Pluto, our solar system's former ninth planet and current dwarf planet, has another surprise for us: landscape features seen on only one other planet—Earth.
Called "penitentes" after their resemblance of a crowd in kneeling penance, these icy spires can reach over 1,600 feet tall. Here on Earth, the same features are found in the Dry Andes above 13,000 feet, but they only grow to about 16 feet. Scientists suspected Europa might have these icy towers as well, but Pluto's the first world to show real evidence of them outside Earth.
In looking at photos taken by the New Horizons spacecraft in 2015, John Moores of York University, Toronto, and his team deduced how they formed. The spires are rather young, and formed by erosion. Penitentes need atmosphere to form, but Pluto's colder, thinner and darker atmosphere—combined with the ice forming from methane and nitrogen instead of water—allow these icy structures to stretch to fantastical heights as never seen before.
The signature of methane ice where the penitentes form on the Tartarus Dorsa mountains of Pluto is different from other parts of the surface, where ice is mostly nitrogen. This ice is transitioning straight from solid to gas, in a process called sublimation.
Fun fact: In Greek mythology, Tartarus is the lowest part of Hades where the wicked were thrown to suffer eternal torment—Pluto, of course, being the god of the underworld. So, we have a crowd of penitent people kneeling in the -400 degree frozen hellscape of Pluto's backside. Neat!
Moores' work is published in Nature. Watch Moores explain his findings, here:
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