perfectly represent the way our eyes see. And even after you get the picture, there are adjustments in contrast, brightness, and so on that can alter a photo.

A few months ago, the folks at Cassini released a really cool picture of Saturn’s moon Titan. It’s a great shot, have no doubt, but amateur astrophotographer Gordon Ugarkovic — who has some experience putting together color pictures from Cassini images — felt that processing the image in a different way might represent natural color better. So he reprocessed it, producing this amazing image:

[Click to encronosenate.]

All by itself, that’s a stunning shot. Titan is larger than Mercury, but still dwarfed by the gigantic planet it orbits. Titan has a thick atmosphere, and you can see some details in it, like the "polar hood" over its north pole. Also, a really neat effect is on Saturn itself. You can see the rings, as well as the shadow of the rings on Saturn’s cloud tops (below the rings themselves). Near the edge of Saturn, the shadow dips downward, hooking down a bit. That’s a product of several effects, including refraction; the bending of light as it passes through the atmosphere (similar to why a spoon looks bent in a glass of water).

It’s interesting to compare Gordon’s version to the one released by Cassini as well (shown here; click to embiggen). Both are beautiful, interesting, and show a lot of detail. The "official" release is darker, a bit, which is the most obvious aspect. Gordon’s shows details in Titan’s polar hood better, but I see more subtle variations in Titan’s atmosphere overall in the official shot, and perhaps better detail in the ring shadows, too.

So which one is better? Neither! They both are amazing, and show slightly different things. One might appeal to you more in an aesthetic sense, or in a scientific sense, or because you’d rather see details in Titan versus Saturn, or whatever. But in my opinion, it’s OK to like both or neither or one over the other for whatever reason you prefer.

In astronomical imaging — something I did professionally for over a decade — the image is never really what you’d see if you were there, because the instant you use a camera and a telescope you’re already two steps removed from real vision. You can try to get as close to what the human eye would see as you can, but I think in most cases that’s a conceit, something that’s interesting to our minds but perhaps not our eye.

And like all photography, this is art. If you want to display an astronomical object and are being true to what you are showing, then it’s OK. These images done for press releases or simply for their own sake are meant to inspire our imagination, fire up our curiosity, and see their beauty.

Beauty that is, at the very least, in the mind’s eye of the beholder.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Worlds bigger than worlds

By Phil Plait | March 1, 2012 7:00 am

Because I love each and every one of you, here is a fantastic portrait of two worlds: Saturn and its ginormous moon Titan, courtesy of the Cassini spacecraft:

Isn’t that breathtaking? [Click to encronosenate.]

I love the panoply of shadows from the rings on the cloud tops of the gas giant planet, clearly showing Saturn has not one big ring, but thousands of thin ringlets. You can also see subtle patterns in the clouds as well. If you look very closely, you’ll see the shadow of the moon Prometheus on the left just below the ring shadows — the moon itself is the white speck just above the rings to the right, just to the right of Saturn’s limb — as well as the shadow of the moon Pandora on the right below the rings. Pandora itself is well outside the frame of this shot though.

Of course, fuzzy Titan looms of the planet’s edge on the right as well. Titan is huge, bigger than Mercury, and if Saturn weren’t there might be considered a planet in its own right. But definitions aside, Titan is a varied and complex place, worthy of intense study. It has weather, lakes of liquid methane, dunes blown and sculpted by wind, and boulders made of water ice harder then rock is on Earth.

Who wouldn’t want to take a closer look at a world like that?

Image credit: NASA/JPL-Caltech/Space Science Institute

Related Posts:

- The scale of Saturn
- A window into Titan
- Titanic slice
- An icy Titanic encounter

CATEGORIZED UNDER: Astronomy, Pretty pictures

Top 14 Solar System Pictures of 2011

By Phil Plait | December 8, 2011 6:30 am
Top 14 Solar System Pictures of 2011
A flower on the Moon
The Earth takes a bite out of the Sun
Dawn of a new vesta
Earth's lumpy gravity
The Extraordinary face of the Moon
The Sun's starting to get feisty
A hole in Mars
The last planet
MESSENGER's Mercury rising
A storm on Saturn eats its own tail
A solar system family portrait from the inside out
Solar Menagerie, real and fantastic
A hidden world revealed
Water world

An icy Titanic encounter

By Phil Plait | November 8, 2011 11:30 am

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. Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Cassini, Enceladus, Saturn, Titan

A panoply of moons and rings

By Phil Plait | October 24, 2011 4:43 pm

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


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

Related posts:

- A trillion and five moons
- Cassini’s pentaverate
- The bringer of fire, hiding in the rings
- Cassini’s slant on the rings

CATEGORIZED UNDER: Pretty pictures

A window into Titan

By Phil Plait | October 14, 2011 10:35 am

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.

Related posts:

- Polarized rainbow, what does this mean???
- In astronomy, a polarizing view is good
- Watch out, Titan! Vader’s onto you!
- A hidden world revealed: Titan

CATEGORIZED UNDER: Astronomy, Pretty pictures

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