Exploring Potential Signatures of Life on Ocean Moons

Published: 6 July 2023

A New Cross-Disciplinary Collaboration for Upcoming NASA Missions and Mission Concepts

Scientists have long been captivated by the possibility of discovering evidence for extraterrestrial life in the universe. While many of the world’s largest telescopes are pointed toward distant galaxies and star systems, some think there’s a strong possibility that life could be detected much closer to home.

In a new collaboration with a scientist at NASA’s Jet Propulsion Laboratory (JPL), Professor Nagissa Mahmoudi of the Department of Earth and Planetary Sciences is investigating potential biosignatures on two of our solar system’s moons: Europa, orbiting Jupiter, and Enceladus, orbiting Saturn. Despite thick layers of solid ice and dramatically low surface temperatures, scientists think that, under the surface, these water worlds could possess the right conditions to support microbial life.

It’s an unexpected avenue of research for Mahmoudi, a geomicrobiologist who studies how microbes interact with organic compounds in deep-sea environments on Earth. “The study of organic molecules in our oceans has revealed chemically stable compounds dating back thousands of years, thanks to microbial processes,” she explained. “Our hunch is that if there is life under the icy surfaces of these ocean moons, we may be able to detect it in the form of microbial byproducts.”

While the icy shells of Europa and Enceladus are thought to be up to tens of miles thick, both moons show signs of hydrothermal activity below the surface, which could create environments hospitable to life. Observations have also revealed at least 100 watery jets erupting from Enceladus, and there are indications that similar plumes may exist on Europa. An orbiting spacecraft could potentially pass through these plumes, researchers say, and analyze their icy particles. Doing so may provide new insights into chemical or even biochemical processes taking place deep below the icy surface.

With NASA’s Europa Clipper mission set to launch in 2024, Mahmoudi and her collaborator, JPL Research Scientist Morgan Cable, are working to test this theory using the same advanced scientific instrumentation that will be aboard the spacecraft when it departs Earth. (While no mission to Enceladus is currently in progress, the proposed Enceladus Orbilander mission concept envisions a potential departure in the 2030s.) If mission control knows what to look for, the thinking goes, it will help them determine which measurements to take – and how to interpret them – when the spacecraft arrives at its destination.

But what might alien microbial life look like, and how would we know if we found it? Working out of her lab in the Adams Building, Mahmoudi and her students are cultivating, under highly controlled conditions, a diverse range of different microbes found in deep-sea hydrothermal environments. These microbes could hypothetically appear in the oceans of Europa and Enceladus, given what is known and hypothesized about conditions on these gelid moons. Mahmoudi’s team will then isolate their metabolic byproducts – in other words, their ‘poop’ – to get a better sense of what these compounds might look like in a plume.

“The reason we’re looking at byproducts is that we know, at least in ocean environments on Earth, they are stable and stick around a lot longer than life itself,” Mahmoudi said. “For this reason, we think byproducts are ideal to explore as potential biosignatures, as they are more likely to persist in environments such as the plume of Enceladus or the surface of Europa. In addition, they are detectable with current instrumentation, including the instruments that will be aboard the Europa Clipper mission.”

Next, these samples will be shipped off to Cable’s lab at JPL for analysis with mass spectrometry to gain a deeper understanding of their chemical profiles. Using technology available at Caltech and JPL, Cable will replicate a close flyby of Europa by the spacecraft, creating icy particles sputtered from the moon’s surface or emitted via a plume and impacting them at spacecraft flyby velocities (~3 km/s). By analysis of the post-impact products in the same way as the Surface Dust Analyzer instrument aboard Europa Clipper, Cable and Mahmoudi will test whether the scientific payload will be capable of detecting and distinguishing these microbial byproducts’ unique chemical signatures.

If the team can isolate distinct chemical ‘fingerprints’ for life and confirm the possibility of measuring them in upcoming missions and proposed mission concepts to these watery moons, the implications could be profound. “This is a new avenue for my research, and I’m excited to see where it goes,” Mahmoudi said. “It’s a thrill to work on such a fundamental mystery, and I hope our proposed work helps us develop a better understanding of the possibilities for extraterrestrial life in our universe.”

Mahmoudi and Cable’s collaboration emerged at a recent meeting of the Scialog – Signatures of Life in the Universe Initiative, sponsored by the Heising-Simons Foundation and the Research Corporation for Science Advancement. The gathering brought together some 50 early-career scientists from a wide range of disciplines to exchange ideas on developing new approaches to the search for extraterrestrial biosignatures. In a breakout room during the meeting, Mahmoudi and Cable started a casual discussion about the potential for deep-sea research on Earth to advance understanding of biosignatures on Europa and Enceladus. Before the end of the meeting, they had written up a joint proposal and pitched it to the event sponsors, which awarded them a one-year grant to pursue their novel research.

Learn more about the event and the supported research at the Scialog website.







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