Final Grant Report 2018: Virtual Planetary Laboratory at The University of Washington Reporting Period: January 1, 2013 – December 31, 2018 PI: Victoria Meadows (UW) Contents Overview ................................................................................................................................................. 2 Our Research: Year 1 ............................................................................................................................. 3 Our Research: Year 2 ............................................................................................................................. 8 Our Research: Year 3 ........................................................................................................................... 16 Our Research: Year 4 ........................................................................................................................... 25 Our Research: Year 5 ........................................................................................................................... 35 Our Research: Year 6 (NCE) ............................................................................................................... 49 New Technology ................................................................................................................................... 56 Publications (398 Total) ........................................................................................................................ 57 NAI Information Management System 1 of 91 Overview The Virtual Planetary Laboratory’s interdisciplinary research effort focuses on answering a single key question in astrobiology: If we were to find a terrestrial planet orbiting a distant star, how would we go about recognizing signs of habitability and life on that planet? This question is relevant to the search for life beyond our Solar System, as outlined in NASA's Astrobiology Strategy. VPL research addresses many of the Strategy Key Research Areas and questions including How can we enhance the utility of biosignatures to search for life in the Solar System and beyond (Section 5.4 Research Area II) and How can we identify habitable planets and search for life beyond the Solar System? (Section 5.4 Research Area IV). Recent observations have brought us much closer to identifying extrasolar environments that could support life. The successful Kepler Mission has discovered most of the now over 3,500 known extrasolar planets – many of them smaller than twice the diameter of the Earth – and several residing in the habitable zones of their parent stars. Ground-based telescopes and the K2 mission are now finding potentially habitable planets around nearby M dwarfs, including a potentially Earth-mass planet in the habitable zone of Proxima Centauri, the Sun’s nearest neighbor, and the seven Earth- sized planet TRAPPIST-1 system, where three of these planets are likely in the habitable zone. These targets and others found by the Transiting Exoplanet Survey Satellite (TESS) mission – slated for launch in 2018 – will provide potentially habitable targets for the planned James Webb Space Telescope (JWST), which could probe the atmospheric composition of at least one habitable zone terrestrial planet. In the longer term, we anticipate large spaceborne telescopes, such as NASA’s LUVOIR or HabEx concepts, that can directly image and obtain spectroscopy of a larger sample of potentially habitable terrestrial extrasolar planets. The VPL provides a scientific foundation for interpreting data from extrasolar terrestrial planet detection and characterization missions such as Kepler, K2, TESS, JWST and LUVOIR/HabEx. To provide this foundation, the VPL uses data from NASA's Earth observing and planetary exploration programs, and information from field and laboratory studies and Earth's geological history, to validate and develop more comprehensive models of terrestrial planets. These models allow us to simulate and explore the likely diversity of extrasolar planet environments in advance of the more challenging spacecraft observations. VPL's models can be used to understand the radiative and gravitational effects of stars on the planets that orbit them. Combinations of model, lab, and field work are also used to understand which biologically-produced gases can generate a detectable biosignature in globally-averaged planetary observations. Finally, models and instrument simulators tell us how best to extract planetary environmental parameters from astronomical observations that have no direct spatial resolution, and that may also be limited in sensitivity, spectral resolution and temporal sampling. The team required to develop and run these models is necessarily large, and highly interdisciplinary. Our research encompasses single-discipline efforts that produce results pertinent to our overarching habitability and biosignatures focus, to highly interdisciplinary efforts where stellar astrophysicists, NAI Information Management System 2 of 91 planetary climate modelers, orbital dynamicists, atmospheric chemists and biologists work together to determine the effects of stellar radiation and gravitation on the habitability of terrestrial planets. Our research can be divided into five main tasks: Solar System Analogs for Exoplanets, Early Earth, The Habitable Planet, The Living Planet and The Observer. The first four tasks explore known and simulated environments to understand the factors that affect habitability and the global impact of life on its environment, and to expand the plausible range of terrestrial planet environments – both inhabited and uninhabited. This knowledge can be used to help prioritize newly discovered potentially habitable planets for more-detailed observational follow-up, and to generate new biosignatures to be sought in planetary spectra. The fifth task uses the models and data generated and gathered in the first four tasks to assess the remote detectability of newly identified potential global signs of habitability and life. Our Research: Year 1 Earth as an Extrasolar Planet. In this task we use observations of our home planet to explore the detectability of signs of habitability and life on terrestrial planets. In collaboration with LCROSS mission scientists, this year Robinson, Meadows and Sparks performed a comparison of predictions from the VPL 3-D spectral Earth model with UV to infrared spectra of the Earth obtained by the LCROSS mission (Robinson et al., submitted). This comparison was used to validate our predictions of the detectability and spectral dependence of glint from the Earth’s ocean, and it also revealed an error in the spectral calibration of data from the LCROSS mission, which we were able to help correct. We also discuss using the UV Hartley band of ozone as a biosignature. This year we also added N2-N2 collisionally-induced absorption (CIA) to the VPL Earth model. The updated model has been used to demonstrate that N2- N2 CIA is required to fit the spectral region near 4.1um in Earth spectra taken by the NASA/EPOXI mission (Schwieterman et al., in prep). Detection of N2-N2 CIA in a planet’s spectrum can help constrain surface pressure and, thus, surface habitability. We also completed spectral libraries of the Earth’s appearance through a Lunar month as a simulated dataset for studies of observations of the Earth from a lunar platform. Early Earth and Mars: In this task we work to understand the early Earth and Mars environments, both of which serve as potential analogs for habitable environments unlike those seen on Earth today. In our early Mars studies on surface environments, David Catling and collaborators completed work on understanding the origin and abundance of carbonates on Mars (Niles et al., 2013), and the environmental implications of clay minerals (Ehlmann et al., 2013). Photochemical modeling of the formation of salts from the oxidation of gases in the atmosphere of early Mars was also performed (Smith et al., 2013). Ongoing efforts include work on the possibility of oceans on Mars and the formation of salts in the soil. Conrad participated extensively in work using instrumentation on the Curiosity Rover to NAI Information Management System 3 of 91 assess the current and past habitability potential for Mars (e.g. Mahaffey et al., 2013; Leshin et al., 2013). Kasting, Ramirez, Kopparapu, Robinson, Freedman and Zugger collaborated on studies of the warming of Early Mars by using CO2 and H2 (Ramirez et al., 2013). They modeled the origin, abundance and lifetime of CO2 in the early Martian environment, and investigated the possible abundance of H2 on early Mars, since H2 can act as a secondary greenhouse gas via collision-induced absorption. For studies of the early Earth’s environment, we made progress in the areas of Earth’s geochemical history and its implications for life, climate evolution, and the evolution of atmospheric oxygen levels. Studying the Earth’s geochemistry, Buick and colleagues discovered a soluble and reactive phosphorus species (phosphite) in early Archean carbonates (Pasek et al., 2013) that was likely of meteoritic origin. Phosphite’s delivery during the Late Heavy Bombardment may have driven chemistry to form cell membranes and make nucleotides, a precursor to the RNA World hypothesis for the origin of life. Team members also explore the effectiveness of H2 as a greenhouse gas on the early Earth (Wordsworth and Pierrehumbert, 2013) with commentary on the paper from team member Kasting (Kasting 2013c). In understanding the history