Is Europa Active and Suitable for Life? - How Europa Clipper and its Habitability Assessment Board (HAB) are working to synthesize observations to characterize Europa and its potential activity.

<p><strong>Introduction:</strong> The habitability of Europa is a property within a system, with many interdependent physical and chemical parameters, among a number of processes, of which no single measurement or investigation can characterize. Therefore, investigating Europa as an integrated system must occur to understand the complete picture. To accomplish this, the Europa Clipper mission has three main mission objectives to assess Europa’s habitability: (1) characterize the Ice Shell and Ocean: including their heterogeneity, properties, and the nature of surface–ice–ocean exchange; (2) characterize the Composition: understanding Europa’s ocean through investigations of the composition and chemistry; (3) and characterize the Geology: including surface features and high-science-interest localities. Europa Clipper will also assess any current or recent activity by searching for evidence of thermal anomalies and plumes and will perform high resolution observations to provide reconnaissance for a future potential landed mission. Synthesizing the mission’s science measurements in such a way as to constrain Europa’s habitability is a complex task and is being guided by the Habitability Assessment Board (HAB).</p><p>The HAB is charged with providing a high-level, cross-instrument and cross-discipline, habitability-driven science perspective. All members of the Europa Clipper Science Team are considered members of the HAB and so contribute to addressing the overarching goal of the mission. Rotating members of the science team serve as leadership of the HAB and convene regular meetings to discuss and formulate recommendations to the project’s science leadership. Particularly, HAB works to connect activities and measurements across the Europa Clipper Geology, Composition, and Interior Working Groups to investigate habitability and can recommend formation of focus groups of experts on the team to address scientific and technical problems related to habitability.</p><p><strong>System Science:</strong> To achieve mission level 1 requirements and assess Europa’s habitability, investigations will contribute observations towards science themes. Themes that support the Ice Shell and Ocean characterization include Full Depth Subsurface Exchange, Shallow Subsurface Structure, Ice Shell Properties, and Ocean Properties. For Composition characterization, themes that contribute include Global Composition Surface Mapping, Regional Composition, Atmospheric Composition, and Space Environment Composition. The Geology objective has contributions of Global Surface Mapping, Landform Geology, and Local Scale Surface Properties (which also contributes to reconnaissance). Current activity is supported by Remote Plume Search (and Characterization, if applicable), In-Situ Plume Search (and Characterization, if applicable), Surface Thermal Anomaly Search, and Surface Activity Evidence.</p><p><strong>Current Activity:</strong> Searches for and characterization of any recent activity would greatly contribute to assessing Europa’s habitability. Europa Clipper plans observations for potential activity through remote observations including: the Europa-Ultraviolet Spectrograph (Europa-UVS) instrument through occultations, aurora, and UV scans; the Europa Imaging System (EIS) Narrow Angle Camera (NAC) through high resolution imaging; and the Europa Thermal Imaging System (E-THEMIS) through thermal infrared mapping. Additionally, in-situ measurements by the SUrface Dust Analyzer (SUDA) will also make observations of activity through detections of positive and negative ions and characterization of particle compositions and their locations of origin on the surface. Contributions by the other instruments will also inform on current/recent activity through remote and in-situ observations through magnetic, plasma, radar, and compositional measurements.</p><p>Remote observations to search for (and characterize if present) current activity at Europa by ground based, near-earth orbiting observatories, and other spacecraft could also occur, even while Europa Clipper is in transit to Jupiter. Recent observations by the Hubble Space Telescope (HST) have made putative detections of plume activity at Europa (Roth et al., 2014; Sparks et al., 2016) and future observations by the James Webb Space Telescope (JWST) and ground-based observatories may be able to confirm these findings. JWST can make measurements in the mid-infrared, for which the Galilean moons are relatively poorly characterized, enabling further constraints on composition and mechanisms driving the activity. Other observatories including the Very Large Telescope (VLT), the Atacama Large Millimeter/submillimeter Array (ALMA), and measurements by the Juno spacecraft and future JUICE mission could all contribute further to assessing Europa’s potential activity and habitability. The Europa Clipper science team is currently working to informally coordinate efforts with the JUICE team to enhance our science as possible at Europa on a non-interference basis.</p><p><strong>Summary:</strong> Europa Clipper will assess the habitability of Europa as a system, guided by the HAB, through the synergy of multiple measurements and incorporation of remote observations by JWST and other remote observatories and spacecraft. Potential detections (and subsequent characterization) of any activity would greatly contribute to understanding Europa’s habitability and potential to harbor life. Discovery awaits!</p><p><strong>References:</strong></p><p>Roth et al. (2014), Transient water vapor at Europa’s south pole. <em>Science</em>, <em>343</em>(6167), 171-174.</p><p>Sparks et al. (2016), Probing for evidence of plumes on Europa with HST/STIS. <em>The Astrophysical Journal</em>, <em>829</em>(2), 121.</p><p><strong>Acknowledgments</strong>: This work was supported by NASA through the Europa Clipper Project. Portions of this work were performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. </p>