A single, complete view of half the world was enough to teach us how these distant, frozen bodies work.
On July 14, 2015, NASA’s New Horizons flew by Pluto.
At a resolution of only 80 meters (260 feet) per pixel, Pluto was revealed at resolutions thousands of times better than Hubble.
Near the poles, we found cratered highlands: an old, level, icy surface.
That terrain gives way, towards the equator, to hilly, ice-covered regions with scarred markings.
Hills transition into mountains of ice, some of which rise more than a mile (1600 meters) high.
These mountains aren’t static and stable, but rather are temporary water-ice mountains atop a volatile, nitrogen sea.
The evidence for this comes from multiple independent observations.
The mountains only appear between the hilly highlands, after the edge of a basin rim, and young plains with flowing canals.
These young plains occur in Pluto’s heart-shaped lobe, which itself was caused by an enormous impact crater.
Only a subsurface, liquid water ocean beneath the crust could cause the uplift we then see, leaving the nitrogen to fill it in.
The observed gravitational anomaly under Sputnik Planitia further indicates a sub-surface ocean.
Over time, this crater loads with volatile ices, eventually causing the whole world to tip over.
The most frozen, distant known worlds are still active today.
Mostly Mute Monday tells the story of an astronomical object, mission, or phenomenon in images, visuals, and no more than 200 words.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.