A crater-coated moon called Dione is illuminated against the backdrop of Saturn and its rings in stunning new images captured by NASA's Cassini spacecraft.

The new images, taken during the spacecraft's final flyby of Dione last week, include two of the sharpest images ever taken of the surface of Dione, the fourth-largest among the dozens of known moons of Saturn.

Cassini passed within 474 kilometres of Dione's surface on Aug. 17. That wasn't its closest flyby, but reflected sunlight from Saturn made it possible to see details in the shadows of some of the images, said Tilmann Denk, a Cassini participating scientist at Freie University in Berlin, in a statement.

Saturn's moon Dione hangs in front of Saturn's rings in this view taken by NASA's Cassini spacecraft during the inbound leg of its last close flyby of the icy moon. This time, Cassini passed within 474 kilometres of Dione's surface. (NASA/JPL-Caltech/Space Science Institute)

The goal of the flyby wasn't imaging, but gravity measurements intended to gather clues about Dione's interior structure and the processes affecting its surface, NASA said. That meant the spacecraft was pointed in the direction that gave the best gravity measurements rather than the best pictures.

"We had just enough time to snap a few images," Denk said.

Dione hangs in front of Saturn and its icy rings in this view. Dione is about 1,120 kilometres in diameter – about a third the diameter of our own moon – and orbits around the same distance from Saturn as our moon from the Earth. (NASA/JPL-Caltech/Space Science Institute)

Dione is about 1,120 kilometres in diameter — about one-third the diameter of our own moon — and orbits around the same distance from Saturn as our moon from the Earth. It's the fourth-largest of Saturn's 62 confirmed moons.

After leaving Dione, Cassini will make three flybys of Enceladus, a moon known for its icy geysers, including one on Oct. 28 that will bring it just 49 kilometres from the surface.

As Cassini soared above high northern latitudes on Saturn's moon Dione, the spacecraft looked down at a region near the day-night boundary. This view shows the region as a contrast-enhanced image in which features in shadow are illuminated by reflected light from Saturn. (NASA/JPL-Caltech/Space Science Institute)

It will spend the next two years viewing Saturn's moons, both large and small, from a greater distance before diving 22 times through the space between Saturn and its innermost ring and then plunging into Saturn's atmosphere.

Cassini launched in 1997 with the European Space Agency's Huygens probe, with a mission to study Saturn, its rings and its moons. They arrived at Saturn in 2004 and the probe landed on Titan in 2005. The Cassini mission was supposed to end in 2008, but was later extended until 2017.