Since entering Saturn's orbit on June 30 last year, the Cassini spacecraft has sent back intriguing images of some of the planet's 34 known moons. Newly released pictures from Cassini's first encounter with one such moon, Hyperion, indicate that the irregularly shaped satellite resembles a heap of rubble.

Hyperion's strange shape is immediately apparent in the images, which were taken between June 9 and 11 from distances between 168,000 and 815,000 kilometers away. Relatively fresh-looking craters pock the far-from-spherical surface, suggesting that large impacts have chipped away at the satellite. Because preliminary measurements suggest that Hyperion is only about 60 percent as dense as solid ice, NASA scientists posit that up to 40 percent of its interior is likely empty space.

Next on Cassini's agenda is another investigation of the moon Enceladus. The planned flyby on July 14 is the closest one yet for Cassini--the craft will come within 175 kilometers of the moon. The encounter should allow scientists to gather more information about the dust particles that they first detected in Enceladus' atmosphere during an April 26 flyby, which could deepen their understanding of Saturn's E ring. Then, on September 26 Cassini will get a closer look at Hyperion when it passes within 510 kilometers of the spongy moon.