Jupiter's frozen moon Europa has a massive ocean below the surface that could potentially harbor life. To find out, NASA is in the early stages of building a robotic lander to explore the moon in the mid-2020s. Now though, Cardiff University researcher Daniel Hobley and colleagues suggest that touching down on Europa could be tricky due to fields of massive ice spikes jutting up as high as 50 feet. From Science:
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.
From the research paper in the scientific journal Nature:
We estimate that penitentes on Europa could reach 15 m in depth with a spacing of 7.5 m near the equator, on average, if they were to have developed across the interval permitted by Europa's mean surface age. Although available images of Europa have insufficient resolution to detect surface roughness at the multi-metre scale, radar and thermal data are consistent with our interpretation. We suggest that penitentes could pose a hazard to a future lander on Europa.