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Icy Worlds: Astrobiology at the Water-Rock Interface and Beyond

Click here to visit the JPL Icy Worlds website.

The NAI JPL team is pursuing an interdisciplinary and highly synergistic combination of experimental, theoretical, and field-based lines of inquiry focused on answering a single compelling question in astrobiology: How can geochemical disequilibria drive the emergence of metabolism and ultimately generate observable signatures on icy worlds? NASA has laid the Universe out before us all to reveal its self-organizing machinery, from the first ripples of inflation to black holes, to the moons orbiting the larger planets in our own Solar System. Yet the most complex of all self-organizing entropy-generating systems – life – is still only recognized here on our Earth. The JPL Icy Worlds team intends to demonstrate how the particular physical and chemical gradients operating at the rock-water interfaces in icy world oceans can drive the chemistry that leads to early metabolic pathways. With this knowledge, coupled with an understanding of the thermal, tidal and chemical disequilibria prevailing on icy worlds, it will be possible to make informed predictions as to their habitability or otherwise. This pioneering knowledge will feed into the development of mission concepts such as Europa Clipper and the LIFE sample return mission to Enceladus.

Astrobiology at water-rock interfaces found on icy bodies (e.g., Europa, Enceladus and Ganymede) in our Solar System (and beyond) is the unifying theme of the JPL Icy Worlds team. Several of the icy moons in our Solar System have subsurface oceans that, combined, contain many times the volume of liquid water on Earth. All of these icy worlds may host or may have once hosted water-rock interfaces generating energy from geochemical gradients. The JPL teams consists of an interdisciplinary team of researchers who will be working together to examine bio-geochemical/- geophysical interactions taking place between rock/water/ice interfaces in these environments to better understand and constrain the many ways in which icy worlds may provide habitable niches and how we may be able to identify them. In order to organize their approach to addressing the single compelling question stated above, the proposed research is structured around answering four key questions, each of which provides the focus of one of four detailed science investigations (INVs 1–4, respectively). Each investigation integrates information and results from the other investigations as depicted in Fig.1 and, collectively, address five out of seven goals listed in the NASA Astrobiology Roadmap. These key questions are:

• What geological and hydrologic factors drive chemical disequilibria at water-rock interfaces on Earth and other worlds?
• Can geoelectrochemical gradients in hydrothermal chimney systems drive prebiotic redox chemistry towards an emergence of metabolism?
• How, where, and for how long might disequilibria exist in icy worlds, and what does that imply in terms of habitability?
• What can observable surface chemical signatures tell us about the habitability of subsurface oceans?

INV 1 will aim to answer the Key Question: What geological and hydrologic factors drive chemical disequilibria at water-rock interfaces on Earth and other worlds? Geological environments that generate disequilibria are of interest for astrobiology, since all life as we know it lives off energy from disequilibria in the form of pH, redox and ionic gradients. In this investigation, the JPL team will examine water-rock interactions in the lab and in the field, to characterize the geochemical gradients that could be present at water-rock interfaces on Earth and other worlds, taking into account different ocean and crustal chemistries, and to inform INV 2.

INV 2 aims to answer the Key Question: Can geoelectrochemical gradients in hydrothermal chimney systems drive prebiotic redox chemistry towards an emergence of metabolism? In this investigation, the team will explore, in detail, a specific example of geochemical disequilibria at the water-rock interface. They will experimentally and theoretically evaluate how hydrothermal chimney systems can harness the energy provided by geochemical disequilibria, as occurs today in deep-sea vents that act as “environmental fuel cells” to power redox reactions. In addition, the Icy Worlds team will conduct experiments that simulate the energetic processes of a vent system—including ambient electrical potentials and proton gradients—and test whether these gradients can drive certain chemical reactions of interest to an emergence of metabolic pathways. These innovative studies will utilize modular fuel cell experiments to test out-of-equilibrium geological systems under a variety of possible icy world conditions.

INV 3 will answer the Key Question: How, where, and for how long might disequilibria exist in icy worlds, and what does that imply in terms of habitability? This investigation links the processes occurring at the water-rock interface addressed in INVs 1 and 2 with bulk ocean composition and ultimately, the observable surface chemistries studied in INV 4. The JPL team will develop models of icy world seafloor evolution and habitability, under extremes of temperature and pressure, including the first-ever application of recent breakthroughs in our understanding of fluid and mineral thermodynamics of Earth’s deep carbon cycle to icy worlds. Experimental measurements of fundamental properties specific to fluids in icy world oceans will be used to extend our insights about water-mineral evolution into the fluid regime and endow the already powerful FREZCHEM modeling software with the ability to model deep icy world oceans.

INV 4 will aim to answer the Key Question: What can observable surface chemical signatures tell us about the habitability of subsurface oceans? Answering this question will shed light on the evolution of ocean materials expressed on the surface of airless icy bodies and exposed to relevant surface temperatures, vacuum, photolysis and radiolysis. The JPL team will conduct an experimental program designed to establish the extent to which chemical compositions of icy world surfaces are indicative of subsurface ocean chemistry. Europa and other icy worlds containing vast global oceans beneath crusts of ice are key targets for understanding the impact of an extensive rockwater interface on a body’s habitability. This team’s research, therefore, will illuminate the connection between observables on the surface to the habitability of subsurface aqueous environments. These investigation will provide the means to interpret the data acquired by flyby, orbital, or in situ missions to icy worlds, and assess the potential habitability of these environments.

Figure 1. A graphical representation of the Icy Worlds investigations (INV). Arrows illustrate how these INVs are linked to each other.