Mars: Current State of Knowledge and Outstanding Questions Jack Mustard, Brown University Presentation to the Mars 3 2 3 Mariner 4, 6, 7 4 5 McKay, D. S.; et al. (1996). "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001". Science 273 (5277): 924–930. 6 What Were the Big Questions a Decade Ago? I. What are the major reservoirs of water? II. Does liquid water exist on/near the surface or at depth? III. What are the processes and history of climate? IV.What is the composition of the major geologic units (elemental/mineralogic)? V. What was the evolution of the surface and interior? What is the internal structure? 7 VI.Did/does Life exist? 1996 1999 2001 2003 2005 2007 2009 MarsMars MROMRO ExpressExpress Mars Global Surveyor MarsMars OdysseyOdyssey Mars Climate Orbiter MERMER PhoenixPhoenix Mars Polar Mars Lander8 Pathfinder What Were the Major Scientific Results for the Decade? 9 Last Decade Discoveries: Diverse Planet with Complex History •We have made significant advances in understanding the processes and history of climate, as well as understanding the evolution of the surface. • Mars has areas with diverse mineralogy, including alteration by water, with a change in mineralogy over time [MGS, ODY, MER, MEX, MRO] • In situ confirmation of Wet (Warm?) Climate in the past [MER] • Pervasive water ice in globally distributed, near‐surface reservoirs [ODY, MRO, MEX, PHX] • Sources, phase changes, and transport of volatiles (H2O, CO2) are known & some are quantified [MGS, MEX, MRO, PHX] • Increasing evidence for geologically recent climate change: stratified layers in ice and in rock [MGS, ODY, MEX, MRO] • Dynamic change occurring even today: landslides, new gullies, new impact craters, changing CO ice cover [MGS, ODY, MEX, MRO] 2 • Presence of methane indicative of active chemical processes either biogenic or abiotic [MEX and ground ‐based] •Based on much of the above, the perception of Potential for past Life has increased, and Modern Life may still be possible. Last Decade Discoveries: Diversity of Environments Chemistry and morphology indicate PHX changing environments throughout geologic history • Acidic waters at Meridiani • Basic waters at Phoenix landing site • Mineralogy: clays to sulfates to oxides MER Steno Smith Clays in Mawrth Valles Lyell Gilbert area MRO MEx Victoria Crater -11 Hesperian subsurface water, diagenesis Past Decade Results: Wide variety of sedimentary deposits Delta, showing phyllosilicate layers Melas Chasma MRO MRO/MEx MER Meridiani Large-scale sedimentary structures Depositional processes created a sedimentary record Eberswalde Delta • Developed in topographically low areas • Spectacular stratification at multiple scales • Evidence of persistent standing water, lakes • Sediments systematically change in character with time Fine-scale sedimentary structures • Multiple facies recognized -12 JezeroVolcan Crateric delta deposits ClosedOlivine-rich basin with defined inlets and an outlet Carbonate/clay MineralogyClay of the catchment basin includes abundant Fe/Mg smectite In the delta deposit and crater floor are indications of carbonate 75°E 80°E A phyllosilicate B -2900 700 0.01 0.05 elevation (m) 2.3 µm depth ae s os F i il N C Isidis Basin Syrtis Major northern delta western delta Fassett and Head (2005) 13 Ehlmann et al. (2008) Past Decade Results: Distribution of Modern Water Global Near-Surface ODY Reservoirs of Water Gamma Ray Spectrometer • Global hydrogen abundance and equivalent H2 O • Ground ice to +/-60° in high abundance Phoenix results PHX SHARAD and MARSIS MRO MEX • Nearly pure water ice • Distinct layering • No deflection of crust • Ice-cored lobate debris -14 aprons in mid-latitudes Past Decade Results: Ancient Mars Was Wet (Episodically?) Channels formed by rainfall runoff Delta, deposition into standing water MRO MRO Eberswalde Delta Ancient features indicate water present at the surface • Evidence of persistent standing water, lakes • Evidence of rainfall, valley networks • Lake overflow features Mojave crater -15 Past Decade Results: Evidence for Water/Rock Interaction MRO MEX hydrated MRO silica/altered 75 m k glass roc ed zeolite (analcime) r lte chlorite and A smectite k roc h es Fr Southern Highlands Widespread alteration, Impact generated hydrothermal alteration MER Gertrude Weise image -16 Hydrothermal deposits Columbia Hills Jack Farmer Past Decade Results: Mars Still Active Today MEX Mid-latitude mantles MGS, MRO and gullies Noachis Terra MGS ODY Hecates Tholus Lava Flows MGS Albor Tholus New Volcanic activity spans most or Impact all of martian geologic history Craters MRO -17 Past Decade Results: Atmosphere and Climate Results Dust storm Dust storm Dust storm Climate change -- Past, season season season recent and past: Understanding the process • Early wet (warm?) Mars (Noachian) has evolved to cold, dry Mars (Hesperian +) • Periodic change in last several million years Recent multi-year record of CO2/water/dust; atmospheric MGS, MRO dynamics [MGS, ODY, MEX, MRO] Understand how the atmosphere works • Seasonal cycles and interannual variability SO , Argon, CH4, CO, etc.: PHX 2 Tracers of transport, PHX chemistry, and surface- atmosphere interactions North Pole Cloud, fog and storm dynamics MEX, MRO -18 Past Decade Results: Periodic Climate Change • Latitude dependent mantle Modeled Ice Table Depth [m] Volatile-rich, latitude dependent deposits (mantle, glaciers, gullies, viscous flow) coupled to orbitally-forced climate change Periodicity of layering in the north polar cap deposits as well as sedimentary deposits MGS, ODY, MEX MRO Past Decade Results: Modern Methane courtesy Mark Allen NAI, R&A Courtesy Mike Mumma Detection of Methane on Mars NAI MEX NAI R&A Abiotic? Evidence of an Biotic? active subsurface? courtesy Lisa Pratt Past Decade Results: Mars Planetary Evolution Neutral pH acidic • Hydrous Mineralogy Changed Over Time Clays Sulfates Anhydrous Ferric Oxides MEx • Phyllosilicate minerals (smectite clay, chlorite, kaolinite…) formed early • Evaporates dominated by sulfate formed later with opal/hydrated silica • Few hydrated mineral deposits since • Evolution of Aqueous, Fluvial and Glacial, Morphology with Time • Valley networks, lake systems • Gullies • Viscous flow, glaciers, latitude dependant All Missions mantle <<1% of GLOBAL GEOLOGIC TIMELINE rock record 4.0 3.0 2.0 1.0 epoch boundaries from Hartmann and Neukum, 2001 ~50% of rock record Gyr 22 Diverse Hydrous Mineral Deposits Recognized from Orbital Data: Murchie et al., 2009 Noachian layered Noachian Meridiani- clays (type: Mawrth type layered Vallis) deposits (type: Terra Meridiani) Deep Noachian Hesperian Valles- phyllosilicates type layered exposed in highland deposits (type: craters, chasma walls Candor Chasma) (type: Tyrrhena Terra) Noachian intra-crater Amazonian gypsum fans with deposits phyllosilicate-rich (type: Olympia layers (type: Jezero Undae) Crater) Noachian "glowing Thin Hesperian terrain" Chloride layered deposits with deposits (type: Terra hydrated silica (type: Sirenum) Ophir Planum) Mg-Carbonate beds Interbedded sulfates (type: Nili Fossae) and clays (type: Gale Crater) 23 -23 Past Decade Results: Mars Planetary Evolution Proposed Chemical Environments Coupled phyllosian theiikian siderikian mineralogy and clays sulfates anhydrous ferric oxides morphology Deep define aqueous phyllosilicates environments Layered phyllosilicates Carbonate Their character deposits has evolved Phyllosilicate in fans indicating Plains sediments ? Chloride Deposits changing Intracrater environments clay-sulfates ? Meridiani layered Data support Valles layered ? ? the hypotheses Layered Hydrated ? Gypsum plains ? Silica but indicate greater Noachian Hesperian Amazonian complexity in Geologic Eras local ODY, MEX, MRO environments MGS MRO Major Questions for Mars and Planetary Science 1. What is the early evolution of the terrestrial planets, including Earth? What is the role of water in the early evolution? 2. Origin and evolution of life? 3. What are the key processes for short- and long-term climate change on terrestrial planets? 4. What is the internal structure and origin of the terrestrial planets? 26 Scientific Themes for Mars 1. Early evolution of the terrestrial planets, including Earth • Mars retains history that MGS has been completely erased from Earth (and Venus) • Earth’s oldest rocks >3.5 billion years old are rare and usually altered; Mars rocks exist at 4.5 billion years (determined from Ancient cratered surface of Mars (above) dating Mars meteorites) and remaining Earth crust from same time period (below) • This is the period of time when life evolved on Earth • As interpreted from chemical signatures in rock at 3.8 billion years; earliest microfossils are 3.0 billion years old. Scientific Themes for Mars 2. Origin and evolution of life questions Ancient life—interpreted potential has increased • Lots of ancient liquid water in diverse environments • Past geological environments that have reasonable potential to have preserved the evidence of life, had it existed. • Understanding variations in habitability potential is proving to be an effective search strategy • SUMMARY: We have a means to prioritize candidate sites, and reason to believe that the evidence we are seeking is within reach of our exploration. Modern life—interpreted potential still exists • Evidence of modern liquid water at surface is equivocal—probable liquid water in deep subsurface • Methane may be a critically important clue to subsurface biosphere • SUMMARY: We have