 SUBSURFACE WATER ICE MAPPING (SWIM) ON MARS: FOCUSED STUDY REGIONS. Z.M. Bain,​1            N.E. Putzig,​1 G.A. Morgan,​1 D.M.H. Baker,​2 A.M. Bramson,​3 S.W. Courville,​1 C.M. Dundas,​4 R.H. Hoover,​5 D.               Hornisher,​1 G.M. Nelson,​1 S. Nerozzi,​3 ​A. Pathare,​1 M.R. Perry,​1 E.I. Petersen,​2 H.G. Sizemore,​1 B.A. Campbell,​6 M.                Mastrogiuseppe,​7 M.T. Mellon,​8 ​I.B. Smith.​1 ​1​Planetary Science Institute, ​2​NASA Goddard Space Flight Center,             3​Lunar and Planetary Laboratory, University of Arizona, ​4​U.S. Geological Survey, ​5​Southwest Research Institute,             6​Smithsonian Institution, ​7​Sapienza University of Rome, ​8​Cornell University. Contact: zbain@psi.edu.   Introduction: ​The Subsurface Water Ice     Mapping (SWIM) project supports an effort by       NASA's Mars Exploration Program to determine in       situ resource availability [1-2]. We are performing       global reconnaissance mapping and focused     multi-dataset mapping to characterize the distribution      of water ice from 60ºS to 60ºN (Fig. 1). In 2019, we            produced ice consistency maps for the northern       hemisphere (0-60ºN and 0-225ºE, 290-360ºE). In      2020, we are extending our mapping into the        southern hemisphere (0-60ºS) and 225-290ºE in the       northern hemisphere at elevations < +1 km. Our maps         are being made available on the SWIM Project        website (​https://swim.psi.edu​), and we intend to      complete our global mapping by the summer of 2020.         Follow us on Twitter @RedPlanetSWIM for project       news and product release information. The SWIM Datasets: ​To search for and       assess the presence of shallow ice across our study         regions, we are integrating multiple datasets to       provide a holistic view of the upper 10s of m of the            Martian subsurface. The individual datasets and      methods we employ include neutron-detected     hydrogen maps (MONS), thermal behavior (TES,      THEMIS, and MCS), multiscale geomorphology     (HiRISE, CTX, HRSC, and MOLA), and radar       surface and subsurface echoes (SHARAD). Consistency Mapping: For the SWIM     2019 maps, we used the SWIM equation [2-3] to         provide a quantitative assessment of how consistent       (or inconsistent) the various remote sensing datasets       are with the presence of buried ice. The SWIM         Equation yields ice consistency values ranging      between +1 and -1, where +1 means that the data are           consistent with the presence of ice, 0 means that the          data give no indications of the presence or absence of          ice, and -1 means that the data are inconsistent with          the presence of ice. Here, we focus on our mapping          of features and ice consistency values in areas of         special interest to the SWIM project.  For more information on the project and its        techniques and datasets, visit our website and       associated presentations at this LPSC: Putzig et al.        (summary of results), Perry et al. (SWIM Equation        and methods), Sizemore et al. (thermal and neutron        analysis), Baker et al. (geomorphology), Morgan et       al. (radar surface reflectivity), and Petersen et al.        (radar subsurface mapping). Figure 1: ​Caption Composite map incorporating resulting from 2019 SWIM and highlighting the new regions               covered in 2020 SWIM. The 2019 study area in the northern hemisphere shows where data are consistent (blue) and                   inconsistent (red) with the presence of subsurface water ice. Our 2020 analysis focuses on areas below 1 km in                   elevation (rainbow color scale), as those elevations are considered accessible for human landing sites. https://swim.psi.edu/ Focused Study Regions: ​While large-scale     consistency mapping allows us to understand where       ice may be present regionally and globally, it is         important when selecting landing sites for future       human or robotic missions to have the best possible         understanding of the small-scale lateral and vertical       distribution of ice for particular locations of interest.        As such, we will choose a dozen or so smaller (~100           km or less) sites in which to carry out highly focused           intensive analyses, which would be impractical to       apply on a global scale. For these sites, we will also           consider methods of integrating the various data sets        other than the SWIM Equation used previously. If        such alternatives are not applied globally, a Bayesian        approach described by Perry et al. [4] may be used. Study Sites​: Our list of sites to be analyzed         has not been finalized, but we have selected several.         To test our overall methods, we will scrutinize results         at both the Phoenix landing site (outside of our         nominal study area) and locations of ice exposing        impacts [5]. These locations provide essential ground       truth for ice on Mars. In particular, the Phoenix         landing site (68.22°N, 234.3°E) is the only location        where there have been direct measurements of the        presence and depth to the top of the ice, which allows           us to validate our techniques in a way that we cannot           elsewhere on the planet. We will also study a number          of previously proposed human landing sites,      including two that fall outside of our nominal study         region (i.e., they are at elevations > +1 km): Southern          Nectaris Fossae (28.88°S, 300.29°E) and Western      Noachis Terra chloride deposits (37.33°S,     350.648°E) [6,7].  Methods of intensive analysis​: ​For the sites       of intensive analysis, we will begin by applying all         the methods used for the larger SWIM study, and         then we will apply a number of new techniques at a           finer scale for these sites.  Subsurface Radar​: The techniques of the      subsurface radar team will be the same as outlined in          Petersen et al. [8], but more effort will be made to           make as many estimates of the dielectric properties        where reflectors are present to improve lateral       resolution in dielectric properties. Geomorphology: ​We will use available     HiRISE images to evaluate small-scale landforms      that are not visible in CTX images and/or at the          scales assessed in the global mapping effort. These        include meters-scale polygons, which have a variety       of origins but may indicate near-surface ice [9].        Higher-resolution analysis of CTX images will also       provide context for the landforms identified in       HiRISE and help tie the results to the global maps. Combined Radar Thermal Model: ​We will      leverage the overlapping, but distinct probing depths       of the thermal datasets (<1 m) relative to the         SHARAD surface returns (5 m) to permit       two-layered modeling of the composition of the       upper 5 m. As ice is a low density, high thermal           inertia material, directly comparing radar reflectivity      with thermal data provides an avenue to exclude false         positive signals associated with each dataset (i.e.,       rock and ice are thermally indistinguishable, whereas,       for radar, porous sediments and ice may appear        nearly identical to one another).  Thermal Analysis: During the 2019 SWIM      project, in parallel with a global TES analysis [10],         we examined nighttime THEMIS data at 49 locations        in the northern hemisphere [11], applying the       methods of Putzig et al. [12] to search for evidence of           ice. Although this technique had proven effective for        ice detection on the polar erg, spatial and temporal         coverage limited its efficacy at lower latitudes. We        subsequently carried out a pilot study for a new         technique of bundling THEMIS data from      morphologically similar LDAs in Deuteronilus to      achieve improved seasonal coverage and     ice-detection capabilities. Preliminary results are     promising, and this new technique will be applied to         a subset of our sites of interest in our 2020 study.  References: [1] Morgan G. A. et al., Mapping        Water Ice on Mars: Human Mission Resources and        Climatic Implications, submitted to ​Nature     Astronomy​. [2] Putzig N.E. et al. (2019) ​Ninth Int.         Conf. Mars​, no. 6427. [3] Perry M.R. et al. (2019)          LPSC ​50, 3083. [4] Perry M.R. et al. (sub.) ​LPSC 51.           [5] Dundas C.M. et al. (2014) ​J. Geophys. Res., 119,          109-127. [6] Boatwright B. D. LS/EZ Workshop for        Human Missions to the Surface of Mars, 1005 [7]         Hill J. R. and Christensen P. R. LS/EZ Workshop for          Human Missions to the Surface of Mars, 1021 [8]         Petersen E.I. (sub.) ​LPSC 51. [9] Levy J. et al. (2009)           J. Geophys. Res. 114, E01007. [10] Sizemore H.G. et         al. (sub.) ​LPSC 51. [11] Hoover R.H. et al. (2019)          LPSC 50, 1679. [12] Putzig N.E. et al. (2014), ​Icarus          230, 64-76. 
