Imma Perfetto
Cosmos science journalist
Jupiter’s moon Europa and Saturn’s moon Enceladus probably harbour vast oceans under their icy crusts. Could life survive within them?
A new NASA experiment suggests that, if these oceans support life, organic molecules like amino acids and nucleic acids could survive just under the ice’s surface.
The findings have implications for sampling depths and locations in future life detection missions to Europa and Enceladus.
“Based on our experiments, the ‘safe’ sampling depth for amino acids on Europa is … [about] 20cm at high latitudes of the trailing hemisphere (hemisphere opposite to the direction of Europa’s motion around Jupiter) in the area where the surface hasn’t been disturbed much by meteorite impacts,” says Alexander Pavlov of NASA’s Goddard Space Flight Center in the US, lead author of the paper published in Astrobiology.
“Subsurface sampling is not required for the detection of amino acids on Enceladus – these molecules will survive radiolysis (breakdown by radiation) at any location on the Enceladus surface less than … a few millimetres from the surface.”
Radiation from space and high-speed particles in their planet’s magnetic fields bombard the surfaces of Europa and Enceladus, making it unlikely for life to survive there.
However, their subsurface oceans – heated by tides caused by the gravitational pull of nearby moons and the host planet – could provide the necessary energy supply and elements and compounds necessary to create biological molecules.
These biomolecules could be brought to the surface by geysers or the churning motion of the ice crust.
To determine the rates at which amino acids would break down, (known as “radiolysis constants,”) researchers simulated the conditions on these icy worlds. They mixed amino acids with ice at about -196° C in sealed, airless vials and bombarded them with varying doses of gamma-rays.
With this data they then used the age of the ice surface and the radiation environment at Europa and Enceladus to calculate the drilling depth and locations where 10% of the amino acids would survive radiolytic destruction.
The team found that amino acids degraded faster when mixed with silicate dust (simulating the potential mixing of material from meteorites) but degraded slower while still inside dead bacteria.
“Slow rates of amino acid destruction in biological samples under Europa and Enceladus-like surface conditions bolster the case for future life-detection measurements by Europa and Enceladus lander missions,” says Pavlov.
“Our results indicate that the rates of potential organic biomolecules’ degradation in silica-rich regions on both Europa and Enceladus are higher than in pure ice and, thus, possible future missions to Europa and Enceladus should be cautious in sampling silica-rich locations on both icy moons.”
