NASA's Cassini spacecraft is expected to complete its final close encounter with Hyperion, one of Saturn's many moons, on Sunday.

The probe will pass Hyperion at a distance of around 21,000 miles (34,000 kilometres) tomorrow, the US space agency said. However, images from the fly-by won't be beamed back to Earth until Monday at the earliest.

NASA said:

Mission scientists have hopes of seeing different terrain on Hyperion than the mission has previously explored in detail during the encounter, but this is not guaranteed. Hyperion (168 miles, 270 kilometres across) rotates chaotically, essentially tumbling unpredictably through space as it orbits Saturn.

Because of this, it’s challenging to target a specific region of the moon's surface, and most of Cassini's previous close approaches have encountered more or less the same familiar side of the craggy moon.

Hyperion's entire body is of such low density so-much-so that the edges of its craters are sharply defined, contributing to its odd, misshapen appearance.

The moon's gravitational field is subsequently very weak. Hyperion is also "quite porous", the mission's scientists have noted. ®