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Cassini Finds Saturn's Rings Are Weirdly Thin

If a material is thicker, it should be less transparent, right? It turns out that in Saturn's rings, that's not always the case.

If a material is thicker, it should be less transparent, right? It turns out that in Saturn's rings, that's not always the case. A new examination of the B ring shows that even though it's the most opaque of Saturn's rings, it's not the densest one.

ANALYSIS: Mysterious ‘Spokes' in Saturn's Rings are Still There

The puzzling result is not just isolated to this ring, either. Scientists have found similar results in other studies when looking at the gas giant's other rings, NASA said. This latest research comes from using the Cassini spacecraft, which is slowly wrapping up investigations at Saturn since arriving there in 2004.

"Appearances can be deceiving," said research co-author and Cassini co-investigator Phil Nicholson, at Cornell University in New York, in a NASA statement. "A good analogy is how a foggy meadow is much more opaque than a swimming pool, even though the pool is denser and contains a lot more water."

The research team looked at the ring's mass density by studying spiral density waves. These features appear when ring particles move under the influence of gravity - gravity from Saturn's moons as well as the huge gas giant planet itself. Each wave's structure depends on how dense it is, and the effect of gravity. Scientists now know that the B ring is less dense than it appears, but the full reason is still a mystery.

NEWS: Propellers Reveal Hidden Moons in Saturn's Rings

"It could be something associated with the size or density of individual particles, or it could have something to do with the structure of the rings," stated Matthew Hedman, the study's lead author and a Cassini participating scientist at the University of Idaho.

While Saturn's rings are arguably the most spectacular in the solar system, it's not the only planet with rings. Jupiter, Uranus and Neptune also have faint ring systems of their own. Maybe this implies different origin stories, but more study will be needed to figure this out for sure. NASA says Saturn's rings - made up of billions of particles and pieces - are likely fragments of broken-up moons, comets or asteroids that were pulled apart under Saturn's gravity.

The major features in Saturn's rings are labelled in this image, which is cropped from a panoramic view of the planet. | NASA/JPL-Caltech/Space Science Institute

ANALYSIS: Cassini Grand Finale: Saturn Mission's Daring End

Saturn's B ring was studied before using Cassini's composite infrared spectrometer, but this study took a bit of a different approach. Using visible and infrared light, the team looked at a bright star in between the rings. They also combined the results of multiple observations, making it possible to see even more subtle ring waves than before.

By looking at how dense the rings are, this could help scientists pin down the age of Saturn's rings, which are considered relatively young compared with the more than 4.5 billion years the solar system has been around.

"A less massive ring would evolve faster than a ring containing more material, becoming darkened by dust from meteorites and other cosmic sources more quickly," NASA wrote in the same statement. "Thus, the less massive the B ring is, the younger it might be - perhaps a few hundred million years instead of a few billion."

PHOTOS: Why Are Craters on Saturn's Moons Vanishing?

The study was published in the journal Icarus. The Cassini mission will complete its work next year when, low on fuel, the spacecraft will deliberately crash into Saturn to avoid contaminating icy moons in the region that could be hospitable to life, such as Enceladus.

The Cassini mission is investigating Saturn in detail, including the structure of its rings.

Something is erasing craters on several moons of Saturn. And here's the neat thing -- it's likely a different process for each moon studied, according to the authors who developed a model for it. The results are published

in a new Icarus paper

called "Surface ages of mid-size Saturnian satellites" led by Romina Di Sisto (part of the faculty of astronomy and geophysics at Universidad Nacional in Argentina). The authors compared their theoretical predictions with "crater counts" (from other scientists) of Cassini and Voyager images of several Saturn satellites and concluded there are fewer smaller craters than predicted. Here are some of the most likely crater-erasing processes on several moons of Saturn. The authors plan to continue their work with Titan and other Saturnian moons in the future.

There are geysers regularly erupting from Enceladus,

particularly from four parallel fractures

("tiger stripes") near the south pole, according to a 2006 study. Craters would be erased both by the plumes and some tectonic activity.

Some of the material escapes Enceladus

and populates Saturn's E ring, while the rest falls back on to the surface and erases craters, according to a 2010 study.

While Iapetus has an old surface, astrophysicists have noticed that the leading side of the moon is dark, while the trailing side is brighter. While it's unclear what is causing this difference, some theories include internal processes or perhaps debris or dust material falling from other moons of Saturn, to the darker side of Iapetus. In 2010, a study

suggested that both processes

may be at work at once if the dark material is falling on the leading hemisphere, triggering a runaway global dispersement of water ice.

A team of researchers

looked for plumes on Mimas

and said in 2011 that their search was in vain, according to Di Sisto. Therefore, there must be some sort of lower-level geologic activity that is reshaping the surface. Since Mimas is among the moons that could have an icy subsurface ocean, perhaps there is something related to that in the interior causing the crater erasure on the outside, Di Sisto's team suggests.

In the same study that looked at Mimas in 2011, the scientists of that study also

concluded that Tethys has no plumes

. When looking at Tethys in far ultraviolet light, a weird picture emerges; its leading hemisphere is brighter than the trailing hemisphere, according to Di Sisto. Also, its surface appears strangely porous. Perhaps it is being pummeled with material from Saturn's E ring. Or, there could be geologic activity that hasn't yet been detected by Cassini.

Dione also appears bereft of plumes

, at least when looking for vapor production that is too orders of magnitude smaller than what has been observed on Enceladus. "However, plume activity cannot be absolutely ruled out because it can be under the detection limit," Di Sisto wrote. Like Tethys, Dione is also brighter on its leading hemisphere than its trailing one. While Di Sisto did not suggest what process could be causing the craters to erase, Di Sisto did point out that Dione has a tenuous atmosphere (

as per a separate 2011 study

.)

A couple of neat things about Rhea -- a 2010 study found it has a

tenuous atmosphere of oxygen and carbon dioxide

that may be created by surface water ice decomposing due to radiation from plasma (ionized gas) from Saturn's magnetosphere. Also, that

plasma appears to affect the surface

, a 2012 study concludes. This could account for why small craters are erased on the surface of Rhea, Di Sisto suggests.