Exploring Jupiter’s moon Europa will be a treacherous task, it seems: scientists reckon its surface is covered in sharp towering icy daggers. The menacing shards are known as penitentes, according to a paper published in Nature Geoscience this week. On Earth, these structures have been spotted pointing in the direction of the sun in the Andes and can reach up to five meters tall. Researchers from Cardiff University in the UK, and the NASA Ames Research Center and the University of Virginia in the US, estimate that conditions on Europa can nurture the growth of penitentes to almost 15 metres or...