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Executive Summary

In this interdisciplinary research we conduct a 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?

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 for the proposed research. 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 free energy from geochemical gradients. Our transdisciplinary team of researchers are 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 our approach to addressing the single compelling question stated above, our 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).
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? In this investigation, we 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, we explore, in detail, a specific example of geochemical disequilibria at the water-rock interface. We 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. We 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. This innovative study 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. We 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? We 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. We 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 rock-water interface on a body’s habitability and habitancy. We will illuminate the connection between observables on the surface to the habitability of subsurface aqueous environments. This 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.

Below we provide a summary of our accomplishment since the start of this project on April 13, 2015:

Although INV1 has reduced carbon dioxide to formate in a matter of minutes in hydrothermal serpentinization experiments and we know nitrate can be reduced all the way to ammonia in 3 hours – nevertheless, using the same tunable diode laser spectrometer operated by MSL, we detected no methane in over 100 hours of hydrothermal operation (White et al., in prep.). This negative result has given us cause to rethink how the first pathway to carbon fixation was channeled and negotiated. Therefore, as a test of the alternative methanotrophic pathway – already considered by Shibuya et al. (2016) – we will, in conjunction with Investigation 2, attempt to oxidize hydrothermal methane to a methyl group with nitrate, involving green rust, greigite and mackinawite (White et al, 2015; Wong et al., submitted). And to further understand how such disequilibria can be converted and drive this type of metabolism we are collaborating with the NAI CAN6 University of Illinois Team “Towards Universal Biology” (Branscomb et al., in prep). Moreover, as we consider the hard steps to methane oxidation will involve electron bifurcation, with our collaborators in France we are investigating how the hydrogen bond network around the pyranopterins (cf., analogous H-bond behavior in the interlayers of green rust) controls redox-cooperativity in a molybdenum-bearing cofactor (Duval et al., submitted).

In INV 2, we have had a successful six months simulating hydrothermal environments in the laboratory analogous to early Earth and/or icy worlds. In the spring, Barge, Russell, and student intern Lily Abedian published a paper in Angewandte Chemie showing how prebiotic hydrothermal systems produce electrical potential and current, energy to “kick-start” life at seafloor interfaces (http://www.jpl.nasa.gov/news/news.php?feature=4679). Barge and Burcar (from the RPI NAI team) also published a paper in Astrobiology about RNA oligomerization in iron sulfide chimneys (this was the product of a NAI Early Career collaboration grant from 2012). Barge and Russell published a Chemical Reviews review article of chemical gardens and “chemobrionics”, thus naming the emerging new field of harnessing self-assembling inorganic membranes as prebiotic chemistry catalysts (as in hydrothermal chimneys) but also for materials science applications. In the summer, Barge, Russell, Kanik, and student intern Lily Abedian published a paper about hydrothermal chimneys in the Journal of Visualized Experiments (JoVE) – the first video journal in chemistry. This resulted in a videographer from JoVE traveling to JPL to film us doing the experiment. The instructional video will be published online as part of the manuscript. This will greatly aid in dissemination of our research; and will show researchers in other labs how to correctly conduct “simulated hydrothermal chimney” experiments since it can be hard to explain in text.

This summer, Barge and Russell mentored four undergraduate student interns working on INV 2 projects. Lily Abedian (UC San Diego) tested the incorporation of phosphorus species into hydrothermal chimneys and sediments, finding that green rust (GR) in analog early Earth chimneys absorbs and concentrates P from the dilute ocean; this project will be continued in summer 2016 when Lily comes back to work with us. Erika Flores (Cal Poly Pomona) investigated the ability of green rust to absorb bio-relevant ions (sulfate and amino acids) in its interlayers, and measured the timescales of anion release. Erika’s work led to an ongoing collaboration with the microfluidics group at JPL and she is currently hired as a part-time laboratory assistant with the Icy Worlds team to continue this work. Arlette Valencia (Citrus College) focused on developing methods to analyze organics in green rust experiments, and along with our INV 2 Co-I’s at Oak Crest was able to analyze amino acids and ammonia. Timothy Lin (UC Riverside) and Ryan Cameron (Tulsa Community College) studied electrochemistry in hydrothermal chimney systems: the reduction of carbon dioxide using iron sulfides and green rust as catalysts. Timothy’s and Ryan’s work was successful and led to Ryan being hired as an Icy Worlds intern throughout the 2015-2016 year, and he successfully transferred from Tulsa Community College to Pasadena City College to pursue his electrical engineering degree in the LA area. Undergraduate interns at Oak Crest also worked on GR chemistry; they have developed rigorous methods of synthesizing GR anaerobically, and are investigating GR-driven nitrogen chemistry in hydrothermal systems. INV 2 had a large student cohort in summer 2015 and Barge and Co-I Baum (Oak Crest) held bi-weekly research meetings of INV 2-interested collaborators and all the student interns at Oak Crest.

This fall, INV 2 has one student intern (Ryan Cameron) and one laboratory assistant contractor (Erika Flores) who are focusing on rigorous investigation of electrochemistry and amino acid synthesis in prebiotic hydrothermal systems. Preliminary results – to be verified in coming months – indicate that iron-nickel sulfides are capable of acting as redox catalysts to reduce carbon dioxide from the early Earth ocean (to kick start an acetogenesis), and that green rust can react pyruvate and ammonia in prebiotic hydrothermal systems to synthesize amino acids (alanine).

In INV 3, Steve Vance, INV 3 Lead Investigator, is working with NAI Co-I J. Michael Brown (UW Seattle) to develop a revolutionary new way to compute thermodynamic properties of fluids under icy satellite pressure and temperatures. The computational framework for fitting thermodynamic data uses b-splines in combination with regularization techniques more typical in geophysics (Brown, in prep). Self-consistent Gibbs-energy based equations of state (EOS) from sound speed, density and heat capacity are yielding unprecedented precision and breadth in P and T needed for modeling conditions in ocean worlds. Brown has used the fitting framework to build an equation of state for liquid water to 100 GPa (100,000 atmospheres!) and 1000 K. Vance is applying the framework to an equation of state for pure ammonia, providing improved accuracy and instantaneous lookup to 4 GPa and 700 K (Vance and Brown, in prep). Postdoc Olivier Bollengier is working with Brown and Vance at the Mineral Physics lab at the University of Washington, obtaining the first calibrated measurements of fluid sound speeds in water and magnesium sulfate in a high pressure apparatus equipped for high precision (ppm) measurements of sound speeds. These efforts set the stage modeling aqueous chemistry in ocean worlds. To develop this work more rapidly, prepare for moving the experimental operations to JPL, and strengthen synergies with the NAI VPL team, Vance, Brown, and Co-I Rory Barnes (UW Seattle; VPL) are working with French scientist Baptiste Journaux to recruit him as a postdoctoral researcher working on EOS for liquids and their application to exoplanets.

In parallel with the EOS work, Collaborator Jun Kimura (ELSI, Tokyo) has demonstrated incorporation of the team’s present EOS for MgSO₄ to the evolution of Ganymede’s ocean through time. Vance is working with Christophe Sotin (Co-I JPL) on a revision of their model for satellite interiors (Vance et al. 2014) that can test the development of potentially habitable salty oceans above and below high pressure ices in Ganymede, other large icy moons, and also in watery exoplanets. Sotin is also working with JPL postdoc Klara Kalousova to examine the role of melt formation in high pressure ices, which constitute an icy analogue to rock-based volcanoes on Earth. In related work, Co-I Barnes is working with Vance to evaluate the likely abundance of watery super Earths, or “super Europas”, around other stars; they have identified up to 55 candidate worlds in the most recent Kepler space telescope data release; such worlds could have oceans with conditions analogous to those our team is simulating for Europa and Ganymede (Vance et al 2015a,b,c).

In shallower ocean settings with conditions more similar to Earth, Vance is considering global redox fluxes by analogy with Earth (Vance et al. 2015d). Among the five JPL summer students working with Vance in 2015, undergraduates Leila Chang (Yale, starting year 1) and Garrett Levine (Caltech, starting year 2) produced surprising new results that Vance and Co-I Pappalardo are using to assess the roles of seafloor hydrothermalism and exogenous materials, respectively, in Europa’s redox cycle. To assess the detailed transport of materials across Europa’s ocean, Vance is working with Co-I’s Jason Goodman and Bruce Bills to revise a model for Vance has assumed additional roles at JPL that leverage his role as a lead in the icy worlds project: Investigation Scientist for the Europa MASPEX instrument and Project Staff Scientist on the new Europa mission; and lead for a JPL internal investigation of science drivers for icy moon seismology. Co-I’ Bills and Jennifer Jackson (Caltech) are involved in that effort as well.

Vance and Co-I Mathieu Choukroun are co-authors on book chapters included in the in-press book, Low Temperature Materials (CRC Press).

In INV 4, We are conducting an experimental program designed to establish the extent to which chemical compositions of icy world surfaces are indicative of subsurface ocean chemistry/composition. Europa and other icy worlds containing vast global oceans beneath crusts of ice are key targets for understanding the impact of an extensive rock-water interface on a body’s habitability. This Investigation is shedding light on the evolution of ocean materials expressed on the surface of airless icy bodies and exposed to surface temperatures, vacuum, photolysis and radiolysis. Our work illuminates the connection between observables on the surface to the habitability of these past and present aqueous environments. This 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.

To date, comprehensive geochemical modeling efforts attempting to link putative ocean compositions with observed surface materials have been limited. Typical geochemical approaches do not account for out-of-equilibrium conditions encountered during rapid freezing at icy world surfaces. Even in the absence of radiative alteration, the details of how icy world ocean fluids would freeze out in the ice shell (and thus generate observable surface chemistry) are not well understood. This important aspect of the evolution of icy satellites is crucial to assess the nature of the chemical compounds that may reach the surface and act as tracers (possibly detectable from orbit or in situ) of chemical disequilibria at depth.

The work completed thus far examined what species form when NaCl and MgSO₄ brines are frozen to Europa surface temperatures using Raman spectroscopy. These results are summarized in a manuscript recently published by The Astrophysical Journal Letters.

The Icy Worlds Team at Jet Propulsion Laboratory is strongly committed to the principles of providing open access to research data produced using public funding; sharing such data for reuse, production of derivatives, or validation of research findings is fundamental to the soul of science and the advancement of astrobiological study. Progress in our compliance with data and sample management requirements outlined by the NASA Astrobiology Institute and described in the Icy Worlds research proposal are detailed in this report.

In the following sections, we summarize our short-term and long-term processes that have been designed and implemented to archive data from Icy Worlds research products and make it openly accessible in convenient, downloadable, and searchable indexed formats.

Following communication with each JPL Investigation Lead about data generation and workflow, as well as format and volume of data, the responsibility for transferring datasets to the archive is the responsibility of the Co-I. The wide variety of data volumes and formats supports this process. Fully reduced, validated, and corrected data products is produced under the direction of each Investigation Lead. The Co-I’s, with advisement from the data engineer (Ivria Doloboff of JPL Icy worlds Team) , are responsible for coordinating all Icy Worlds scientific investigations involving the use of calibrated data from their respective instruments and experiments, and ensuring that all science data products, including information required to interpret these products, are delivered to the archive within the two year window requirement. The datasets must include sufficient detail to permit examination for the purposes of replicating the research, responding to questions that may result from errata or misinterpretation, establishing authenticity of the records and confirming the validity of the conclusions; any model descriptions (where an .xlsx cannot preserve the data appropriately) will adhere to emerging high standards for sharing such information (see: http://www.geoscientific-model-development.net/submission/manuscript_types.html).

The current process in place for satisfying data archiving and accessibility requirements makes use of the existing agency-wide data management resource: data.NASA.gov and the supplementary materials section of journals in which data products are published. In the event that a journal is unable to include all data in the supplementary materials section, data.NASA.gov will be used to make datasets accessible. In order to utilize the Data.Nasa.gov resource, a JPL hosted-server hosted on conventional clustered NetApp filers with connectivity via NFS, CIFS, or iSCSI with RAID-6 protection archives the data in bulk. Using the Large Data Transfer Tool, users can transfer data to the contacts Jason Duley or Beth Beck at Data.NASA.gov who will immediately generate an XML metadata record for the uploaded dataset. The data generator must provide a title, description, point of contact name and email, issued and modified dates, keywords, spatial or temporal elements, and references including mission pages and publications. The XML and JSON formats provided by Data.NASA.gov satisfies the machine-readable requirement for data access and is the most up-to-date format for metadata generation and preservation; project tracking, indexing, re-use of datasets, and identification of version and collection are possible with careful metadata creation, preservation, and validation.

The long-term process envisioned by the Icy Worlds PI and data engineer is the deployment of an Icy Worlds Packaged Science Data System. Working in concert with the Center for Data Science and Technology in JPL’s Mission Systems and Operations Division, a data architecture will be constructed within the JPL Icy Worlds server to allow for front-end access of datasets by the public via a portal on the newly released Icy Worlds website. There will be a second portal for internal/restricted access to directly communicate and share with internal and external collaborators. The architecture of the packaged science data system would be divided by investigation, publication, and instrument. XML metadata records would continue to be generated and remain the standard format of datasets available within the archive. Curation of metadata will augment efforts for the long-term archive and preservation process by permitting query of data objects through attributes instead of physical names or locations (e.g. data object, resource, instrument, collection, user, method).