In images taken by NASA's New Horizons spacecraft when it flew past Pluto in July, scientists have spotted dendritic features that look as if they have been carved by liquids.
In the models, Pluto's atmosphere, wispy today at just 1/100,000th of the atmospheric pressure of that at sea level on Earth, fluctuated wildly over millions and billions of years.
At times, the pressure was dense enough that liquid nitrogen could exist on the surface, to flow as streams and pool as lakes.
"The ingredients that are there — none of them surprise us," said William M. Grundy, of Lowell Observatory in Arizona, who leads the team analyzing the composition of Pluto's surface on NASA's New Horizons mission.
At Pluto's ultrafrigid temperatures — minus-390 degrees Fahrenheit at the surface — water ice is rigid and unbending, like bedrock on Earth.
The varying mixes of ices could form different alloys with very different properties, similar to how adding carbon transforms iron into steel, and that could help explain the wide range of topography.
Nitrogen might also flow deep enough to be warmed by the interior and then erupt back at the surface — producing what scientists are surmising might be an ice volcano.
