Category: Saturn

Saturn’s moon Iapetus is one of the most mysterious objects in the Solar System. It’s shaped like a football, has a strange ridge that runs along most of its equator, and it’s got vastly different hemispheres. One side is as white as driven snow, and the other side is dark as tar. Scientists think they’ve at least got an answer for this last mystery.

Even before humans sent spacecraft to Saturn, astronomers have known there’s something bizarre about Iapetus. Its brightness changed significantly depending on its facing towards the Earth. Follow up observations with spacecraft, like Voyager and Cassini showed that this was because half the moon is covered in snowy white material, while the other half is dark as night.

During its most recent flyby, NASA’s Cassini spacecraft confirmed that Iapetus is warm enough on the dark side – 127 Kelvin (-230 F) – that water vapour can slowly release from water ice. This vapour then travels around the moon, and freezes back down onto the white side. This process of vaporization and accumulation is called “thermal segregation”.

So where does the dark material come from? Astronomers think that it didn’t originate on Iapetus, but instead came from the surrounding outer moons. As Iapetus goes around its orbit, this darker material piles up on the leading hemisphere. The material heats up the surface of moon, allowing it to release the water vapour which then reforms on the other side.

Scientists describe this as a runaway process. Once it got going, both hemispheres went to extremes. The water completely boiled away from the dark side, and then accumulated on the bright side. You don’t see shades of grey, just black and white.

Thanks to Cassini’s recent flyby, planetary geologists think they’re getting a handle on the moon’s strange football shape and the equatorial ridge too, but those will come with future research papers.

Original Source: NASA/JPL/SSI News Release

We asked, and Cassini delivered; amazing, intriguing images of the surface of Saturn’s moon Iapetus. The spacecraft completed its latest flyby on September 10th, 2007, skimming just 1,640 km above the moon’s surface. Scientists will be digesting the photographs for years.

During this most recently flyby, Cassini passed 100 times closer than its previous Iapetus flyby in 2004. At this distance, the spacecraft was able to reveal the moon’s strange bulging shape, equatorial ridge, and pattern of bright and darkness across its features.

Many of its photographs focus in on the bizarre mountain ridge that circles the moon’s equator, like a seam. The new Cassini images showed that this ridge is mountainous, rising as high as 20 km, and extends across more than half its circumference.

The mystery deepens with the unusual light and dark hemispheres of Iapetus. One side is as white as snow, and the other is as black as tar. With the new Cassini images, you can actually see where the different regions mix. On the dark side, you can see spots where there are patches of white ice on dark mountainsides. And then on the bright side, you can see blobs of dark material. This dark material forms a very thin coating; probably only a few metres deep, since there are regions where impact craters have punched right through it, revealing white material underneath.

What caused this material? That’s a mystery. Maybe some previous Saturnian moon broke up, and spray painted Iapetus. Or maybe the material is volcanic material that welled up from within the moon. And this could somehow be connected with the moon’s equatorial ridge.

The images from Cassini were actually delayed early Tuesday, because a cosmic ray hit the spacecraft, putting it into safe mode. This happened after it had captured all its images from its flyby, and they were safely stored in memory. After a few hours Cassini came out of safe mode and continued sending its data back to Earth.

Original Source: ESA News Release

As I mentioned a few days ago, I’m incredibly excited about Cassini’s recently flyby of Saturn’s moon Iapetus. Passing only 1,200 km (800 miles) above the surface of the bizarre moon, the spacecraft has captured dozens of new images. Perhaps now planetary geologists can figure out what’s caused that amazing ridge, the walnut shape, and the bizarre light and dark hemispheres.

The moment the new Cassini images came in, Emily Lakdawalla from the Planetary Society jumped on them, and started analyzing. She was able to stitch together several images into a large mosaic that just looks amazing. Especially that ridge. What is up with that ridge?

There are some original raw images available from the flyby from NASA, but I highly recommend you check out Emily’s analysis while we wait for NASA’s official results.

NASA’s Cassini spacecraft is going to make one of its most important flybys of its entire mission this week, zipping past Saturn’s moon Iapetus on September 10th, 2007. I’m calling it “most important”, not NASA, but trust me, this is a big one. I’ve got two reasons for this: it’s the first time Cassini will get this close to Iapetus, and this moon is one of the strangest objects in the Solar System, with a whole collection of bizarre features.

First let’s talk about Iapetus. This is one bizarre moon. Take a look at the picture and you’ll see that it’s got what looks like a seam running across its equator. That’s not a seam, but a bizarre mountain range that runs across its equator. This ridge is 20 km (12 mile) wide and 13 km (8 mile) high, extending 1,300 km (800 miles) directly along the moon’s equator.

It’s possible that this ridge was created when the moon was spinning much more quickly than it does today. Or maybe this is some kind of icy material that welled up from within the moon and then solidified on the surface. Or perhaps the moon consumed one of Saturn’s rings, piling the material up on its surface along the equator. Whatever the case, it’s one of the strangest features in the Solar System.

Second, Iapetus has two completely different coloured hemispheres: one bright as snow and the other dark. The dark material might have come from another of Saturn’s moons, or maybe it’s organic material that rained down in the past. Perhaps it’s material that came out from the middle and hardened. But what is it? You see, this place is mysterious.

Third, it’s shaped like a walnut. You can see the strange shape just in the picture. That’s not a trick of the camera, the moon really is squashed like that. Like someone tore it in half, and then smashed it back together again. What caused it? How did it stay that way, and not turn back into a sphere?

NASA’s Voyager 2 flew past Iapetus on August 22, 1981 at a range of 966,000 km (600,000 miles) and turned up the strange shape and dark/light hemispheres. On December 31st, 2004, Cassini made its first close approach getting within 123,000 km (77,000 miles), and taking the picture I’ve attached with this story.

Well, on September 10th, 2007, Cassini will fly only 1,200 km (800 miles) above Iapetus and take its highest resolution pictures ever. Finally, I’ll get my answers. And probably a few new questions too.

I can’t wait.

Original Source: NASA/JPL/SSI News Release

Saturn’s moon Iapetus is one of the stranger objects in our Solar System. Unlike other objects its size, Iapetus is walnut-shaped, with a clearly defined chain of mountains along its equator. How could it have formed billions of years ago with the rest of the Solar System, and yet still have its unique shape?

New NASA supported researchers have developed a computer model that seems to accurately explain the series of events that Iapetus went through to arrive at its current shape.

Billions of years ago, shortly after its formation, Iapetus spun quickly, taking just 5 hours to complete a rotation. This fast spin gave it the oblate walnut shape it has today. Over time, its rotation slowed down to about 16 hours. It also cooled down enough that its surface froze solid. It couldn’t absorb the excess surface material. Instead, this rubble built up the chain of mountains around its equator. At this point, its formation completely halted in its tracks. The moon now orbits at a relatively slow rate, turning only once every 80 days.

Scientists were able to confirm these predictions for Iapetus, using observations of its rocks containing short-lived isotopes aluminum-26 and iron-60. These decay at a rate that allowed scientists to carbon date the moon at roughly 4.564 billion years old. About the same age as the Earth.

NASA’s Cassini spacecraft is due to make another flyby of Iapetus on September 10, 2007, passing within only 1,000 km (621 miles) of its surface.

Original Source: NASA Jet Propulsion

One of the most bizarre objects in the Solar System has got to be Saturn’s moon Hyperion. From the pictures taken by Cassini, this tiny moon looks like a sponge you might buy at the Body Shop. In a new research paper appearing in the July 5 issue of the journal Nature, scientists have mapped the surface of Hyperion, and found hydrocarbons, some of the building blocks of life. And they also think they know why it has such a bizarre look.

The information was gathered by Cassini’s ultraviolet imaging spectrograph and visual and infrared mapping spectrometer. These two instruments are able to map mineral and chemical constituents of a surface. In this case, the surface of Hyperion. It found that most of the surface is a mix of frozen water and organic dust, as well as trace amounts of frozen carbon dioxide.

But the key discovery are these hydrocarbons; combinations of carbon and hydrogen atoms. When these molecules are embedded in ice and then exposed to ultraviolet radiation, new complex molecules can form that are present in life.

In addition to the surface analysis, Cassini also helped scientists work out why the moon has such a bizarre spongy appearance. It all comes down to an extremely low density. According to new calculations, the moon has only half the density of water. Its low gravity means that normal processes, such as crater formation work differently than on more dense objects in the Solar System. Objects that impact Hyperion plunge in, compressing the surface instead of blasting out the familiar looking craters.

Original Source: NASA