A new laboratory study led by the University of Washington in Seattle (United States) and the Freie Universität in Berlin (Germany) shows that individual ice grains ejected from these planetary bodies may contain enough material for instruments directed there In autumn they detect signs of life, if it exists. The study is published in Science Advances.
“For the first time we have shown that even a small fraction of cellular material could be identified using a mass spectrometer on board a spacecraft,” summarizes lead author Fabian Klenner, a postdoctoral researcher at the University of Washington in earth and space sciences. “Our results give us more confidence that, using upcoming instruments, we will be able to detect Earth-like life forms, which we increasingly believe could be present on moons with oceans,” he adds.
The Cassini mission that ended in 2017 discovered parallel cracks near the south pole of Saturn’s moon Enceladus. Columns containing gas and ice grains emanate from these cracks. NASA’s Europa Clipper mission, scheduled to launch in October, will carry more instruments to explore Jupiter’s icy moon, Europa, in even more detail.
To prepare for that mission, researchers are studying what this new generation of instruments might find. It is technically prohibitive to directly simulate ice grains flying through space at 4 to 6 kilometers per second to impact an observation instrument, as the actual collision speed will be. Instead, the authors used an experimental setup that sends a thin beam of liquid water into a vacuum, where it disintegrates into droplets. They then used a laser beam to excite the droplets and mass spectral analysis to mimic what the space probe’s instruments will detect.
The newly published results show that instruments planned for future missions, such as the surface dust analyzer aboard the Europa Clipper, can detect cellular material in one of hundreds of thousands of ice grains.
The study focused on Sphingopyxis alaskensis, a bacteria common in waters off Alaska. While many studies use the Escherichia coli bacteria as a model organism, this single-celled organism is much smaller, lives in cold environments, and can survive with few nutrients. All of these things make it a better candidate for potential life on the icy moons of Saturn or Jupiter. “They are extremely small, so in theory they are able to fit into ice grains emitted from an ocean world like Enceladus or Europa,” explains Klenner.
The results show that the instruments can detect this bacteria, or parts of it, in a single grain of ice. Different molecules end up in different ice grains. The new research shows that analyzing individual ice grains, where biomaterial can be concentrated, is more successful than averaging a larger sample containing billions of individual grains.
A recent study led by the same researchers showed evidence of phosphate on Enceladus. This planetary body now appears to contain energy, water, phosphate, other salts and carbon-based organic material, making it increasingly likely to host life forms similar to those found on Earth.
The authors hypothesize that if bacterial cells were enclosed in a lipid membrane, like those on Earth, they would also form a skin on the ocean surface. “Here we describe a plausible scenario for how bacterial cells can, in theory, become incorporated into the icy material that forms from liquid water on Enceladus or Europa and is then emitted into space,” Klenner clarifies.
The surface dust analyzer aboard the Europa Clipper will be more powerful than instruments on previous missions. This and future instruments will also be able to detect negatively charged ions for the first time, making them more suitable for detecting fatty acids and lipids.
“With the right instrumentation, like the surface dust analyzer on NASA’s Europa Clipper space probe, it could be easier than we thought to find life, or traces of it, on icy moons,” concludes lead author Frank Postberg, professor of planetary sciences at the Freie Universität Berlin.