A Detective History
To reach their conclusion on an underground floating sea on Pluto, Dalle Ore's team first had to add a probable story that explained it. Pluto's color was their first clue. When New Horizons started returning pictures of Pluto, the red spots covering large parts of the world ran out of scientists. They were a clear sign that Plutois icy surface is not all water ice but contains other elements. Virgil Fossae was one of the particularly red features of Pluto's so-called Cthulhu region, the dark area to the left of Pluto's bright and famous heart. So the researchers looked at spectral information for the region, to learn what types of materials are present.
They found a strong sign of ammonia. But ammonia is easily broken by the sun's ultraviolet light and charged particles and by cosmic rays. So, according to the calculations, the researchers believe that the surface ammonia must be deposited over the last several years. It may sound like a long time for people who only existed a few hundred thousand years ago. But it is not terribly long in the geological sense.
Perhaps it is more important that the ammonia resides in a region that looks quite young, as the ice pattern around it still looks as if it has gone out of an ice population and has not been destroyed by meteors or the covered side.
And while neither clue is crucial alone, they make a much stronger argument. Ammonia mixed in water lowers its freezing point. Planetary scientists have long stated that a liquid sea with a healthy ammonia shaft ̵
Pluto's rugged appearance when New Horizon's first images have suggested that cryovolcanism is either a recent or ongoing activity on the dwarf planet. And active ice volcanoes require something under the Pluto's surface to be fluid or at least slushy, capable of squeezing and flowing through cracks to the surface.
The ammonia leaking to the surface can explain where ice-cold Pluto has kept underground underground reservoirs, perhaps even to this day.