7.2 Evidence for past water and potential habitability

Mars once had water, leaving behind clues in its landscape and minerals. Valley networks, outflow channels, and ancient lake basins suggest flowing water, while hydrated minerals like clays and sulfates indicate water-rock interactions. These features paint a picture of a wetter Martian past.

This evidence of water is crucial for understanding Mars' potential habitability. Liquid water, energy sources, and organic compounds could have supported life. Subsurface water ice offers hope for future exploration and possibly even current microbial life in protected environments.

Geomorphological Features and Mineralogical Evidence for Past Water on Mars

Geomorphological features of past water

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• Valley networks
  • Branching channels resembling river drainage systems on Earth (Nile River)
  • Formed by surface runoff from precipitation or groundwater seepage
• Outflow channels
  • Large, wide channels originating from chaotic terrains (Kasei Valles)
  • Formed by catastrophic flooding events or release of pressurized groundwater
• Deltas and alluvial fans
  • Sedimentary deposits at the mouths of valleys or channels (Eberswalde Crater)
  • Indicate the presence of flowing water and sediment transport
• Paleolakes
  • Ancient lake basins identified by inlet and outlet channels, shorelines, and sedimentary deposits (Gale Crater)
  • Suggest the presence of standing bodies of water in Mars' past
• Glacial features
  • Moraines, eskers, and other landforms associated with glacial activity (Deuteronilus Mensae)
  • Indicate the presence of ice and potential meltwater in the past

Mineralogical evidence for water

• Hydrated minerals
  • Phyllosilicates (clay minerals)
    • Formed by aqueous alteration of volcanic rocks (montmorillonite)
    • Indicate long-term interaction between water and rock
  • Sulfates
    • Formed by evaporation of water or hydrothermal activity (gypsum)
    • Suggest the presence of acidic, saline, or hydrothermal water
  • Carbonates
    • Formed in neutral to alkaline aqueous environments (magnesite)
    • Indicate the presence of more habitable water conditions
• Hematite spherules (blueberries)
  • Formed by precipitation from iron-rich water or alteration of iron-bearing minerals
  • Suggest the presence of liquid water and oxidizing conditions (Meridiani Planum)
• Geochemical evidence from rover missions
  • Elemental and isotopic compositions consistent with aqueous alteration
  • Indicate the interaction between water and rock, potentially favorable for habitability (Yellowknife Bay)

Habitability Potential and Significance of Water on Mars

Past habitable environments on Mars

• Liquid water
  • Essential for life as a solvent and medium for biochemical reactions
  • Geomorphological and mineralogical evidence suggests the presence of liquid water in Mars' past
• Energy sources
  • Chemical energy from redox gradients in aqueous environments (sulfur-iron reactions)
  • Potential for chemotrophic microbial life
• Organic compounds
  • Building blocks for life (amino acids, nucleobases)
  • Detected in small quantities by rover missions, indicating potential for prebiotic chemistry
• Neutral to alkaline pH
  • More favorable for life compared to acidic conditions (pH 7-8)
  • Presence of carbonates and phyllosilicates suggests the existence of habitable water conditions
• Protection from radiation
  • Subsurface environments, such as caves or deep groundwater, provide shielding from harmful radiation (cosmic rays, UV)
  • Potentially more habitable than surface environments

Subsurface water ice for exploration

• Water ice reservoirs
  • Substantial amounts of water ice detected in the Martian subsurface, particularly at mid to high latitudes (Utopia Planitia)
  • Radar evidence for liquid water beneath the South Polar Layered Deposits
• Resource for human exploration
  1. Water ice can be extracted and purified for drinking, hygiene, and agriculture
  2. Electrolysis of water can produce oxygen for breathing and hydrogen for fuel
• Implications for habitability
  • Subsurface water ice may provide a potential habitat for microbial life (psychrophiles)
  • Melting of ice could create transient liquid water environments
• Accessibility
  • Future missions can target water ice reservoirs for in-situ resource utilization (ISRU)
  • Subsurface drilling and extraction technologies need to be developed for efficient access to water ice (ExoMars drill)