Fields of five-story-high ice blades could complicate landing on Jupiter moon

Scientists have long wanted to explore Jupiter’s frozen moon, Europa, which is home to a vast subsurface ocean that makes it a promising home for extraterrestrial life. Recently, that desire has gained prominent financial backing from the U.S. Congress, which has directed NASA to start to build a robotic lander to follow the Europa Clipper, which will chart the moon from above.

But such a mission could be tricky. Probes have shown that Europa’s ice-bound surface is riven with fractures and ridges, and new work published today in Nature Geosciences suggests any robotic lander could face a nasty surprise, in the form of vast fields of ice spikes, each standing as tall as a semitruck is long.

Such spikes are created on Earth in the frigid tropical peaks of the Andes Mountains, where they are called “penitentes,” for their resemblance to devout white-clad monks. First described by Charles Darwin, penitentes are sculpted by the sun in frozen regions that experience no melt; instead, the fixed patterns of light cause the ice to directly vaporize, amplifying minute surface variations that result in small hills and shadowed hollows. These dark hollows absorb more sunlight than the bright peaks around them, vaporizing down further in a feedback loop.

Penitentes have already been seen on Pluto. And by calculating other competing erosional processes on Europa, such as impacts and charged particle bombardment, the new work suggests the vaporization of ice would be dominant in its equatorial belt, forming penitentes 15 meters tall spaced only 7 meters apart. Such formations could explain, the authors add, why radar observations of the planet dip in energy at its equator, the penitentes scattering the response. But the ultimate proof of whether Europa’s belly will be off limits to landing will come when the Clipper arrives in the mid-2020s.