Nine moons, 62 Hours for (long) weekend warrior

Oct 20, 2010 By Jia-Rui C. Cook
These three views of Saturn's moon Rhea were made from data obtained by NASA's Cassini spacecraft. Image credit: NASA/JPL/SSI/LPI

Taking a long-weekend road trip, NASA's Cassini spacecraft successfully glided near nine Saturnian moons, sending back a stream of raw images as mementos of its adrenaline-fueled expedition. The spacecraft sent back particularly intriguing images of the moons Dione and Rhea.

The Dione and Rhea pictures are the highest-resolution views yet of parts of their surfaces. The views of the southern part of Dione's leading hemisphere (the part of the moon that faces forward in its orbit around ) and the equatorial region of Rhea's leading hemisphere are more detailed than the last time we saw these terrains with NASA's in the early 1980s.

Of the five big icy moons of Saturn, Dione and Rhea are often considered a pair because they orbit close to each other, are darker than the others, and exhibit similar patterns of light reflecting off them. These new images, however, highlight the differences between these sister moons.

Both images show similar geographic regions on each satellite. However, scientists can identify differences in geological histories of the two bodies from differences in the numbers and sizes of visible craters on their surfaces. The number and size of craters on a body's surface help indicate the age of that surface – the more craters there are and the larger they are, the older the surface is.

Rhea, for example, shows ancient, intense bombardments throughout this region. However, the same region of Dione is divided into distinct areas that exhibit variations in the number and size of preserved craters. In particular, while parts of Dione are heavily cratered like Rhea, there are other areas covered by relatively smooth plains. Those areas have many small craters, but few large impact scars, which indicates that they are geologically younger than the heavily cratered areas. The smooth plains must have been resurfaced at some point in Dione's past -- an event that seems to be missing from Rhea's geological history on this side of the moon.

NASA's Cassini spacecraft captured a picture of the tiny, 4-kilometer-wide (3-mile-wide) moon Pallene, in front of the planet Saturn. Image credit: NASA/JPL/SSI

Images of the moon Mimas, captured just before it went into shadow behind Saturn, will be compared to thermal maps made earlier this year that showed an unexpected "Pac-Man" heat pattern. (See for more details.)

Cassini also caught a picture of the tiny, 4-kilometer-wide (3-mile-wide) moon Pallene, in front of the planet Saturn, which is more than 120,000 kilometers (75,000 miles) wide at its equator.

Cassini's elliptical orbital pattern around Saturn means it can target moons for flybys about once or twice a month. The flybys on this particular Cassini road trip were "non-targeted" flybys, meaning navigators did not refine Cassini's path to fly over particular points on each moon.

Cassini's long weekend started on Thursday, Oct. 14, at 5:07 p.m. UTC (9:07 a.m. PDT), when it passed by Saturn's largest moon Titan at an altitude of 172,368 kilometers (107,104 miles) above the surface. Then came a whirlwind 21 hours in which Cassini flew by Polydeuces at 116,526 kilometers (72,406 miles), Mimas at 69,950 kilometers (43,465 miles), Pallene at 36,118 kilometers (22,443 miles), Telesto at 48,455 kilometers (30,109 miles), Methone at 105,868 kilometers (65,783 miles), Aegaeon at 96,754 kilometers (60,120 miles) and Dione at 31,710 kilometers (19,704 miles). Cassini's last visit -- Rhea at 38,752 kilometers (24,079 miles) – took place at 6:47 a.m. UTC on Oct. 17 (10:47 p.m. PDT on Oct. 16).

Scientists decided in advance which observations they wanted to make while the spacecraft was cruising past all the moons. They chose to obtain images of Titan, Mimas, Pallene, Dione and Rhea. They also obtained thermal scans of Mimas, and Rhea.

Explore further: Bad weather delays SpaceX launch with 3-D printer

Related Stories

Cassini's Photo Album From a Season of Icy Moons

Dec 07, 2005

Wrapping up a phenomenally successful year of observing Saturn's icy moons, the Cassini mission is releasing a flood of new views of the moons Enceladus, Dione, Rhea, Hyperion and Iapetus.

Rhea's Wisps in Color

Feb 28, 2006

Bright, wispy markings stretch across a region of darker terrain on Saturn's moon Rhea. In this extreme false-color view, the roughly north-south fractures occur within strips of material (which appear greenish ...

Cassini Finishes Saturnian Doubleheader

Apr 12, 2010

(PhysOrg.com) -- NASA's Cassini spacecraft completed its double flyby this week, swinging by Saturn's moons Titan and Dione with no maneuver in between. The spacecraft has beamed back stunning raw images of ...

Space Image: Ghostly Encounter

Jun 29, 2010

(PhysOrg.com) -- The surface of Saturn's moon Dione is rendered in crisp detail against a hazy, ghostly Titan. Visible in this image are hints of atmospheric banding around Titan's north pole.

Cassini flies by Saturn's tortured moon Mimas

Aug 05, 2005

On its recent close flyby of Mimas (MY-muss), the Cassini spacecraft found the Saturnian moon looking battered and bruised, with a surface that may be the most heavily cratered in the Saturn system.

Cassini Doubleheader: Flying By Titan and Dione

Apr 05, 2010

(PhysOrg.com) -- In a special double flyby early next week, NASA's Cassini spacecraft will visit Saturn's moons Titan and Dione within a period of about a day and a half, with no maneuvers in between. A fortuitous ...

Recommended for you

Internet moguls Musk, Bezos shake up US space race

Sep 20, 2014

The space race to end America's reliance on Russia escalated this week with a multibillion dollar NASA award for SpaceX's Elon Musk and an unexpected joint venture for Blue Origin's Jeff Bezos.

Winter in the southern uplands of Mars

Sep 19, 2014

Over billions of years, the southern uplands of Mars have been pockmarked by numerous impact features, which are often so closely packed that they overlap. One such feature is Hooke crater, shown in this ...

Five facts about NASA's ISS-RapidScat

Sep 19, 2014

NASA's ISS-RapidScat mission will observe ocean wind speed and direction over most of the globe, bringing a new eye on tropical storms, hurricanes and typhoons. Here are five fast facts about the mission.

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

deatopmg
1 / 5 (1) Oct 20, 2010
Will we, the paying public, ever get to see these "raw" images or just the highly compressed jpeg's?
yyz
not rated yet Oct 21, 2010
"Will we, the paying public, ever get to see these "raw" images or just the highly compressed jpeg's?"

I'm curious, why do you seek access to full size uncompressed 'raw' images from the Cassini mission? Do you think NASA is hiding something from us? You know, you can find just as much evidence for alien civilizations photoshopping lossy jpegs as from the 'raw' originals.