A Thermodynamic Perspective on Potential Life in Icy Ocean Worlds

Our graduate Dr. Seda Işık conducted astrobiology research with an international team, providing valuable insights through a thermodynamic perspective in the search for life in the distant regions of the Solar System. The study was selected as a "Planetary Science Highlight" by NASA/JPL.

Dr. Seda Işık, who completed her doctorate at Istanbul Technical University (ITU) Eurasia Institute of Earth Sciences in the Earth System Science Program, achieved significant results in interpreting chemical evidence for the search for extraterrestrial life through her doctoral research conducted under the supervision of Asst. Prof. Dr. Nazlı Olğun Kıyak. The research was carried out with the participation of researchers from the NASA Jet Propulsion Laboratory (JPL/Caltech) and the Max Planck Institute for Solar System Research, and was supported by TÜBİTAK 1002.

The research aims to reveal the thermodynamic feasibility of chemical processes that could support life in the subsurface oceans of moons in the Solar System, defined as "icy ocean worlds."

"Energy Bottleneck" in ocean worlds similar to Earth's

It is thought to exist inner oceans on moons such as Jupiter's Europa and Ganymede, and Saturn's Enceladus and Titan, and that these oceans possess extreme conditions. The team used modeling to examine whether the Citric Acid Cycle (TCA/Krebs cycle), which plays a fundamental role in the metabolism of living organisms, could function under these extreme conditions.

The findings showed that some TCA intermediates (e.g., citrate, succinate) could form; however, the formation of compounds such as fumarate and oxaloacetate appeared to be thermodynamically unfavorable. This suggests that the cycle might require an external energy input to proceed. It is emphasized that a similar energy bottleneck has been observed in life-hosting environments on Earth, such as the Lost City Hydrothermal Field located along the Mid-Atlantic Ridge in the Atlantic Ocean.

The study also showed that prebiotic chemical processes could support this cycle, for example, simple organic molecules like pyruvate and acetate may remain stable. The reliability of the modeling results is enhanced by supporting data from both laboratory experiments and NASA’s Cassini mission.

The findings, selected as a "Planetary Science Highlight" by NASA/JPL, constitute a critical reference point for future space missions exploring icy ocean worlds in the Solar System. The results of this study aim to assist in the accurate interpretation of chemical composition data obtained from pioneering exploration programs (such as the European Space Agency's (ESA) JUICE mission, which will investigate Jupiter's moons Europa and Ganymede; NASA's Europa Clipper mission; and the Dragonfly mission to Saturn's moon Titan).

This research offers a valuable scientific contribution to the field of astrobiology, aiming to detect the chemical signatures of life not only on Earth but also in the distant and mysterious corners of the Solar System, thereby opening new horizons in this fascinating quest.

The study was published in the prestigious journal ACS Earth and Space Chemistry of the American Chemical Society. Access to the publication: https://doi.org/10.1021/acsearthspacechem.4c00371