Regardless of whether penitentes are common - or unique to Earth and Pluto - the find on the dwarf planet shows some remarkable characteristics. Pluto's penitentes are made of methane ice, while on Earth they're composed of water ice. Pluto's are more widely spread apart than what we find on Earth, where Moores says graduate students have trouble clambering among the spikes. On Pluto, by contrast, it appears the features are separated by a couple of miles. So there's plenty of room to set down a lander if we wanted.
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What's more, the penitentes suggest that Pluto had calm atmospheric conditions over long periods of time, perhaps tens of millions of years. Regularly spaced and shaped penitentes, like what we see on Pluto, require an atmosphere; irregularly ones could develop where no substantial atmosphere is present, like Europa. Pluto's atmosphere expands and collapses as it gets further and closer from the sun in its nearly 248-year orbit. From numerical models, the team suggests that the penitentes could start growing (and continue developing) given warm enough atmospheric conditions for just a few years at a time.
"The winds on Pluto are really light, and there's only one period in every orbit where the atmosphere grows thick enough to control the creation of these types of features," Moores said. The active time right now is during the spring equinox, but Pluto's orbit has changed over the years; in the more distant past, penitentes best grew during the autumnal equinox, he said.
While Moores' team looks to other worlds for evidence of penitentes, they are also eagerly waiting for two Jupiter missions that will explore the icy moons - the proposed NASA Europa mission, and Europe's confirmed JUICE (JUpiter ICy moons Explorer). These missions are expected to visit Jupiter's system around the 2030s, focusing on Europa (in the Europa Clipper's case) and Ganymede (for JUICE).
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