Mars
Habitability Score
Once covered in liquid oceans, Mars harbors subsurface water ice, seasonal methane spikes, and minerals that sustained life on early Earth — making it the most studied candidate in astrobiology.
Overview
Mars is humanity's most visited neighbor and our most studied candidate for past or present life beyond Earth. For decades it sat at the center of every major astrobiology discussion, and for good reason: the evidence suggesting Mars was once a warm, wet world just keeps piling up.
Evidence for Habitability
Ancient Liquid Water
Orbital imagery and rover data confirm that Mars had vast river systems, lake beds, and possibly an ocean covering its northern hemisphere more than 3 billion years ago. The Curiosity rover found ancient mudstone in Gale Crater containing organic molecules — the chemical building blocks life uses everywhere on Earth.
Subsurface Water Today
The Mars Express spacecraft used radar (MARSIS) to detect what appears to be a 20 km-wide subglacial liquid water lake beneath the south polar ice cap. Subsequent studies have hinted at multiple such pockets. Liquid water — even briny, perchlorate-rich water — is the single most important prerequisite scientists look for.
Methane Fluctuations
Both the Curiosity rover and ESA's Trace Gas Orbiter have detected periodic spikes of methane in the Martian atmosphere. On Earth, roughly 90% of atmospheric methane is biological in origin. The Martian spikes are not yet explained by purely geological processes, though volcanic activity remains a candidate.
Minerals That Hosted Life on Earth
Perseverance rover in Jezero Crater (an ancient river delta) has found carbonates, serpentinite, and olivine — minerals associated with hydrothermal systems on early Earth that are thought to have been incubators for the first microbial life.
Challenges
- Surface radiation is intense (no global magnetic field)
- Average surface temperature: –60 °C
- Atmospheric pressure is less than 1% of Earth's
- Perchlorate salts in soil are toxic to most known life
Why Scientists Are Optimistic
If life ever arose on Mars, it may have retreated underground — protected from radiation by meters of rock, kept liquid by geothermal heat, and fed by chemical reactions between water and minerals. Deep subsurface extremophiles (like those in Earth's deep mines) represent the most plausible model for any extant Martian life.
Current and Future Missions
- Perseverance (NASA) — collecting rock samples for future return to Earth
- ExoMars / Rosalind Franklin (ESA/Roscosmos) — drilling up to 2m below surface to search for biosignatures
- Mars Sample Return — planned joint NASA/ESA mission to bring collected samples back for Earth-based analysis