Here's something you don't see everyday—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 1.6 miles out of the edge of Saturn's B ring, which has an average thickness of about 30 feet, and run for more than 750 miles. They're believed to be the remnants of kilometer-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.