Liquid nitrogen is still flowing on Pluto, three billion miles out
Key takeaways
- Dark features along northern Sputnik Planitia point to nitrogen reaching the surface as liquid
- The glacier's surface is probably under a million years old based on overturn modelling
- Pluto's surface temperature sits around minus 230 C, so something below is still supplying heat
- The study was led by Alan Stern, principal investigator on New Horizons
Pluto's surface sits at around minus 230 degrees Celsius. A study published in the Planetary Science Journal on 31 July found the first evidence of liquid recently flowing across it. The liquid is nitrogen.
Where the liquid nitrogen on Pluto shows up
The dark features sit along the northern edge of Sputnik Planitia, the nitrogen glacier that forms the left lobe of Pluto's heart. The glacier is larger than Texas and Oklahoma combined.
The team, led by Alan Stern of Southwest Research Institute and principal investigator on New Horizons, modelled nitrogen melting at the base of the ice. The melt then travels upward through narrow conduits and reaches the surface through cracks. The dark deposits are what it leaves behind.
The surface age is the detail that lands
Sputnik Planitia's surface is startlingly young. Overturn modelling puts it under a million years old, which on a four and a half billion year old body is essentially yesterday.
That is the detail that stops you. At minus 230 C, something beneath that ice is still producing enough heat to melt nitrogen and drive it up through the crust. Pluto was catalogued as a frozen relic for most of a century, and it keeps refusing to behave like one.
Why it matters
Geological activity this far out was not supposed to be on the list. Three billion miles from the Sun, with no tidal heating from a large parent planet, the expected state is dead and static. Sputnik Planitia is neither.
It also extends a run of results that keep pushing planetary formation and activity earlier and further out, including the youngest planet ever found around Elias 2-24.
What to watch
Whether anyone can put a heat source behind the model. Residual radiogenic heating and a subsurface ocean are both on the table, and the distinction matters for every other Kuiper Belt object of similar size. There is no follow up mission funded, so the next answer comes from reanalysis of New Horizons data rather than new observations. The next close look at the outer solar system depends on launch cadence, which is why Starship's first orbital attempt matters more to planetary science than it looks.
