Nitrogen Glaciers on Pluto Studded with Water-ice Hills

The King of the Kuiper Belt Objects continues to deliver its secrets, data bit by data bit as the New Horizons spacecraft slowly radios its mother lode of science from the July 14th flyby back to Earth. The latest thing it’s showing us is a series of chunky hills made of water ice. They ride along on the nitrogen glaciers that cover Sputnik Planum. That’s the ice plain that we see at the “heart” of the heart-shaped Tombaugh Regio.

How Do Water Mountains Form on Pluto?

Okay, so we know that nitrogen ice dominates Pluto’s surface.  So, how do water-ice mountains get into the picture? It turns out they’re jabbing up from the Planum because of the differences between the two types of ice that are there. Water ice is less dense than the nitrogen-rich ice. That means that, like the way ice cubes float in a glass of water or iced tea, the water ice mountains are floating in a sea of frozen nitrogen. They’re moving more like icebergs do in Earth’s Arctic Ocean.

The next question is, if they’re floating like icebergs, where do they come from? The nearby water ice mountains ringing the Planum may provide clues. “Chains” of these drifting hills get in the way of the surface glaciers as they flow. Eventually some of the hills enter the cellular terrain of central Sputnik Planum. That’s when the motion of the nitrogen ice takes over and pushes them out to the edges of the surface cell. What New Horizons is showing us are 20-kilometer-long ice mountain “ranges” being shoved around by the action of nitrogen ice. Imagine a 20-kilometer stretch of the Colorado Rockies or the Himalayas being pushed around to get an idea of the geological action taking place on Pluto.

This is all incredibly exciting — one year after New Horizons formally began its “close fly-by” mission operations, it’s telling an amazing story about this world that is, by all rights, one of the most interesting planetary bodies in the solar system.