Pluto Has Dunes Made of Ice Instead of Sand

It has been almost two years since NASA’s New Horizons probe made its historic flyby of Pluto, but we’re still learning new things about the dwarf planet from this mission’s data. Scientists were initially surprised to see the complex geology of Pluto, with ice mountains and vast frozen plains. It looks almost like a colder version of Earth in places. Now, researchers from the University of Plymouth in England say Pluto has another thing in common with Earth. Pluto has a system of dunes, but they’re not made from sand.

The study from lead author Matt Telfer focuses on photos taken of the Sputnik Planitia region of Pluto. You might not know this region by name, but you’ve seen plenty of photos of it. Sputnik Planitia forms the left side of Pluto’s famous “heart” feature. This expanse is composed of nitrogen ice,

Telfer and his colleagues examined Sputnik Planitia in detail, finding a region of distinctive ripples, the dunes of Pluto which you can see in the image above. This section of the plateau is about 47 miles (75 kilometers) wide and meets up with the Al-Idrisi Montes mountain range. Unlike Earth mountains, these are composed entirely of water ice.

The team considered that the dunes might be sublimation pits — areas of Sputnik Planitia where the sun caused frozen material to transition from solid directly to gas. However, the spacing and orientation rule out sublimation pits. So, it’s fair to call these dunes, but what are they? There’s no surface rock on Pluto that could produce sand. The grains that form the dunes are most likely tiny particles of frozen methane that come from that nearby Al-Idrisi Montes mountain range. The team suggests flecks of nitrogen ice from Sputnik Planitia itself are also an outside possibility.

Pluto, as imaged by New Horizons

Dune systems like those on Pluto turn out to be common throughout the solar system. We’ve found them on Mars, Venus, and Saturn’s moon Titan. Still, no one expected to find them on Pluto, which has an incredibly thin atmosphere. The atmosphere, composed mainly of nitrogen with hints of methane and carbon monoxide, is 100,000 times thinner than Earth’s. Telfer says the math works, though. The wind on Pluto has enough force to slowly organize loose particulates into dunes like those seen at the edge of Sputnik Planitia.

Unfortunately, New Horizons isn’t around to study the dunes further. Its mission was just a flyby for the probe, which has since headed out into the Kuiper belt where it will study smaller, more distant objects.