Can you guess the subject of this photograph?

Here's a hint: it's big, gassy, and rhymes with pattern.

It's Saturn! Kind of. Technically, it's of Saturn's D-ring, the innermost (and faintest) ring encircling our solar system's second-largest planet. Via the Cassini mission's image page:

Can you guess the subject of this photograph?

Saturn's D ring may be faint and difficult to observe, but it rewards our patience. In this image, the Cassini spacecraft has captured some of the structure of the tenuous ring, appearing here as light/dark banding in the upper-right of the image. (The brightest ring material, in the lower-left here, is the C ring.) This banding, which is distinct from the vertical warping pattern Cassini scientists are monitoring (see A Twisted Tale), remains something of a mystery to scientists.

The vertical lines in this image are the tracks of stars. The D ring is so faint that long exposures are required to capture it and during the imaging the stars appear to move significantly due to the spacecraft's motion.

Read more over at the Cassini Photojournal.