Alien life could lurk just a centimetre beneath the surface of Jupiter’s icy moon Europa, say scientists.
The frozen world is the likeliest place in the solar system to harbour extra-terrestrial organisms.
And they could be much closer than we think, according to new research.
The mysterious moon has no atmosphere which means – unlike Earth – it is bombarded with high levels of radiation.
But despite this microbial fossils could survive for up to 10 million years – a mere one-to-three centimetres under the ice.
So NASA would not need to drill several metres into Europa’s hard crust to look for recognisable organic samples — an act presently beyond our capabilities.
Dr Tom Nordheim, an expert on the habitability of icy worlds, said: “These results indicate future missions to Europa’s surface do not need to excavate material to great depths to investigate the composition of material and search for potential biosignatures.”
His team found regions at medium-to-high latitudes on the moon will be the best places to look.
Nasa believes it will find extra-terrestrial life in the next two decades. It’s already planning two missions to Europa.
A fly-by called Europa Clipper could launch in 2022 – and be followed by a lander mission a few years later.
The moon is a bit smaller than Earth’s and hosts a liquid ocean beneath its icy crust – making it a prime target in the hunt for alien life.
Young regions at medium-to-high latitudes could be the best locations to look for such signatures – providing useful guidance for these missions, said Dr Nordheim.
Europa is immersed in harsh radiation – leading to fears a lander would need to drill several metres deep which would be impossible.
Objects in the solar system are bathed in radiation from the sun and large planets such as Jupiter.
But the largest doses come from galactic cosmic rays (GCRs) which stream in from faraway sources such as exploding stars.
Earth’s thick atmosphere protects life from these. But life on other worlds would not be so lucky.
Mars once had an Earth-like atmosphere but now it’s thin – and Europa has virtually none at all.
Both worlds therefore are bombarded by high levels of radiation, which could spell doom for any fossils that may have once existed on the worlds’ surfaces.
So Dr Nordheim and colleagues modelled the effect of these energetic particles blasting Europa’s surface.
They then compared these estimates with laboratory data on how quickly radiation destroys amino acids – the building blocks of life.
Dr Nordheim, of ther California Institute of Technology in Pasadena, said: ‘At mid-to-high latitudes amino acids could persist at detectable levels a mere 1 to 3 centimetres below Europa’s surface over a 10 million year time scale.’
They could also exist within 10 centimetres in other areas of both hemishpheres, he said.
But Dr Nordheim added: ‘At the more irradiated equatorial regions, however, this depth increases to several tens of centimetres.’
His team whose findings are published in Nature Astronomy said a future Europa mission might not need to dig too deeply to find signs of life – provided it knows where to land.
Dr Nordheim said: ‘Observations of Europa’s surface made with an orbiter or close-up fly-bys – like those of NASA’s planned Europa Clipper mission – will be key to identifying such regions.’
Clipper will carry a payload of nine instruments including a camera that will image most of the surface.
Spectrometers will be used to scan its composition, ice-penetrating radar to map the shell in 3-D and find liquid water and a magnetometer to characterise the ocean.
Dr John Cooper, of the NASA Goddard Space Flight Centre in Maryland, says a lander should either probe deeper than ten centimetres wherever it lands or else do shallower measurements at high-latitude sites.
Dr Cooper, who was not involved in the study, said: “The lander itself would be the final judge of whether we have been clever or lucky enough to find a biosignature – perhaps one taking refuge from radiation within reach under a small block of ice, a sign of life we might most probably recognise as coming from our closest extraterrestrial cousin in the Universe of life.”