The part of science I like best is that the more we learn, the more questions we have. Pluto provides a perfect example of this. Initially a planet, although lonesome. Then it found its kin, a set of dwarf planets. And now, when we actually see it, it looks more Earthly than we could have imagined. Large, frosty glaciers, seemingly draining watery residue from icy mountains. A distinct, hazy atmosphere, layered and complex. Active landscapes. This is absolutely not the dead cold planet we teach about. This enigma is alive.
In the photo, the New Horizon’s spacecraft is looking back at Pluto, with the Sun setting through the mist. The glaciers slowly drain moisture from icy mountains that tower over smooth, lowland basins. Overhead, the sky is filled with haze – lots and lots of it, carved into multiple layers. The image, “reminds me of the Transantarctic Mountains along the Ross Ice Sheet, because of the tall mountains looming over a flat open expanse of ever-changing ice,” says New Horizons team member Simon Porter of the Southwest Research Institute.
But there the similarity to Earth ends. Pluto’s mountains cannot be made by plate tectonics. Pluto’s glaciers are made from nitrogen, not water ice. Pluto has something analogous to Earth’s hydrological cycle, where water evaporates from the oceans, rains or snows back down, and returns to the seas by rivers and glaciers. But Pluto’s chemistry and temperature are different, perhaps dominated by soft nitrogen ice, and also featuring methane and carbon monoxide ices. This is not Earth-like. It is not reminiscent of Mars or Venus. This is not a planet.
To use the word ‘planet ‘ to describe this land is doing it a disservice. It is so much more than that. This, is an enigma.