NASA Spacecraft Snaps Last Close-Up Photos of Icy Saturn Moon

NASA's Cassini spacecraft has taken its last closeup photos of the icy Saturn moon Rhea. — This raw image of Saturn's icy moon Rhea was taken on March 10, 2013 by NASA's Cassini spacecraft, and received on Earth March 10, 2013. The camera was pointing toward Rhea at approximately 174,181 miles (280,317 kilometers) away. (Image credit: NASA/JPL/Space Science Institute)

NASA's Cassini spacecraft has snapped its last up-close photos of Saturn's icy moon Rhea, revealing a battered satellite covered in craters from violent impacts.

Cassini took the amazing new photos of Rhea on Saturday (March 9) during its fourth and final planned encounter with the Saturn moon. During the encounter, the probe flew within just 620 miles (997 kilometers) of Rhea, which is Saturn's second-largest satellite."Take a good, long, luxurious look at these sights from another world, as they will be the last close-ups you'll ever see of this particular moon," Cassini imaging team lead Carolyn Porco, of the Space Science Institute in Boulder, Colo., said in a statement accompanying the photos.

This image was taken on March 09, 2013, and received on Earth March 10, 2013, by NASA's Cassini spacecraft. The camera was pointing toward Rhea at approximately 1,727 miles (2,779 kilometers) away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. (Image credit: NASA/JPL-Caltech/Space Science Institute)

Saturday's flyby was designed primarily to measure Rhea's gravity field, mission scientists said. But Cassini also managed to take 12 pictures of the frigid moon's battered, pockmarked surface, including one that showcases a mysterious long, curving fracture called a graben.

This raw, unprocessed image of Rhea was taken on March 9, 2013 and received on Earth March 10, 2013. (Image credit: NASA/JPL-Caltech/Space Science Institute)

Rhea is the second-largest of Saturn's 60-odd known moons, with a diameter of 949 miles (1528 km). It's far smaller than the ringed planet's biggest natural satellite, Titan, which at 3,200 miles (5,150 km) across is nearly 50 percent wider than Earth's moon.

Rhea was discovered in 1672 by the mathematician and astronomer Giovanni Domenico Cassini, who gave his name to the NASA mission currently studying the Saturn system.

In 2010, researchers determined that the moon has a wispy atmosphere dominated by oxygen and carbon dioxide. The oxygen likely was blasted free from water ice on Rhea's surface by charged particles streaming from Saturn, scientists say, but the origin of the carbon dioxide is more mysterious.

The Cassini mission — a joint effort involving NASA, the European Space Agency and the Italian Space Agency — 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 on an extended mission until at least 2017.

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Michael Wall is a Senior Space Writer with Space.com and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.