The accumulation of ice in the coldest region of Pluto - the Sputnik Planitia within Pluto’s ‘heart’ - was inevitable, a study in this week’s Nature reports. Previous studies have suggested that the 1,000-kilometre-wide basin may have been caused by an impact, but the present modelling study instead suggests that the weight of the ice created the depression within the Sputnik Planitia. These findings add to our understanding of the evolution of Pluto’s heart.

Douglas Hamilton and colleagues run computer simulations that indicate that ice deposits would have concentrated into a single cap within one million years of the formation of Charon, one of Pluto’s moons. As frosts began to accumulate, the region would reflect more sunlight, making it colder and thus driving further deposition of ice, a phenomenon known as the runaway albedo effect. The weight of the ice caused the crust to slump, creating its own basin.

The authors add that the accumulation of ice in this region, along with tidal forces from Charon, caused Pluto to rotate such that the cap would be at a longitude directly opposite the moon. Finally, the authors propose that since its formation, the Sputnik Planitia ice cap has been stable, albeit gradually losing volume, over the age of the Solar System.