Iapetus travels in a tidally locked orbit with Saturn, always showing the same face to the planet. When Cassini Regio, the moon's dark hemisphere, faces the Earth, however, it nearly disappears from view, coated entirely in a mysterious black substance that is gradually creeping across the sphere. Astronomers have long speculated on the nature of the substance, which gives the moon an unusually uniform surface, and while many believe that it is composed of the dirt left behind when ice on Iapetus sublimates, they hope that new data from the Cassini spacecraft will offer more concrete clues, as well as help them understand the nature of the equatorial ridge that travels across Cassini Regio, an odd phenomenon in a surface otherwise marked by impact craters.

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Daphnis, which is just eight kilometers in diameter, is one of Saturn's shepherd moons, tracing its orbit inside the Keeler gap in Saturn's main ring. It appears as a pin prick of light, but its gravity is sufficient to pull the ring's edges out of their plane, forming undulating vertical structures. Although astronomers have predicted the waves through simulations, they have never before been captured on film. But as Saturn approaches it equinox — an event that occurs once every 15 Earth years — the rings are illuminated in such a way that shadows from the waves are visible on the A Ring, allowing Cassini to photograph the phenomenon for the first time.

Images from Cassini Equinox Mission and CICLOPS via International Space Fellowship.

It reminds me of the pop art masterpiece NASA created with UV solar images a while back. [Riding With Robots]

Most auroras in the solar system, including Earth's, are caused by the interaction between charged particles in the solar wind and a planet's magnetic field. Saturn has a main aurora that is caused by the solar wind. Jupiter has an aurora caused by the interaction of Jupiter's magnetic field and the magnetic properties of its moons. The infrared aurora on Saturn doesn't fit either of those models. University College London astronomer Nick Achilleos, a member of the Cassini team, said, "Trying to explain its origin will no doubt lead us to physics which uniquely operates in the environment of Saturn."

Scientists will keep an eye on the phenomena in an effort to find more clues about its nature. So far, the aurora has been observed to be highly variable, shifting in size and even periodically disappearing. Image by: NASA/JPL/University of Arizona.

Cassini Finds Mysterious New Aurora On Saturn. [Science Daily]

1. Titan is the only moon with a thick, stable atmosphere. It's mostly made of nitrogen, with a decent helping of methane and other hydrocarbons. It's not exactly a breathable atmosphere, but it's still pretty cool. Even better, Titan has Earth-like weather. Wind and rain sweep the surface of Titan, shaping its geography and producing seasonal effects. Some scientists say Titan is a lot like a young Earth, only much colder.

2. Titan has dune seas. As much as 40 percent of the equatorial region might be covered by "sand" dunes hundreds of meters high. They probably aren't made of silicate particles the way Earth sand is. Rather, Titan's sand could be precipitated from the atmosphere. The dunes are sort of like semi-permanent snow drifts.

3. Titan has cryovolcanoes. There are mountains on Titan, along with evidence of volcanic activity. The interior of Titan probably doesn't support the same kind of heat and pressure that we find within the Earth. Instead, Titan's volcanoes might be the result of highly pressurized ice fracturing and spewing liquid water and ammonia into the atmosphere.

4. Titan has liquid features on the surface, like the hydrocarbon lakes pictured in the computer rendering above. Earlier Cassini data found proof of methane lakes in Titan's polar regions. Even more interesting, there might be an entire ocean lying beneath Titan's surface. This leads us to the best reason that Titan is awesome...

5. Titan might be our best bet for finding extraterrestrial life within our solar system. If the subsurface ocean exists, it would be made of liquid water and ammonia and would be warmer than the surface. The chemical makeup of the atmosphere and the active weather and geology have lead some scientists to propose that the conditions on Titan are right for the formation of primitive life. That's exciting. Image by Steven Hobbs via NASA.

Scientists began to suspect a global ocean when they saw some landmarks on Titan had shifted up to 19 miles between October 2004 and May 2007. The best explanation is a vast ocean, separating the planet's icy crust from its rocky center. The Cassini Space probe will fly within 620 miles of Titan, sample the atmosphere, and take pictures of the site where the Huygens probe landed.

At least we can console ourselves with this artist's rendering of what it would look like to be zooming through Enceladus' plumes if they were visible to the naked eye.

Cassini probe failed to 'taste' moon's geysers in flyby [New Scientist]

Images by NASA/JPL. [Science Daily]

The water has none of the sodium which it would have after years of contact with rock, claims University of Colorado scientist Nick Schneider. But other scientists argue there might be sodium which Schneider's telescope analysis failed to detect. And even Schneider isn't claiming there's no ocean on Enceladus, just that the water jets don't come from it. NASA may have to mount a mission to find out for sure if the Saturn moon holds life forms. Image by NASA/JPL [BBC]