Ocean Moons: How can life be discovered?

Are there extraterrestrial life forms under the ice of Enceladus or Europa? The researchers report that answering this question may be easier than previously thought. Their experiments show that the probes can detect traces of potential life in individual ice particles that the icy moons expel from their liquid interior. Scientists say that the technical equipment of the planned missions could already provide good opportunities for astrobological research on mysterious ice moons.

They are considered promising candidates in the search for extraterrestrial life in our solar system: Saturn's moon Enceladus and Jupiter's moon Europa appear at first glance like dead balls of ice. But various studies have now shown that there may be potential habitats inside. Accordingly, oceans of liquid salt water hide under the moons' thick ice sheets. They are heated due to the gravitational effects of Saturn and Jupiter. Given the evolution of terrestrial life, it seems possible that organisms also appeared in these subglacial oceans. But can you clarify whether this is the case?

Icy fountains on the horizon

Examining material being ejected into space from cracks in the moon's ice could provide opportunities for this. Some of this water is frozen water that comes from the liquid interior and is pushed out through thermodynamic processes. There is already evidence of such fountains of water ice near Europa, and in the case of Enceladus, it has already been proven: NASA's Cassini mission, which visited Saturn's moon in 2017, discovered roughly parallel cracks on its surface. From there, gases and ice particles flow from the liquid depths of the moon into space. The Cassini probe's “Cosmic Dust Analyzer” has already been able to detect certain minerals in this material that appear to be important for the emergence of life.

The next planned mission is now targeting Europa: NASA's “Europa Clipper” space probe is scheduled to launch into the Jupiter system in October 2024 and then fly by Europa. On board will be the SUrface Dust Analyzer, which has better analytical capabilities than previously used tools. This concept is based on mass spectrometry tests of captured ice particles. Researchers led by Fabian Kleiner of the University of Washington have experimentally explored the potential the technology has already for detecting life.

To simulate how the probe would analyze captured ice particles, scientists first recreated them experimentally. To do this, a thin jet of water was injected into a vacuum chamber. It breaks down into tiny droplets that form particles consistent with particles captured on probe missions. The researchers then shot them with a laser. The charged particles were then examined in a mass spectrometer in the laboratory.

As a model for a form of life that might exist in the waters of icy moons, the team chose a bacterium found in Alaskan waters: Sphingopyxis alaskensis, which is particularly small, lives in an icy environment and survives on few nutrients. Researchers say such microbes could theoretically exist on icy moons. During the experiments, molecules containing bacteria or simply components of their cells were formed and examined.

Possibility of evidence of life

As the team reported, their analyzes show that instruments intended for future space probes could effectively detect substances typical of life, such as some fatty acids. The researchers found that even if just one percent of a cell's components is contained in a 15-micrometer-diameter ice grain, it is possible to detect bacterial signatures in the analysis data. “We have been able to document the possibility of detecting bacterial cell material using a mass spectrometer on board a space probe. “So it may be possible to detect small life forms on icy moons that are similar to those we know from Earth,” Kleiner concludes. Free University of Berlin: “With tools like the SUrface Dust Analyzer on NASA's Europa Clipper spacecraft, finding life or its traces on icy moons may be easier than previously thought.”

The researchers also show a possible mechanism for how traces of life could reach the material of the fountains: possible microbes may form a thin layer in areas of cracks attached to the surface. There, the pressure difference compared to the vacuum of space can cause cold water to boil, causing bubbles containing the cargo to rise. “This is a plausible scenario for how bacteria could be trapped in ice particles that form from liquid water on Enceladus or Europa, and then be ejected into space,” Kleiner says.

Source: University of Washington Specialized article: Science Advances, doi: 10.1126/sciadv.adl0849

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