Jupiter's moon Europa is one of the most fascinating worlds in our solar system, with its slushy subsurface ocean a promising place to look for extraterrestrial life. While NASA has plans to possibly send a lander to the moon in the coming years, a new discovery might make touchdown tricky – there's a chance that large swathes of Europa's surface are covered in ice spikes almost 50 ft (15 m) high.

The new study, led by researchers at Cardiff University, investigated some of the smaller-scale features that might make up the surface of Europa. The team calculated that the conditions on the moon might be perfect for creating structures called penitentes – tall, jagged blades of ice.

Penitentes form through the process of sublimation, where ice skips the liquid water phase and turns straight from a solid into gaseous water vapor. For that to happen, you need sustained sunlight and cold, dry air, so here on Earth they form in high-altitude tropical areas like the Andes in South America. There's even evidence of a penitentes presence on Pluto.

And Europa, with its icy surface and consistent sunlight, might be paradise for them. The researchers used observational data to determine how fast sublimation might occur across different parts of the surface, and then used that to estimate where any potential penitentes might form and how big they could get.

The team found that these spiky icicles could get as tall as 49.2 ft (15 m), which is about three times the size of Earthly penitentes. They'd likely be spaced about 24.6 ft (7.5 m) apart, and would tend to cluster around Europa's equator.

"The unique conditions of Europa present both exciting exploratory possibilities and potentially treacherous danger," says Daniel Hobley, lead author of the study.

But why haven't these penitentes been spotted directly? Europa has been fairly well-studied over the decades, from afar by telescopes like Hubble and from relatively close-up by Voyager in the 1970s and Galileo in the 1990s. Those observations have helped scientists find evidence of an underground ocean and plumes spraying the liquid water into space.

But, the team says, the resolution of these images hasn't been high enough to see surface features down to the scale of a few meters. Given the thermal conditions there, penitentes could therefore be hiding on Europa's surface, but that's far from confirmed at this point. Other scientists suggest that Europan ice has a very different composition to Earth's, which might affect its sublimation.

Either way, with NASA's Europa Clipper due for a flyby within the next decade, a much higher-resolution peek at the moon's icy surface should bring some answers.

The research was published in the journal Nature Geoscience.

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