The heart of Pluto has captured the imagination of millions thanks to the spectacular images from New Horizons. The heart, technically known has Sputink Planum, is also a unique geological feature, a nitrogen ice-ocean, and understanding its formation has kept scientists worldwide busy.
A new model, from French researchers at the French National Center for Scientific Research (CNRS), suggests exactly how the nitrogen ice got there in the first place. The heart is a large glacier formed inside a basin on the surface. And this new study suggests that Pluto’s atmosphere and the amount of sunlight it receives is favorable for the formation of nitrogen condensation, turning nitrogen gas into nitrogen ice and over thousands of years forming what we now call Sputnik Planum.
The study, published in Nature, modeled how the different physical processes work on Pluto. The team simulated the methane, nitrogen, and carbon monoxide cycles over thousands of years and looked at how the model differed from New Horizons’ data.
The results agree with what has been observed. A large nitrogen ice reservoir forms in the equatorial region, trapping carbon monoxide there, while the methane ice periodically covers both hemispheres.
Sputnik Planum contains most of the solid nitrogen that's present on the surface of Pluto, and it plays a crucial role in the Plutonian atmosphere. The frozen and volatile nitrogen are in equilibrium, so the amount of nitrogen in solid and gas form stays constant.
Nitrogen is not the only substance present, though. Small traces of carbon monoxide are also found in the heart, and methane frost is found all over the northern hemisphere except around the equator.
The key to the entire system is the solid-gas equilibrium of the nitrogen, which keeps the heart in shape. There is also another advantage to this new model – it doesn’t require an underground reservoir to explain how the nitrogen is maintained, as other studies had proposed.
The new research also suggests we are observing the peak of its atmospheric pressure. As Pluto moves further and further from the Sun, it will become lower and the seasonal frost will vanish in the next decades.