There is considerable international interest in the origin of life, both on Earth and icy worlds such as Europa, Enceladus, Ceres, and Titan. These ocean worlds may contain hydrothermal vents at the interfaces between their salty oceans and rocky cores and have been prioritized by NASA in the search for evidence of life in our solar system.¹ Hydrothermal vents on Earth have been shown to produce voltage and current in the field^2,3 and may be related to the origin of life.⁴ Electrochemistry certainly plays a role here, with hot reductants flowing from the crust and interacting with oceans through porous, partially conductive minerals. Understanding the natural systems that exist on Earth and may have contributed to the emergence of life, and determining similarities to hydrothermal vents on ocean worlds, is a critical step in exploring these unknown environments.

We have attempted to model these systems using both cyclic voltammetry and fuel cell experiments,⁵ with results presented here. While there is a plethora of potential redox couples which could be exploited in nature at hydrothermal vents, one of the most active reductants is H₂S, which is produced at many black smoker chimneys and reacts with various metals to generate compounds such as FeS and FeS₂, both of which are known electroactive materials. Studies on these materials indicate that they may produce energy which could be directly used by simple organisms on the outside of the chimneys and in turn feed larger organisms. This chain of energy utilization exists without solar irradiation, thus giving credence to the hypothesis that life may exist at the bottom of the ocean on the icy moons around Jupiter and Saturn.⁶

ACKNOWLEDGEMENT

The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) supported by JPL’s Research and Technology Development program.

References:

1. A. R. Hendrix et al., Astrobiology, 19 (2019).
2. R. Nakamura et al., Angew. Chemie Int. Ed., 49, 7692–7694 (2010).
3. M. Yamamoto et al., Angew. Chemie Int. Ed., 56, 5944 (2017).
4. G. Macleod, C. McKeown, A. J. Hall, and M. J. Russell, Orig. life Evol. Biosph., 24, 19–41 (1994).
5. L. M. Barge, F. C. Krause, J.-P. Jones, K. Billings, and P. Sobron, Astrobiology, 18, 1147–1158 (2018).
6. K. P. Hand, R. W. Carlson, and C. F. Chyba, Astrobiology, 7, 1006–1022 (2007).