7.1 Mars' past and present environment

Mars, once a potentially habitable world, has undergone dramatic changes. Its early environment featured a thicker atmosphere, warmer climate, and liquid water on the surface. These conditions could have supported microbial life, making Mars a prime target for astrobiology.

Today, Mars presents a harsh landscape with a thin atmosphere and extreme temperatures. Despite these challenges, the possibility of subsurface water and potential microbial habitats keeps the Red Planet at the forefront of the search for extraterrestrial life.

Mars' Current Environment

Characteristics of Mars' environment

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• Atmosphere
  • Thin atmosphere primarily CO2 (95.3%), N2 (2.7%), and Ar (1.6%)
  • Surface pressure 0.6% of Earth's average
  • Minimal protection against solar radiation and meteorite impacts
• Climate
  • Cold and dry, average surface temperature -63°C (-82°F)
  • Significant temperature variations between day/night, latitudes, and elevations
  • Seasonal changes due to tilted axis cause variations in temperature, pressure, and polar ice cap size
• Geology
  • Diverse surface features include impact craters, volcanoes (Olympus Mons), canyons (Valles Marineris), and dry riverbeds
  • Water ice present at poles and in subsurface deposits

Mars' Environmental Changes and Habitability

Evolution of Martian conditions

• Early Mars (4.1 to 3.7 billion years ago)
  • Evidence suggests thicker atmosphere, warmer and wetter climate
  • Liquid water on surface indicated by ancient river valleys and lake basins
• Factors contributing to environmental changes
  • Loss of magnetic field led to atmospheric stripping by solar wind
  • Reduced volcanic activity decreased atmospheric replenishment
  • Cooling interior reduced outgassing and atmospheric density
• Transition to current cold, dry state
  • Thinning atmosphere caused surface water to evaporate or freeze
  • Reduced greenhouse effect further cooled the planet

Past vs present Mars habitability

• Past environment
  • Warmer, wetter climate with thicker atmosphere
  • Liquid water on surface (ancient river valleys and lake basins)
  • Potentially habitable for microbial life
• Present environment
  • Cold, dry climate with thin atmosphere
  • Water primarily as ice at poles and in subsurface
  • Harsh surface conditions (intense UV, oxidizing soil)
  • Subsurface environments may still harbor microbial life
• Implications for habitability
  • Past conditions more favorable for emergence and survival of life
  • Current surface challenging for life as we know it
  • Subsurface (aquifers, geothermal regions) may support microbial life

Volcanic and tectonic influences

• Volcanic activity
  • Olympus Mons and other shield volcanoes indicate extensive past volcanism
  • Outgassing contributed to early atmosphere
  • Lava flows and ash deposits reshaped surface
• Tectonic activity
  • Valles Marineris and other features suggest past crustal deformation
  • Tharsis bulge volcanic plateau likely influenced global tectonics
  • Limited evidence for plate tectonics unlike Earth
• Role in shaping environment
  • Volcanism released greenhouse gases, contributing to early warmer climate
  • Outgassing replenished atmosphere, offsetting solar wind losses
  • Tectonics influenced distribution of volcanism and surface water
  • Lack of sustained plate tectonics may have limited long-term atmospheric stability and habitability compared to Earth