The Surface of Pluto Contains Methane Dunes Which Look A Lot Like Earth's Geography
So when a team of astronomers led by Matt Telfer of Plymouth University were examining some high quality images of Pluto taken by the New Horizons probe back in 2015, they were surprised to come across dunes scattered across the Plutonian landscape. Much like Earth dunes (or Mars dunes, which are fairly common), they form near mountain edges and run in the same directions as wind steaks.
But while dunes on Earth are large mounds of wind-blown sand, the dunes here on Pluto are made of methane instead. Since the surface of the dwarf planet can be as cold as -400 degrees Fahrenheit (-240 degrees Celsius), many substances which are gases on Earth turn into solids on Pluto - thus, you get mounds of solid methane.
Scientists discovered dunes and other Earth-like features on the dwarf planet Pluto. They said the dunes were surprising because it wasn't believed that Pluto's thin atmosphere could produce the wind needed to form them. pic.twitter.com/yQ3Y1xS33V— AJ+ (@ajplus) May 31, 2018
Again, it's not entirely clear how these dunes formed since wind comes from an atmosphere, and Pluto's hazy and nitrogen-filled atmosphere is extremely thin and tenuous. An atmosphere like that may create winds that can keep pushing sand-sized grains that were already in motion, but it shouldn't generate winds strong enough to start moving anything into a mound that large.
The team of astronomers have a slightly more complicated guess for how these methane dunes formed: methane and nitrogen ice frequently sublimes (or transforms from a solid into a gas) when warmed enough on Pluto's cold surface, and this process provides an upward force of motion that's enough to get the particles rolling enough for Pluto's light wind to keep pushing it.
And voila, Plutonian dunes of methane can form.
Since all we have are still images of Pluto, it's difficult to confirm that the dunes formed this way, but it's currently the best guess available. And just because it has dunes and an atmosphere still doesn't mean Pluto gets to be a planet again - it's just too small.