Tag: Pandora

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

Cassini gives Dione a close shave

By Phil Plait | December 13, 2011 6:00 am

The Cassini spacecraft has been touring Saturn and its moons for 7 years now, and yet still manages to send back images that are simply astonishing. Just yesterday, the probe swung past the icy moon Dione at a distance of just 99 kilometers (62 miles) over the surface! Compare that to the moon’s diameter of over 1100 km (670 miles) and you get an impression of how close that was.

The purpose of the pass was to get infrared spectra of the moon, so only a few visible light images were taken. But oh, what pictures they were! Check this out:

Wow! Dione dominates the view, its cratered surface of ice looking like a golf ball that had a dimpling machine accident. You can see Saturn’s rings on the left, nearly edge-on, and two more moons as well: the gray lumpy potato of Epimetheus, only about 130 km (70 miles) across, and Prometheus, also about 136 km along its long axis. My first guess is that Prometheus is farther away than Epimetheus in this shot, since it looks smaller (I wondered for a second if it’s possible we’re seeing it rotated a bit so it’s pole-on, but it’s a very elongated rock; so we’re definitely seeing it mostly from the side here).

After seeing that picture, I excitedly grabbed the next one, and got confused for a moment:

Now, wait a sec. There’s Dione, the rings, and Epimetheus. See how before, Epimetheus was mostly above the rings, but now it’s mostly lower? That means Cassini moved up a little bit from the plane of the rings, so the little moon looks like it moved down. So then why did Prometheus move up?

Because it didn’t. That’s not Prometheus, it’s Pandora! A different moon, though they’re related: they are shepherd moons, which means they have very similar orbits, and occasionally swap places! It’s weird, but I’ve explained it before. Anyway, Pandora and Prometheus are almost exactly the same size, and both are elongated like an Idaho spud. So I’m not too surprised I was confused for a moment when I saw the second picture. When you look a little more closely you can see the shapes are different, though.

More pictures were returned from the pass (including a couple showing Mimas peeking out from behind Dione), so you should take a look. They’re pretty dramatic.

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


Related posts:

- The real Pandora, and two mooning brothers
- Dr. Tongue’s 3D House of Prometheus
- Cassini eavesdrops on orbit-swapping moons
- The bringer of fire, hiding in the rings

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

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?

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


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 trillion and five moons

By Phil Plait | September 13, 2011 9:45 am

On July 29, 2011, the unending dance of Saturn’s moons lined them up perfectly for a stunning view by the Cassini spacecraft: five moons arrayed for your pleasure:

[Click to embiggen.]

From left to right that’s Janus, Pandora (in the rings), Enceladus, Mimas, and Rhea. Perspective plays a role here; Rhea is three times bigger than Enceladus, but was much closer to Cassini when this picture was taken, so it looks even bigger.

But the moons themselves are so different from each other! Janus is a lump, too small to have enough gravity to crush itself into a sphere. Enceladus is mostly ice, so it appears very bright in this image compared to its rocky siblings. You can just barely see part of the monster crater Herschel peeking out of the dark side of Mimas, while Rhea is peppered with smaller craters. And Pandora orbits inside Saturn’s rings themselves, its meager gravity enough to entrain the particles in the thin F ring and keep it in place.

And, of course, the rings themselves, composed of countless tiny ice crystals. Over millions of years, collisions have ground them into pieces ranging in size from barely big enough to see to perhaps 10 meters across, the volume of a roomy two-car garage.

Amazing. And this vista was taken just a couple of weeks after Cassini’s seventh anniversary in orbit around Saturn. Even after all that time, and tens of thousands of images, it still has the capability to take our breath away.


Related posts:

- Cassini’s Pentaverate
- Cassini’s slant on the rings
- A little weekend Saturn awesomeoness
- The real Pandora, and two mooning brothers

CATEGORIZED UNDER: Astronomy, Pretty pictures

The real Pandora, and two mooning brothers

By Phil Plait | May 6, 2010 11:45 am

Cassini continues making loop-de-loops around Saturn, returning tens of thousands of way cool pictures. Like this one:

cassini_epimetheus_pandora

From 1.3 million kilometers (800,000 miles) away — 3 times as far as the Moon is from the Earth — Cassini spied this pretty scene. It shows, obviously, Saturn’s rings to the right. The very thin ring extending to the left is the F-ring; it’s very faint and wasn’t even discovered until 1979, when Pioneer 11 passed the planet.

The two moons are Pandora (the flying saucer-shaped one) on the left, and Epimetheus on the right. Usually, in pictures like this, perspective is a problem; one moon is much farther away than the other, so your sense of scale gets a bit bollixed. But in this case, both moons are about the same distance from Cassini! Pandora is about 114 x 84 x 63 km (68 x 50 x 38 miles) in size, and Epimetheus is a bit heftier at about 144 x 108 x 98 km (86 x 64 x 58 miles). In this shot, the rings are in the background relative to the moons, and Pandora is just a hair closer to Cassini than Epimetheus.
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CATEGORIZED UNDER: Astronomy, Pretty pictures
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