Image: Rhea and Titan
NASA / JPL-Caltech / SSI
Craters appear well-defined on icy Rhea in front of the hazy orb of larger Titan in this view of the two Saturn moons. NASA's Cassini spacecraft snapped the photo on Dec. 10, 2011.
updated 2/19/2012 10:48:15 PM ET 2012-02-20T03:48:15

Saturn's two biggest moons hang together in a stunning new photo from NASA's Cassini spacecraft.

The image shows the heavily cratered Rhea in the foreground, while the hazy orb of the huge moon Titan looms in the distance. Cassini snapped the new Saturn moon photo in visible green light on Dec. 10, 2011, and it was released to the public on Feb. 13.

Cassini was about 808,000 miles (1.3 million kilometers) from Rhea and 1.2 million miles (2 million km) from Titan when it took the picture, researchers said.

Titan is the largest of Saturn's many satellites; at 3,200 miles (5,150 km) in diameter, it's nearly 50 percent wider than Earth's moon. The only moon in our solar system larger than Titan is Ganymede, which orbits Jupiter.

Titan has a thick, nitrogen-rich atmosphere that shrouds the frigid body in a soupy brown shroud. Complex organic molecules — the carbon-containing building blocks of life as we know it — swirl about in this atmosphere.

The huge moon also has a hydrocarbon-based weather system, with methane rain falling from the sky and pooling in liquid-methane lakes. Astrobiologists speculate that Titan may be one of the best places in the solar system to search for life beyond Earth.

Rhea is Saturn's second-largest moon, but it's a shrimp compared to Titan, measuring just 949 miles (1528 kilometers) across. As the new photo shows, Rhea's icy surface is battered and pocked with many craters.

Like Titan, Rhea has an atmosphere. But Rhea's is very different; it's much wispier and composed primarily of oxygen and carbon dioxide.

Researchers think the oxygen comes from Rhea's surface ice, liberated from water molecules that get blasted apart by charged particles streaming from Saturn's magnetosphere. The source of the carbon dioxide, however, is more mysterious.

Cassini launched in 1997 and arrived at Saturn in 2004. It has been studying the ringed planet and its many moons ever since, and will continue to do so for years to come. Last year, NASA extended the probe's mission to at least 2017.

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Photos: Best of Cassini

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  1. Starring Saturn

    This backlit view of Saturn was voted the favorite image to come from the Cassini orbiter - and it has been described as "perhaps the most stunning photograph ever taken." The image, captured on Sept. 15, 2006, shows two faint rings that were discovered by the Cassini team. And at the highest resolution, Earth itself appears as a pale blue dot just to the left of the brightest rings, at about the 10 o'clock position. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  2. Dark rings

    An infrared image from the Cassini orbiter, acquired May 24, 2007, reveals clouds beneath the hazes in Saturn's atmosphere, as well as the unilluminated side of the giant planet's rings. The shadows of the rings fall upon the planet's cloud layer. This image shares the honors as the favorite black-and-white picture from Cassini. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  3. Abstract art

    A Cassini image from May 10, 2006, shows the shaded edge of Saturn's disk, rounded by dark rings seen nearly edge-on. The crescent disk of Titan, Saturn's largest moon, can be seen in the background beyond the rings. This image shares the honors as the favorite black-and-white image from Cassini. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  4. Pearly moons

    Two of Saturn's moons - Tethys and Enceladus - look like pearls backdropped by the planet's disk in this image, captured on July 24, 2007. The thin "string" connecting the pearls is actually the plane of the planet's rings, seen edge-on. The rings cast a dark shadow on Saturn's disk. Two other moons appear in this image, although they can barely be made out at the highest resolution: Hyperion is near the lower left corner of the image, and Epimetheus is the slightest of specks between Tethys and Enceladus. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  5. Saturn from on high

    The Cassini spacecraft provides a high-contrast view of Saturn and its rings, as seen from above. This portrait is actually a mosaic of 36 images taken on Jan. 19, 2007, from about 40 degrees above the plane of the rings. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  6. Shadows on clouds

    Saturn's darkened rings cast shadows on the planet's blue and gold cloud tops, while the moon Dione hangs like a dot in the black sky beyond. This image was taken by the Cassini spacecraft on Feb. 4, 2007, from a distance of about 800,000 miles. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  7. View from below

    Cassini coasts beneath giant Saturn, staring upward at its gleaming crescent and icy rings. A great bull's-eye pattern is centered on the south pole, where a vast, hurricane-like storm spins. This view, obtained on Jan. 30, 2007, looks toward the lit side of the rings from about 26 degrees below the ring plane. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  8. Pastel planet

    Dark and sharply defined ring shadows appear to constrict the flow of color from Saturn's warmly hued south to the bluish northern latitudes. Scientists studying Saturn are not yet sure about the precise cause of the color change from north to south. The different colors may be due to seasonal effects on the atmosphere. The images that went into this mosaic were obtained by the Cassini spacecraft on Feb. 4, 2007. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  9. Ringing success

    This ultraviolet image from the Cassini spacecraft shows the detailed composition of Saturn's outer C and inner B rings from left to right, with the inner B ring beginning a little more than halfway across the image. The general pattern is from "dirty" red particles to the denser ice shown in turquoise as the ringlets spread outward. (University Of Colorado, LASP / AP) Back to slideshow navigation
  10. A is for amazing

    This ultraviolet image shows the A ring, beginning with a 'dirty' interior of red followed by a general pattern of more turquoise as it spreads away from the planet, indicating a denser material made up of ice. The red band roughly three-fourths of the way outward in the A ring is known as the Encke gap. (University Of Colorado, LASP - NASA / Reuters) Back to slideshow navigation
  11. Casting a shadow

    This image taken by Cassini shows the planet Saturn casting a shadow over its rings. (NASA - JPL - Caltech / Reuters) Back to slideshow navigation
  12. Titan revealed

    This is an infrared image of Titan, one of Saturn's moons, mapping the surface hidden beneath the moon's opaque atmosphere. Green areas represent water ice, while yellow areas have higher concentrations of hydrocarbons. The white spot is a methane cloud. (NASA) Back to slideshow navigation
  13. Ripples in the ring

    Scallops in the ring on the left side of this image were likely caused by a Saturnian moon rolling along the edge. One bright ringlet is visible within the gap, and at least one other faint ringlet can be made out. "This is textbook ring physics, right there, in one image," says Cassini imaging team leader Carolyn Porco. (NASA - SSI) Back to slideshow navigation
  14. Wisps in space

    A close-up of one of Saturn's rings shows a wispy pattern of ripples that may have been stirred up by a moonlet's orbit. Such unprecedented views of ring details are possible because of the Cassini camera's resolution. (NASA TV) Back to slideshow navigation
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  1. NASA / JPL / Space Science Institute
    Above: Slideshow (14) Best of Cassini
  2. Image:
    Y. Beletsky / ESO
    Slideshow (12) Month in Space: January 2014

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