Scientists solve planetary ring riddle

In a breakthrough study (‘Size distribution of particles in Saturn’s rings from aggregation and fragmentation’), published in the academic journal Proceedings of the National Academy of Sciences (PNAS), an international team of scientists has solved an age-old scientific riddle by discovering that planetary rings, such as those orbiting Saturn, have a universally similar particle distribution.

Mimas by Saturnshine

Although we are used to seeing Saturn’s moons lit directly by the Sun, sometimes we can catch them illuminated by “Saturnshine.” Here, we see Mimas (upper right) lit by light reflected off of Saturn. 

NASA/JPL-Caltech/Space Science Institute

Serene Saturn

From a distance Saturn seems to exude an aura of serenity and peace. 

NASA/JPL-Caltech/Space Science Institute

Saturn and its rings at the end of '600

The picture shows a pastel drawing created between 1693 and 1698 by Maria Clara Eimmart, German astronomer and illustrator, who died in 1707 at the age of 31. The drawing is based on an engraving by the famous Dutch astronomer Christiaan Huygens, who was the first to realize that the strange growths on either side of Saturn formed a ring separated from the body of the planet. Eimmart’s drawing wasn’t simply reporting what Huygens saw, but also collected the observations of more than ten astronomers, thus providing a notable document on how Saturn was seen at the end of '600, the first century in which humans scrutinized the sky not only with the naked eye, but with the aid of rudimentary, yet effective, telescopes.

Saturn’s faint D ring

Not all of Saturn’s rings are created equal: here the C and D rings appear side-by-side, but the C ring, which occupies the bottom half of this image, clearly outshines its neighbor. 

NASA/JPL-Caltech/Space Science Institute

Titan flybys: How gravity assists work

For the past 18 months, NASA’s Cassini spacecraft has been orbiting Saturn in practically the same plane as the one that slices through the planet’s equator. Beginning with the Titan flyby on May 22, navigators started to tilt Cassini’s orbit in order to obtain a different view of the Saturnian system. The measure of the spacecraft orbit’s tilt relative to Saturn’s equator is referred to as its inclination. The recent Titan flyby raised Cassini’s inclination to nearly 16 degrees. Seven more Titan flybys will ultimately raise Cassini’s inclination to nearly 62 degrees by April 2013. On Earth, an orbit with a 62-degree inclination would pass as far north as Alaska and, at its southernmost point, skirt the latitude containing the tip of the Antarctic Peninsula.

It's been nearly two years since NASA's Cassini spacecraft has had views like these of Saturn's rings. These views are possible again because Cassini has changed the angle at which it orbits Saturn and regularly passes above and below Saturn's equatorial plane. Steeply inclined orbits around the Saturn system also allow scientists to get better views of the poles and atmosphere of Saturn and its moons. A group of scientists has restarted the team's studies of propeller-shaped gaps. These gaps are cleared out by objects that are smaller than known moons but larger than typical ring particles. Cassini scientists haven't seen propellers in two years. Because some of the propellers are exactly where models predicted they would be, scientists believe they are seeing some old friends again. Credit: NASA/JPL-Caltech/SSI/Cornell

Tropical lakes on Titan

The existence of oceans or lakes of liquid methane on Saturn's moon Titan was predicted more than 20 years ago. But with a dense haze preventing a closer look it has not been possible to confirm their presence. Until the Cassini flyby of July 22, 2006, that is. Radar imaging data from the flyby, published in the journal Nature, provide convincing evidence for large bodies of liquid. Intensity in this colorized image is proportional to how much radar brightness is returned, or more specifically, the logarithm of the radar backscatter cross-section. The colors are not a representation of what the human eye would see. The lakes, darker than the surrounding terrain, are emphasized here by tinting regions of low backscatter in blue. Radar-brighter regions are shown in tan. Smallest details in this image are about 500 meters (1,640 feet) across. Credit: NASA/JPL-Caltech/USGS

Methone and Tethys

NASA's Cassini spacecraft captured these raw, unprocessed images of Saturn's moons Methone and Tethys on May 20, 2012. With a close-approach distance of about 1,200 miles (1,900 kilometers), this was Cassini's closest flyby of the 2-mile-wide (3-kilometer-wide) Methone.

This raw, unprocessed image of Methone was taken on May 20, 2012 and received on Earth May 21, 2012. The image has not been validated or calibrated. Credit: NASA/JPL-Caltech/SSI