Shards of ice up to 15m (50ft) high on the surface of one of Jupiter's moon could cause problems for landing probes.
Europa is covered by an ice-encrusted ocean of salty water and could support life, scientists say.
The moon is high on the list for future interplanetary space missions, but a new study suggests landing probes may have to navigate around some tricky obstacles.
Scientists from the University of Cardiff say shards of ice up to 15m (50ft) high could be dotted all over the moon's surface.
Dr Daniel Hobley, from the University of Cardiff's school of earth and ocean sciences, said: "The unique conditions of Europa present both exciting exploratory possibilities and potentially treacherous danger.
"The presence of sharp, blade-like structures towering to almost 15 metres high would make any potential landing mission to Europa extremely precarious.
"We hope studies like ours will help the engineers to develop innovative ways of delivering landers safely on Europa's surface so that we can find out even more about this fascinating place, and potentially look for signs of extra-terrestrial life."
The shards, called penitentes, are sharp-edged blades, with spikes, that point toward the midday sun.
They form through a process which allows ice to turn into water vapour without turning into water first, called sublimation.
When ice sublimates, shards are left behind.
There are examples of smaller ice shards which have formed from sublimation on Earth, but these are restricted to high-altitude tropical and sub-tropical regions like the Andes.
On Europa, the conditions are perfect for giant penitentes to form.
The report is published in Natural Geoscience.
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