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Executive Summary

Our goal in the Astrobiology of the Icy Worlds Investigation is to advance our understanding of the role of ice in the broad context of astrobiology through a combined laboratory, numerical, analytical, and field investigations. Icy Worlds team will pursue this goal through four major investigations namely, the habitability, survivability, and detectability of life of icy worlds coupled with “*Path to Flight*” Technology demonstrations.

A search for life linked to the search for water should naturally “follow the ice”. Can life emerge and thrive in a cold, lightless world beneath hundreds of kilometers of ice? And if so, do the icy shells hold clues to life in the subsurface? These questions are the primary motivation of our science investigations which are as follows:

*Habitability of Icy Worlds investigates the habitability of liquid water environments in icy worlds, with a focus on what processes may give rise to life, what processes may sustain life, and what processes may deliver that life to the surface.

*Survivability of Icy Worlds investigates the survivability of biological compounds under simulated icy world surface conditions, and compares the degradation products to abiotically synthesized compounds resulting from the radiation chemistry on icy worlds.

*Detectability of Icy Worlds investigates the detectability of life and biological materials on the surface of icy worlds, with a focus on spectroscopic techniques, and on spectral bands that are not in some way connected to photosynthesis.

*Our technology investigation, a Path to Flight for astrobiology, utilizes instrumentation built with non-NAI funding to carry out the science investigations discussed above. The search for life requires instruments and techniques that can detect bio-signatures from orbit and in-situ under harsh conditions. Advancing this capacity is the focus of our Technology Investigation.

The following sections highlight some of our accomplishments for the above investigations.

In this reporting period, we continued to work on Habitability of Icy Worlds. We investigated conditions relevant to sea floor processes that might be conducive to originating and supporting life in icy world interiors. We continued to test the hypothesis that life can originate through a seafloor process that occurs at temperatures lower than those occurring in hydrothermal systems at mid-ocean ridges.

One of the tasks in this investigation was to obtain equations of state (thermodynamic properties) for aqueous ammonia under deep ocean pressures and temperatures, incorporate new data and existing MgSO₄ data into thermodynamic databases and investigate additional solutions. We developed Pitzer thermodynamic parameters for aqueous magnesium sulfate (Phutela and Pitzer 1986) that allow the team to express their thermodynamic equation of state for MgSO₄ (Vance and Brown 2013) in terms of the new Gibbs energy framework and in a way that is referenced to formulations for other aqueous systems. This innovation clears the path to both computing melting and freezing phase equilibria and salt precipitation for the MgSO₄ system.

Bacterial spores are one of the toughest and most durable forms of life on earth. Can bacterial spores, embedded in near surface Europan ice, survive the Jovian radiation environment? Can either the spores or their organic radiolysis products be detected spectroscopically through remote sensing? As a part of Icy Worlds Survivability investigation, Icy world Team investigators focused on those questions and published their results concerning the spectral properties of bacterial spores in cryogenic ices as well as their viability under solar radiation. Briefly, they found that B. subtilis spores generate low molecular weight photoproducts when irradiated with UV at low temperature and pressures (100K and 10^-9 Torr).

As far as the Detectability of Icy Worlds investigation is concerned, we investigated the surface chemistry of Mars, an icy body. Dalton and co-workers reported Visible and near-infrared wavelength (VNIR, lambda = 0.35-5 mu m) laboratory diffuse reflectance spectra and corresponding optical functions (real and imaginary refractive indices) for several iron sulfades. Another study relevant to the Detectability of Icy Worlds investigation was conducted by involvement of investigators from the Icy Worlds team regarding weathering effect of surfaces Jovian and Saturnian satellites which are important for understanding chemistry of surface materials under weathering.

As far as the Field Instrumentation and Path to Flight investigation’s is concerned, Co-I Vance worked closely with a team at JPL to develop a new concept for probing the subsurface of Europa’s ice shell using Jupiter’s decametric emission (Romero-Wolf et al. 2014). As a part of Path to Flight, we continued to make great progress in “LIFE” mission concept (see Tsou et al., 2012; McKay, 2014) investigation for Enceladus, a low-cost sample return mission to a body with high astrobiological potential. We also presented the case that the plume of Enceladus currently represents the best astrobiology target in the Solar System.

References:

McKay, C. P., A. D. Anbar C. Porco,3 and P. Tsou, Follow the Plume: The Habitability of Enceladus, ASTROBIOLOGY Volume 14, Number 4, 2014.
Phutela, R. C. and Pitzer, K. S. (1986). Heat capacity and other thermodynamic properties of aqueous magnesium sulfate to 473 K. Journal of Physical Chemistry, 90:895–901.
Romero-Wolf, A., Vance, S., Maiwald, F., Heggy, E., Ries, P., and Liewer, K. (2014). A passive probe for subsurface oceans and liquid water in jupiter’s icy moons. Icarus, (to appear).
Tsou, P., Brownlee, D. E., McKay, C. P.; et al., LIFE: Life Investigation For Enceladus A Sample Return Mission Concept in Search for Evidence of Life , (2012) ASTROBIOLOGY, 12, Issue: 8 Pages: 730-742 DOI10.1089/ast.2011.0813
Vance, S. and Brown, J. (2013). Thermodynamic properties of aqueous MgSO4 to 800 MPa at temperatures from -20 to 100 oC and concentrations to 2.5 mol kg−1 from sound speeds, with applications to icy world oceans. Geochimica et Cosmochimica Acta, 110:176–189.
Vance, S., Bouffard, M., Choukroun, M., and Sotin, C. (2014). Ganymede’s internal structure including thermodynamics of magnesium sulfate oceans in contact with ice. Planetary And Space Science, 96:62–70.