Tag: Enceladus

Angling in on Saturn

By Phil Plait | September 25, 2012 7:04 am

Pretty much every picture of Saturn sent back home from the Cassini spacecraft is devastatingly gorgeous, but it’s confession time: I prefer the greyscale ones to the pictures in color.

Why? Because this:

Holy ringed gas giant awesomeness! [Click to encronosenate.]

This shot was taken earlier this year, in June, when Cassini was about 3 million kilometers from the planet. Saturn has a thick haze above its cloud tops, obscuring much of the details of the clouds below (one of the main reasons it doesn’t sport the same spectacular cloud bands as its big brother Jupiter), but this image was taken using a near-infrared filter – just outside the normal range of human vision (centered at 752 nanometers, for those who want details) – that can see some light that gets through the haze. The white spots and elongated features are the tops of clouds of ammonia, some of which are thousands and even tens of thousands of kilometers long.

I love the angle on this picture. Cassini was south of Saturn’s equator, looking north. The northern hemisphere of the planet is edging toward summer right now, so the Sun is shining down on the rings, projecting their shadow on the southern hemisphere. We see the rings here from the unlit side, so they look a bit darker than you might be used to. However, since they’re made almost entirely of water ice, they’re transparent and scatter sunlight, so you can see them even from their shadowed side.

As a bonus, you can also see the tiny moon Enceladus on the lower left. Of course, when I say "tiny", I mean the size of my home state of Colorado.

This picture is jaw-droppingly beautiful, and I think a big part of that is that it’s greyscale (what some people call "black and white", which isn’t accurate since we see lots of shades of grey). While color images can be stunning, there is something about the contrast and chocolaty smoothness of greyscale that makes pictures like this more magnificent, more dramatic, and more brooding. I don’t know what it is – it’s the same phenomenon that happens with old movies, too – but for me it’s certainly a powerful effect.

As if Saturn needs any help.

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

Related Posts:

- The scale of Saturn (and The Scale of Saturn, redux)
- Ice moon, ghost moon
- Saturn broods while a storm dissipates
- A shadow falls on the ice geysers of Enceladus

CATEGORIZED UNDER: Astronomy, Pretty pictures

When will we find life in space?

By Phil Plait | August 23, 2012 6:51 am

[The article below was originally posted on the BBC Future blog, and was titled "Will we ever… find life elsewhere in the universe?" I'm reposting it here because, oddly, the BBC page is only readable for people outside the UK! It has to do with the BBC rights and all that. But they gave me permission to post it here, and since I thought it was fun and provocative, I figure y'all would like it. Enjoy.]

Will we ever… find life in space?

One of the reasons I love astronomy is that it doesn’t flinch from the big questions. And one of the biggest is: are we alone?

Another reason I love astronomy: it has a good shot at answering this question.

Even a few decades ago hard-headed realists pooh-poohed the idea of aliens. But times change, and so does science. We’ve accumulated enough data that makes the question less far-fetched than it once was, and I’m starting to think that the question isn’t "Will we find life?" but rather "Which method will find it first?"

There are three methods that, to me, are the front-runners for finding life on other worlds. And I have an idea as to which one may find it first.

Life on Mars?

The first method follows the principle that when you’re looking for something, it’s best to start close to home.
We know of one planet that has life: Earth. So it makes sense to look for other places with Earth-like conditions: that is, liquid water, oxygen in the air, nutrients for growth, and so on.

The most obvious place to look is Mars. At first glance it appears dry, cold and dead. But if you can see past that, things start to look up. The polar caps, for example, have lots of frozen water, and we’ve directly seen ice at lower latitudes on the Red Planet as well – meteorite impacts have left behind shiny craters, digging up fresh ice from below the surface.

Several Mars rovers and landers have uncovered tantalising evidence that liquid water might flow just beneath the surface, but we still lack any conclusive evidence. However, if you broaden your timescale a bit, there is excellent evidence that in the past – perhaps a billion years or so ago – our neighbouring planet had oceans of liquid water and thicker air. In fact, conditions were pretty good to develop life as we know it even before it popped up here on Earth.

It’s entirely possible that life got a toehold (or pseudopod hold) there long ago, and died out. If that’s the case, we may yet find fossils in the Martian rocks. Again, there’s no conclusive evidence yet, but we’ve literally barely scratched the surface there. Now that it has successfully landed on Mars, we have the exciting possibility that the plutonium-powered, car-sized Curiosity rover will soon use its on-board laser and other tools to crack open and examine rocks in the Gale Crater, which were laid down billions of years ago in the presence of liquid water.

And Mars isn’t the only possibility in our solar system. Liquid water exists inside Saturn’s moon Enceladus, where geysers of liquid water erupt from deep canyons at its south pole. Energised by the gravitational tug of the giant ringed planet itself, the interior of Enceladus may be a vast ocean of liquid water even while the surface is frozen over. That doesn’t guarantee we’ll ever find alien fish swimming that moon’s seas, of course. But it’s an interesting place to look.

Europa, a moon of Jupiter, almost certainly has an undersurface ocean as well. If you relax your constraints even more, Saturn’s moon Titan has lakes of liquid methane and ethane on its surface, too. The chemistry for life would be different there – it’s a rather chilly -180C on the surface – but it’s not impossible to suppose life might arise there too.

Finding out whether this is the case means getting up close and personal. We’re doing that for Mars; however, the likes of Europa and Enceladus may have to wait a decade or four.

Phone home

But maybe we don’t have to go anywhere. Instead, we might be able to sit here and wait for alien beings (of whatever form) to message us.

Read More

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

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

Saturn broods while a storm dissipates

By Phil Plait | April 30, 2012 5:48 pm

I’m in the middle of writing up a ton of stuff for the next couple of days, so let me just leave this here: a lovely image of Saturn and its moon Tethys and Enceladus, courtesy of Cassini:

[Click to encronosenate.]

Sigh. So pretty. Tethys is the moon to the left, just above the rings, and Enceladus is right next Saturn, just below the rings. Cassini was just 1° south of the ring plane when it snapped this shot, so they appear very thin. It’s approaching northern hemisphere summer for Saturn, though, so the Sun is shining down on the rings, and they cast a wide shadow on the planet’s southern hemisphere cloud tops.

I can’t help noticing the long, thin, white ribbon of clouds about 2/3 of the way up Saturn’s northern hemisphere. That looks very much like the remnants of the gigantic storm from late 2010 that was so long it actually wrapped all the way around the planet! If you think it’s crazy to think a storm could last that long, take note that Jupiter’s Great Red Spot is at least 350 years old — it was discovered around 1665, and who knows how long it was around before then? And heck, Saturn itself suffered through a huge lightning storm for eight months.

Our gas giants don’t screw around. When they do something, they do it big.

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

Related Posts:

- Psychedelic Saturn storm!
- Saturn rages from a billion kilometers away
- Epic lightning storm electrocuting Saturn for eight months
- Crescent planet, crescent moonrise

CATEGORIZED UNDER: Astronomy, 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

A shadow falls on the ice geysers of Enceladus

By Phil Plait | April 17, 2012 6:34 am

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!

Read More

Desktop Project Part 10: The crescent and the plume

By Phil Plait | April 4, 2012 11:00 am

[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

Related Posts:

- Enceladus on full afterburner
- Life’s cauldron may be bubbling underneath Enceladus
- Enceladus!
- Enceladus does and does not have a global ocean

CATEGORIZED UNDER: Astronomy, Pretty pictures

The staring eye of a crescent moon

By Phil Plait | February 10, 2012 10:39 am

Sometimes, the images from the Cassini Saturn probe are so cool it’s tempting just to post them and say, "Look at THAT!"

See what I mean? [Click to gigantesenate.]

But of course, I can’t just leave it at that. This image, taken on January 4, 2012, is a bit different than most. Sure, we see Saturn’s magnificent rings, nearly edge on from this perspective. And we’ve seen this icy moon Enceladus many, many times (see Related Posts below for tons more pictures). Look at the bottom of the moon: see those fuzzy streaks? Those are geysers of water spewing from cracks in the moon’s south pole! Cassini has been studying them intently ever since they were discovered; they are proof that liquid water exists under the surface of Enceladus, though it’s still being argued over whether it’s in pockets, like lakes, or the whole moon has an ocean of water under the surface.

Despite all that, I keep getting drawn to the crescent shape itself. We can never see that from Earth. Saturn is much farther out from the Sun than we are, and geometry demands that from home we always see these worlds nearly fully lit by the Sun. The only way to see them like this is to go there.

But also, that giant circular feature is really interesting. It’s big, maybe 200 km (over 100 miles) across, and a bit darker than the surrounding surface. I tried locating it on an atlas of Enceladus, but it wasn’t obvious at all. I thought it might be an impact basin, but a little scrounging online led me to a paper by Cassini imaging team leader Carolyn Porco, which says there are no large impact basins on Enceladus! So what is it?

Well, why not go to Dr. Porco herself? I sent her a note, and she kindly replied. That region is called Diyar Planitia, and it stands out among the surrounding terrain because it’s much smoother. It does have narrow surface features, but they’re too small to be seen at this resolution. At the low angle at which we’re seeing it here, it looks a little bit darker than the rougher terrain around it, so it’s easier to see (which is why on an atlas it’s harder to find). It is roughly circular, but that may simply be coincidence. Enceladus has been massively resurfaced, with some areas much older than others, due to various forces under the surface — looking this all up I learned a new one, called diapirism, where lower density material underneath higher density material can rise up and break through. That’s one process that’s helped change the surface of Enceladus over the eons.

That’s pretty nifty. And think about that! Today I learned of what is to me a new region of the solar system, one that has an interesting and complicated history, molded by vast forces over long-stretched times, one of which was also new to me. How wonderful to get all that from what’s otherwise just a pretty picture!

But of course, in science, there’s no such thing as just a pretty picture. Science is a tapestry, a vast complex fabric interwoven with countless threads. Each of those threads is amazing, each important, and each leads to another. And that’s where the true beauty of science lies.

Related posts:

- Enceladus sprays anew!
- Enceladus fires on Alderaan
- Saturn weather forecast: rings, with light rain from Enceladus
- Icy moon and distant rings

The scale of Saturn

By Phil Plait | December 19, 2011 10:45 am

With the Cassini spacecraft orbiting Saturn and making frequent fly-bys of all the weird moons there, it’s easy to post one incredible close-up after another. But sometimes, you have to take a step back and get some context, see the bigger picture.

Cassini can do that, too. And when it does, the beauty and scale of the Saturn system is simply breathtaking:

[Click to encronosate.]

This image shows, of course, the ringed planet itself, with the rings seen edge-on and their shadow cast across the planet’s southern hemisphere cloud tops. But look to the left, just below the rings; see that half-lit disk? That’s Enceladus, an icy moon of Saturn. It’s about 500 km (310 miles) across, which may start to give you an idea of how much area this picture covers. Even though it’s as big as my home state of Colorado, it’s positively dwarfed by the looming presence of Saturn behind it… and we’re not even seeing very much of the planet here! Saturn is over 120,000 km (75,000 miles) across, nine times the diameter of Earth.

Saturn is big.

To pound this home, look even farther to the left of Enceladus. See that black speck? I’ve enlarged the picture and annotated it here; the arrow points to Epimetheus, a lumpy gray potato moon of Saturn. It’s about 113 km (70 miles) long. That’s small for a moon, perhaps, but on a human scale it’s a huge rock, more than ten times the height of Mt. Everest.

Yet it’s a speck in this picture, easily missed if you didn’t know it was there. But I guess that’s not surprising; Cassini was 1.2 million km from Saturn when it took this shot, three times the distance from the Earth to the Moon!

Sometimes people ask me, what’s the one thing you wish people understood better about the Universe? And if I had to pick just one only, it would be this: scale.

The Universe is huge, and we’ve barely dipped our toes into it.

Image credit: NASA/JPL-Caltech/Space Science Institute. Tip o’ the meterstick to Carolyn Porco.

Related posts:

- An icy Titanic encounter
- Enceladus fires on Alderaan
- Saturn weather forecast: rings, with light rain from Enceladus
- Enceladus sprays anew!

CATEGORIZED UNDER: Astronomy, Pretty pictures

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