Pluto’s Sputnik basin tilted the entire planet

Enlarge / The formation, filling, and rotation of Sputnik Planitia. (credit: James Tuttle Keane)

The cliché is that a picture is worth a thousand words. But if you pay attention to all the information that scientists have extracted from New Horizons' photos of Pluto, then you'd be forgiven for thinking that's a gross under-estimate. Items large and small, from massive nitrogen seas to the mountain-sized icebergs that float above them, all provide hints of the geology of the alien world. And, even as more images were being sent back to Earth, planetary scientists pored over the ones we had, cataloging fault lines and pondering chemical traces.

Through their work, a picture of a dynamic world has gradually emerged. And now, two research teams have described the results of a careful look at Sputnik Planitia (formerly Sputnik Planum), Pluto's largest feature. They both find that a complex interaction between gravitational mechanics and Pluto's atmosphere likely resulted in Sputnik Planitia dragging the entire dwarf planet's axis of rotation around. And the fact that this happened reinforces earlier hints of an under-surface ocean filled with liquid water.

Sputnik Planitia is a giant basin filled with nitrogen ice. At the conditions on Pluto's surface, this ice is even more dense than water, allowing huge blocks of water ice to "float" on the surface. Yet it's also ductile enough that the entire basin is probably slowly mixing, driven by only the heat released by radioactive decay in Pluto's core. It's also expected that the basin is fed by a nitrogen cycle, as the gas sometimes sublimates off or re-condenses (there are also nitrogen glaciers feeding in from the nearby mountains).