Europa and the striking beauty of 50-foot-high ice blades

Daniel Hobley, a scientist at Cardiff University, and his colleagues used data from the Galileo spacecraft, a NASA mission that studied Jupiter and his moons between 1995 and 2003, to study sublimation rates on Europa. They discovered that in some parts of the moon, sublimation was overcome by other phenomena, such as a bombardment of tiny meteorites and particles coming from the space, which smooth the surface. But at the equator, conditions favored sublimation, which is the opposite.

To thrive, penitents need dry air, cold temperatures and prolonged exposure to the sun. The equatorial regions of Europa provide all three. Here, scientists conclude, an uneven terrain consisting of four-story spurs could emerge and survive.

These are of course only predictions. But they provide some of the richest descriptions of Europa's texture, one of the best candidates for extraterrestrial life in the solar system. The most powerful terrestrial and space telescopes, even Hubble, are not powerful enough to solve such surface details. The Galileo mission has produced some great cracks of ice crisscrossing the Europa ice, but only from a distance.

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"I hope this will add something to people's ability to imagine what they could see if they could actually walk to the surface – or, I guess, climb, given the peaks "said Hobley. "A bit of a search in Google images reveals some interesting visualizations of the surface, but these come from people assuming that everything would look like Antarctica and Greenland. We show that we can really think of this in a scientific way and that we could see something much more cool and more exotic. "

Cynthia Phillips, planetary geologist at NASAJet Propulsion Laboratory, hesitates to give too much weight to the predictions of researchers. She pointed out that the Galileo mission provided data on sublimation rates on a global rather than a regional scale. "It's a little exaggerated to extrapolate that far," says Phillips. "That said, it's the only information we have at the moment, so it makes sense to make a prediction and say, hey, these features are possible."

Such predictions are important if, as NASAyou are planning another trip to the Jovian system. The agency is preparing to send a spacecraft to Europa in 2020 to tour the moon dozens of times and study all kinds of features, from the icy surface to the depth of the ocean. The mission, known as Clipper, will be equipped with imagery technology that will track the ice axes at the equator of the moon, if they exist.

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Hobley and his research colleagues suggest that penitents on Europa could pose a danger to other types of spacecraft, like landers. NASA proposed a lander mission, but the concept is still under study. If penitents are actually crowded around the equator, engineers could easily avoid them by landing elsewhere.