The rings are the star of almost every picture of Saturn. But take a closer look and there's something mysterious about those pictures. Where are all the actual stars around the planet? Image: NASA/JPL/Space Science Institute
The stars are there, you just can't see them, and the reason why is the rings themselves. The rings of Saturn are incredibly bright -- in fact, they're brighter than most known stars. And that brightness comes at a cost.
When astronomers take photos of the planet with Cassini's Saturn-orbiting camera, including both the rings and stars in the same frame saturates the camera with too much light. To get just the rings, photographers can use a shorter exposure time, but that also means that the less-bright stars don't show up in the frame at all. Even pictures of Saturn's surrounding moons often end up with no stars in the frame because the moons also add to the overall brightness.
Cassini did manage to snag a picture of Saturn's moon Enceladus in 2008, with stars in the background, but only because the moon was in eclipse at the time.
Image: NASA/JPL/Space Science Institute