Fields of sharp ice growing to almost 15 metres tall could be scattered across the equatorial regions of Jupiter's moon, Europa, which may make the search for alien life difficult, scientists say.
Previous space missions have identified Europa as one of the likeliest destinations for harbouring life in our solar system, most notably because of the large seas of liquid water underneath its surface, said researchers from Cardiff University in the UK.
The new study, published in the journal Nature Geoscience, suggests that any potential landing mission may have to navigate hazardous obstacles known as 'penitentes' before touching down on Europa's surface.
Penitentes are tall sharp-edged blades and spikes made of snow and ice that point towards the midday sun. They form through a process known as sublimation, which requires bright, sustained sunlight as well as cold, dry and still air.
"The unique conditions of Europa present both exciting exploratory possibilities and potentially treacherous danger," said Daniel Hobley from Cardiff University's School of Earth and Ocean Sciences.
Penitentes are present on Earth and grow to between one and five metres tall, but they are restricted to high-altitude tropical and subtropical conditions, such as in the Andes.
Europa, however, has the perfect conditions necessary for penitentes to form more uniformly -- its surface is dominated by ice; it has the thermal conditions needed for ice to sublime without melting, researchers said.
There is very little variation in the angle in which the sun shines on the surface, they said.
The researchers used observational data to calculate the sublimation rates at various points on Europa's surface and thus used these to estimate the size and distribution of penitentes.
They concluded that the penitentes could potentially grow to around 15 metres tall with a spacing of around 7.5 metres between each one.
It was also inferred that the penitentes would be more common around Europa's equator.
No spacecraft has yet landed on Europa; however, NASA intends to undertake a number of flybys around the moon with the Europa Clipper, which will be launched in 2022. It is believed a landing mission could follow soon after.
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