Recovery of Microbes from Subsurface Europa Analog Environments: An Efficient Mechanical-Thermal Probe for Collecting Biological Samples from the Subsurface of Icy Moons.

Abstract

The ultra-low temperatures (<173K) and ultra-low pressures (<0.1 Pa) that exist on the surface of icy moons present a formidable challenge for collecting biological samples. Standard drilling technology is not efficient in these conditions, where conduction of thermal energy leads to the possibility of freezing in place and shear forces impart a strenuous test on microbial viability. If microbes exist within the first few meters of the surface, an extraction process must be gentle enough to recover them intact. This report describes a substantial improvement from the study by Davis in 2017, who presented a concave conical thermal probe capable of penetrating -65°C ice in 1000 Pa pressure. The current report describes a mechanical-thermal device for penetrating ≤ -150°C ice in 10 Pa pressure, which is analogous to the physical conditions on the surface of icy moons. The mechanism has an efficiency of >68% with -65°C ice and >61% with -150°C ice, which is well above the expected 10-15% for a Philberth-type probe. In addition, the probe can harvest a sensitive bacterium (Escherichia coli) from under a layer of acidified peroxide ice (pH 1.1), which is analogous to the expected surface chemical composition of the icy moon Europa. In field tests at -20°C air and -6°C ice temperatures, multiple organisms were extracted in a viable state, and chemical analysis indicated high-resolution separation of stratified layers. Finally, attaching the thermal tip to a telescopic mechanism allowed the probe to penetrate through 1.0 m of -65°C ice, which is well below the depth of harmful radiation expected at the subsurface of Europa. The current work opens the door for a lander vehicle to penetrate the upper subsurface of Europa and analyze biologically active samples.