Ice-dust mantles on Mars David Hollibaugh Baker NASA Goddard Space Flight Center SWIM Team Telecon 25 October 2018 Glacial deposits, plains, and mantle units mapped from CTX image mosaic at 1:50,000 scale Study Area: Deuteronilus Mensae SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 2 Three units mapped in study area Plains Mantle Glacial Deposits SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 3 Morphologic evidence of ~100 m thick mantle unit onlapping glacial deposits Mantle Mantle Glacial Deposit Glacial Deposit Mantle Plains HRSC DTM data Baker and Head (2015) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 4 Relatively smooth with: Rimless craters. Small pockmarks or depressions. Fractures <20 m in width; some forming circular patterns. SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 5 Upl LDA CTX image P13_006160_2252 SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 6 Morphologic evidence of ~100 m thick mantle unit onlapping glacial deposits Mangold (2003) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 7 Mantle shows collapse features and fractures, possibly related to sublimation of buried ice Mantle Mantle Glacial Deposits SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 8 Middle Amazonian (~500 Ma) age SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 9 Analyzed SHARAD Radargrams Plains Mantle Glacial Deposits SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 10 279 SHARAD tracks analyzed over mantle SHARAD tracks analyzed SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 11 101 SHARAD tracks showed reflectors SHARAD tracks with reflectors SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 12 101 SHARAD tracks showed reflectors Thick and continuous: Thin and Many reflectors patchy: Few reflectors SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 13 Thick occurrences of mantle unit Glacial Deposits Surrounded by glacial deposits Isolated Patch Plains SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 14 Tw o -way time delays show deep and shallow reflectors shallow deep SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 15 Histogram of two-way time delays 800 shallow 700 600 500 400 deep 300 Frequency 200 100 0 0 0.75 1.75 2.75 3.75 4.75 5.75 6.75 7.75 8.75 9.75 Two-Way Time Delay (µs) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 16 Shallow reflectors in mantle surrounded by plains SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 17 Reflector traces compared with clutter simulations to confirm source radargram 1μs unit boundaries (PDS, US) traced 1μs surface radargram clutter reflection subsurface reflector clutter simulation (UT) Choudhary et al. (2016) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 18 Upper plains mantle likely desiccated from original ice content. Consistent with mAl of Skinner et al. (2012) LDA Mantle on ε ~ 5 LDA Mantle SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 19 Middle Amazonian Lowland Unit (mAl) (Skinner et al., 2012) LPSC 48, 21 March 2017 - Baker and Carter, Mars Radar Reflectors - 20 Skinner et al. (2012): “Our observations are consistent with the widespread emplacement of a loess-like deposit tens of meters thick in the Martian northern lowlands during the Middle Amazonian due to climate-driven erosion of the north polar plateau” SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 21 Pedestal Craters (Kadish et al., 2009) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 22 Utopia Planitia – Scalloped Terrain SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 23 Utopia Planitia Utopia Planitia Deuteronilus Mensae Deuteronilus Mensae Utopia Planitia Continuous Mantle Thickness of several tens of meters. Highly polygonalized. Latitude-dependent degradation dominated by sublimation and differences in insolation. Lower Plains SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 24 Mantle in Arcadia (Ramsdale et al., 2018) pitted smooth SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 25 Arcadia Expanded Secondaries (Viola et al., 2015) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 26 Hellas Region (LeFort et al., 2010) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 27 Southern Mid-Latitude Scarps (Dundas et al., 2018) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 28 Latitude Dependent Mantle e.g., Mustard et al., 2001; Miliken et al., 2003; Head et al., 2003; Kostama et al., 2006; Schon et al., 2009 Mean crater retention age of 0.1 Ma (Kostama et al., 2006); older at southern latitudes. Thickness of several meters to tens of meters. Desiccation via sublimation at mid- latitude regions during low obliquity excursions. LPSC 48, 21 March 2017 - Baker and Carter, Mars Radar Reflectors - 29 Dickson et al. (2015) SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 30 SWIM Telecon, 10/25/2018 - Hollibaugh Baker, Mars Mantle - 31.