Session 3: Advances in Our Understanding of Mars New Understanding from Recent Missions

1. Session 3: Advances in Our Understanding of MarsNew Understanding fromRecent Missions Steve Squyres

2. Overview • Presentation is a high-level overview of findings from Mars missions since 2000 • MGS • Mars Odyssey • MER • Mars Express • Focus is on findings that are relevant to the search for evidence of former or present life

3. MGS: Gullies • MOC images show small-scale gullies. • Morphology is consistent with formation by flowing water. • Fresh morphology and lack of superimposed impact craters imply recent ages. • Gullies are concentrated on steep slopes at high latitudes. • Formation mechanism: • Seepage from subsurface aquifers? • Melting of snow?

5. MGS: Aqueous Sediments • MOC images show finely layered materials in many locations on Mars. • Some of the best examples are in closed topographic depressions (e.g., impact craters). • In a few instances, geologic relationships implicate liquid water as the fluid in which layered materials were transported and deposited. • There is at least one good example where deltaic morphology shows clear evidence of multiple episodes of water flow and sediment deposition.

7. Mars Odyssey: Ground Ice • Odyssey GRS results show very high concentrations of H at latitudes higher than 50-60º. • Depth of sampling is ~100 g cm-2. • Concentration is so high (equivalent H2O >50% by volume) that ground ice is the only reasonable explanation. • High-latitude regolith may be a major reservoir of H2O on Mars. • How deep does the ice go at high latitudes? • How deep do you have to go to find ice at lower latitudes? • Is it liquid at depth? • Does ground ice preserve organics by protecting them from oxidants?

9. Mars Odyssey: Low-Latitude Hydrogen • Odyssey GRS results also show significant concentrations of H (equivalent of ~5% H2O) at low latitudes. • Concentrations are high enough that they may require either heavily hydrated compounds or small amounts of ice.

10. MER: “MgSO4” Salt in Regolith • A trench in Gusev Crater shows strong evidence for subsurface “MgSO4” salt: • Strong correlation of Mg with S • Abundance lowest at surface, higher at base of trench, highest in trench wall • Soil ~5-10 cm below surface is ~15-20% “MgSO4” • Implications: • Dissolution of Mg-bearing rocks (olivine?) by S-bearing fluids (dilute H2SO4?) • Low levels of water migration through soil • Salts can be heavily hydrated, and could contain much of the low-latitude H seen by MGS if this is typical. • Salts are good freezing-point depressants.

12. MER: Aqueous Alteration at Gusev • Rocks in the Columbia Hills show evidence for interaction with water: • Highly elevated levels of S, Cl, K, P, Br • Basaltic chemistry, but highly oxidized and lacking in primary basaltic minerals • Goethite, an iron oxyhydroxide • Rocks are probably volcaniclastics or impact ejecta: • Finely to coarsely layered • Poorly sorted, with clasts up to several mm • IR spectrum fit well by basaltic glass

15. MER: Aqueous Alteration at Gusev (cont’d) • Implications: • Volcaniclastic or impact-generated rocks have interacted with water, but nature of interaction is not well understood • Hydrothermal? • Low-temperature? • Acid fog? • Little evidence that the water was related to the lake that once occupied Gusev Crater. May predate the lake. • Is this rock typical of ancient highland crust on Mars? • Gusev plains rocks are dry Hesperian basalts. The major aqueous activity at Gusev ended early.

16. MER: Water at Meridiani • Rocks at Meridiani Planum show evidence for aqueous deposition and diagenesis: • Pancam and MI images show fine sedimentary layering • Mini-TES spectra show abundant Ca and Mg sulfates • Mössbauer spectra show jarosite • APXS spectra show high S concentrations, implying that rocks are up to ~40% sulfate salts by mass • APXS spectra show highly variable Cl/Br ratios, consistent with formation by evaporation • Pancam and MI images show tabular vugs, consistent with crystal molds formed by aqueous minerals (e.g., gypsum?)

17. MER: Water at Meridiani (cont’d) • Rocks at Meridiani Planum show evidence for aqueous deposition and diagenesis: • Abundant spherules embedded within sedimentary rocks are dominated by hematite, and have morphologies and distributions consistent with formation as concretions. • Small-scale festoon-geometry cross stratification indicates deposition of some units in gently flowing liquid water. • Large-scale high-angle cross stratification indicates deposition of some units in an eolian environment (i.e., dunes).

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25. MER: Water at Meridiani (cont’d) • Rocks are a mixture of chemical and siliciclastic sediments with a complex diagenetic history. • Environmental conditions recorded include episodic inundation by shallow surface water, evaporation and desiccation. • Conditions were “habitable”, but could have posed significant challenges to the origin of life: • Highly saline? • Highly acidic? • Arid and only intermittently wet? • Aqueous precipitates (particularly concretions) on Earth are good at preserving fossil evidence of microbial life.

26. Mars Express: Methane • Mars Express PFS data suggest tens of ppb CH4 in the martian atmosphere. • Ground-based results (e.g., M. Mumma) support this observation, and show variations with latitude and surface temperature. • Residence time of CH4 is only hundreds of years, so a recent source is implied. • Potential sources include comets, outgassing, and life.

27. Mars Express: Recent Volcanism • Crater counts performed using HRSC image data show regions of extremely low crater density. • Claimed resurfacing ages are <10 Myr. • One can quibble over crater fluxes and absolute numbers, but there is little question that volcanic activity has been geologically “recent”. • Implications for: • Modern hydrothermal systems? • Recent outgassing?

29. Mars Express: Sulfates • Mars Express OMEGA results have shown evidence for sulfates (both Mg and Ca) in several locations • Meridiani Planum • Valles Marineris • HRSC images show that sulfates seen by OMEGA commonly correlate with layered rocks of sedimentary appearance. • Implication: Aqueous precipitates formed over a range of times and locations on Mars.