Tag: Tethys

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

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CATEGORIZED UNDER: Astronomy, Pretty pictures

The immensity of Saturn

By Phil Plait | January 6, 2012 7:00 am

Carolyn Porco, the leader of the Cassini spacecraft imaging team, tweeted about this picture last night, and it’s simply overwhelming:

This is a stunning portrait of Saturn taken by the Cassini spacecraft in December. Its beauty and fantastic — in the literal sense of being like a fantasy — cloudscape are so overwhelming you might not even notice the moon Tethys hanging just under the knife-edged rings. To give you an idea of how immense Saturn is, "tiny" Tethys is over a thousand kilometers across.

This picture was taken using an infrared filter, where details in the clouds come out. That, plus the shadow of the rings on the southern hemisphere, make this one of my favorite pictures of Saturn I’ve seen in quite some time.

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

Watch out, Titan! Vader's onto you!

By Phil Plait | August 8, 2011 7:00 am

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.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

Cassini's pentaverate

By Phil Plait | June 2, 2011 9:30 am

I haven’t posted a Cassini picture in quite some time. To make up for that, here’s a stunner of a family portrait showing five worlds!

[Click to enchronosate.]

This shot shows Saturn’s rings nearly edge-on, but dominating the scene is Rhea, 1500 km (950 miles) in diameter, seen here 61,000 km (38,000 miles) distant. Below it is Dione, to the right and just above the rings is Epimetheus, and Tethys is all the way on the right, below the rings.

So what’s the fifth moon? Look to the right of Dione, right at the rings. See that tiny bump? That’s dinky Prometheus, all of 119 km (71 miles) along its longest dimension — it’s basically a spud orbiting Saturn. Prometheus, along with its sister moon Pandora, act like shepherds, keeping Saturn’s F-ring particles entrained.

Saturn is a weird, weird place, and it’s orbited by a diverse collection of weird, weird moons. I forget that sometimes, but images like this really drive it home.

… on the other hand, as we discover more planets orbiting other stars, we see lots of them with masses like Saturn’s. Of course, low-mass planets like Earth are much harder to find, but still. Who knows? It may turn out Saturn’s normal, and we’re the weird ones.

… and if you’re wondering about the post title, this may help. Whoa, man.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

Crescent planet, crescent moonrise

By Phil Plait | August 17, 2010 7:00 am

Oh. My.

Another lovely, stunning Cassini image: A thin crescent Enceladus rising over the sunlit cloud tops of Saturn:


What a sight! As the spacecraft rounded into the dark side of Saturn, it turned back toward the planet (and the far more distant Sun). The top of Saturn’s atmosphere is still lit as seen from Cassini’s vantage point, but also lit was the moon Enceladus. The moon was between Saturn and Cassini, and so the geometry dictates it too was showing almost entirely its dark side to the spacecraft. The result is the thin crescent of the moon just over the (only partially seen) thinly lit crescent of its parent planet.
Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures

Megameter chasm on an icy moon

By Phil Plait | July 29, 2010 1:52 pm

I know I haven’t been posting much astronomy the past few days — Comic Con, w00tstock, and "Bad Universe" have kept me hopping — so to make up for it a little bit, here’s a lovely image sent back a billion kilometers from Cassini:


This is Tethys, an ice moon of Saturn. The angle of Cassini, Tethys, and the Sun light the moon as a crescent. The most obvious feature is Ithaca Chasma, a (more than) thousand-kilometer-long gash in the side of the object. Note that Tethys is only about 1000 km in diameter, so the chasm runs along a third of the moon’s surface (circumference = diameter x π, remember).

How big is that? Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: Cassini, Tethys

A billion km distant ice mountain against the black

By Phil Plait | July 14, 2010 3:03 pm

Carolyn Porco just tweeted about a beautiful image from Cassini, showing the icy moon Tethys hanging in space:


How forbidding and lovely!

Tethys is big, about 1100 km (660 miles) across (about 1/3 the diameter as our own Moon). Its density is actually a bit less than that of water, so it’s most likely predominantly composed of water ice. The surface is bombarded with craters, including the big one at the bottom called Melanthius. Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: Cassini, Melanthius, Tethys

An otherworldly eclipse

By Phil Plait | January 25, 2010 12:00 pm

What’s this? Two outstanding and surpassingly beautiful Cassini images in one day?

Yeah, because this is how much I love you guys. Check. This. Out:


[Click to embiggen.]

That is so cool! It’s Saturn’s moon Dione passing in front of Tethys as their mutual motion, combined with Cassini’s, give us this incredible view of what astronomers call an occultation (also called a "mutual event"… but you can just think of it as an eclipse).

There’s so much awesomeness in this picture. For one, see the faint glow on the "dark" side of Tethys? That’s reflected light from Saturn, which is well off to the right in this picture. But we don’t see any reflected light on Dione. Why not?

Even though the two moons look about the same distance away, that’s very misleading: in this image, Tethys is 2.6 million kilometers (1.6 million miles) from Cassini, while Dione is 400,000 km (240,000 miles) closer. That’s enough to significantly change the geometry of the situation, so that we don’t see Saturnlight on Dione.

Note that while both moons are roughly the same size (Tethys is 1062 km (660 miles) across, and Dione is 1123 km (700 miles) in diameter), Dione looks bigger because it was closer to Cassini when these shots were snapped. If they had been at the same distance from Cassini, you’d just barely be able to tell Dione is bigger. Sometimes distance matters, not size.

And sometimes size matters too. It’s hard to miss the vast Odysseus crater on Tethys, a terrifying 400 km (240 miles) across. That’s the size of Ohio. An impact that large on Earth would pretty much wipe out every living thing on the planet’s surface.

For another little dose of coolness, these images were taken about one minute apart, covering just two minutes of Cassini’s tour of Saturn and its armada of moons. Imagine what you’d see if you could be there, staying at a hotel orbiting Titan? What wonders would befall your eyes if you had years to explore?

Hmmm. Come to think of it, we don’t have to wonder about it. Cassini is showing us.

Credit: NASA/JPL/Space Science Institute

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: Cassini, Dione, Tethys

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