Modeling the Volatile Speciation of High Temperature Fluids on Europa Christine Ray (1,2), Christopher Glein (2), Kelly Miller (2) and J. Hunter Waite (2,1) (1) Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, TX 78249 (2) Space Science and Engineering Division, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 (christine.ray@swri.org) Introduction Volatiles produced in high temperature fluids by outgassing of accreted chondritic material during Eu- ropa’s formation, or by magmatic/hydrothermal activ- ity in Europa’s present-day silicate interior, may be a key source of chemical energy in Europa’s ocean ([4] and [6]). Transport to the ocean of reduced volatiles produced by such processes could couple with the de- livery of surface oxidants to create chemical disequi- libria, which may provide energy for life. Of key im- portance are the volatiles H 2 , CH 4 , CO 2 ,N 2 , and NH 3 which can be detected by the MASPEX instrument [1], and the anions HCO − 3 , CO −2 3 , and NH + 4 which can be detected by the SUDA instrument [3], on Europa Clip- per. The fluxes of these volatiles into the ocean, which depend on the geochemical properties of high temper- ature fluids and the amount of heat transferred from the silicate interior, need to be estimated to assess the hab- itability of the ocean. Here, we explore how the pH, oxidation state, temperature, pressure, and total car- bon/nitrogen budgets of Europa’s interior govern the input of volatiles to the ocean. Methodology We calculate the speciation of carbon and nitrogen volatiles in Europa’s magmatically derived fluids from the molal ratios of volatiles consistent with chemical equilibrium. Using geochemical analogs of hydrother- mal systems on Earth [7] and Enceladus’ ocean [2], we consider a plausible range of values for tempera- ture, pH, oxidation state (which we represent by hy- drogen activity, a H2 ), and total carbon/nitrogen bud- gets in Europa’s interior. We convert the ideal molal ratios of each species into concentrations using mass balance relationships for carbon and nitrogen. In de- termining values for the concentrations of total carbon and nitrogen, we consider analogs of Earth, carbona- ceous chondrites, and comets. To characterize the ef- fect of each individual geochemical parameter on fluid composition, nominal reference values are utilized for all but the parameter of interest in each calculation. Results & Discussion We present the volatile speciation of high- temperature fluids on Europa for different combina- tions of pH, H 2 activity, temperature, pressure, and total carbon/nitrogen concentrations. An example is shown in Figures 1 and 2, where we have fixed the pressure at the Europa seafloor pressure (1500 bar) and the oxidation state (aH 2 ) at the fayalite-magnetite- quartz (FMQ) buffer: 1.5 Fe 2 SiO 4    fayalite +H 2 O → Fe 3 O 4    magnetite +1.5 SiO 2    quartz +H 2 . (1) Under these conditions, we find that temperature has the strongest control over speciation of carbon and ni- trogen volatiles at high temperatures, while pH has the strongest control over the speciation at lower temper- atures. At temperatures greater than ∼ 500 ◦ C, the most oxidized volatiles (CO 2 and N 2 ) dominate over reduced volatiles if equilibrium can be reached. At the low to mid temperature range (200-500 ◦ C), reduced species (CH 4 , NH 3 or NH + 4 ) are more abundant, but the relative abundances of these volatiles depend on pH. We consider how each of the parameters in our model would affect the concentration of volatiles into the ocean, and the composition of Europa’s hydrother- mal fluid. Finally, we discuss the impact that each of our considered variables could have on the amount of chemical energy available in the ocean, and the po- tential for these variables to be constrained by future observations from Europa Clipper. EPSC Abstracts Vol. 13, EPSC-DPS2019-1171-2, 2019 EPSC-DPS Joint Meeting 2019 c  Author(s) 2019. CC Attribution 4.0 license.