Here's something you don't see every day -- or even every 15 years for that matter. These towering structures of ice and rock on the edge of Saturn's middle rings are an incredible and rarely captured sight visible only during the planet's equinox.
These structures rise as far as 2.5km out of the edge of Saturn's B ring, which has an average thickness of about 9m, and run for more than 1200km. They're believed to be the remnants of 1000m-wide moonlets that have broken up and been sucked into the swirling vortex of the planet's rings.
However, despite their size, these features are rarely seen. Only during Saturn's equinox, which happens once every 15 Earth years, does sunlight shines directly at the edge of the rings allowing them to cast shadow. This image was captured in 2009 by the Cassini space probe. We'll have to wait until 2024 to catch another glimpse.