NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

How Pluto got its heart of ice

New climate simulations help explain how Pluto’s heart-shaped Sputnik Planum (lower right) got its thick glaciers of nitrogen and carbon monoxide. Some of the glaciers, first seen by the New Horizons spacecraft in July, hold ice that circulates like the material in a lava lamp. Now, to find out how the glaciers formed in the first place, scientists created models that simulated atmospheric circulation on the dwarf planet for the last 50,000 years (a mere 200 orbits around the sun for Pluto). At the beginning of the simulations, the researchers gave Pluto a planet-wide veneer of nitrogen, carbon monoxide, and methane ices a few millimeters thick; then, the planet’s surface and atmosphere evolved as the icy orb passed through orbit after orbit. If Pluto were a completely smooth sphere, it would have either a permanent swath of nitrogen ice at the equator or seasonal snow caps at its poles. But that’s not what the planet looks like today. When researchers added realistic topography to the model, including the 4-kilometer-deep Sputnik Planum and two other large craters, the basin gradually trapped Pluto’s nitrogen, carbon monoxide, and much of its methane, the researchers report online today in Nature. That’s because the dwarf planet’s sparse atmosphere is thickest at lowest elevation, making condensation of the ices most effective there. Besides helping explain the current pattern of ices on Pluto’s surface, the new simulations also shed light on substantial changes in Pluto’s atmospheric pressure observed in recent years. The team’s models suggest that in the coming decade, the dwarf planet’s atmospheric pressure will decrease and the frosts now seen in Pluto’s northern hemisphere will disappear. If it happens, this will be a crucial verification of their model, the researchers say.