{
  "note": "Per-environment habitability — where a known terrestrial extremophile could persist, judged against the cited limits of life. \"Control\" rows are deliberate has-water-but-not-habitable cases (Moon/Mercury cold traps, Venus clouds). Cited, confidence-tagged; NATURAL/PROCESSED, kept out of the baked tree.",
  "generatedAt": "2026-06-15",
  "bodies": 10,
  "environments": 13,
  "byVerdict": {
    "habitable": 4,
    "marginal": 4,
    "control": 3,
    "uninhabitable": 2
  },
  "limitsOfLife": [
    {
      "quantity": "upper temperature (replication)",
      "value": "122 °C (at 20 MPa)",
      "context": "Methanopyrus kandleri strain 116 (hydrogenotrophic methanogen)",
      "source": "Takai et al. 2008, PNAS"
    },
    {
      "quantity": "lower temperature (cell division)",
      "value": "−15 °C; metabolism to ~−25 °C",
      "context": "Planococcus halocryophilus, Arctic permafrost",
      "source": "Mykytczuk et al. 2013, ISME J"
    },
    {
      "quantity": "water activity floor",
      "value": "a_w 0.585 (xerophiles); ~0.611 (halophiles)",
      "context": "Aspergillus penicillioides; halophilic archaea",
      "source": "Stevenson et al. 2015/2017, Environ. Microbiol."
    },
    {
      "quantity": "ionizing radiation (acute LD10)",
      "value": "~15 kGy (liquid); ~140 kGy (desiccated/frozen)",
      "context": "Deinococcus radiodurans",
      "source": "Daly 2009, Nat. Rev. Microbiol."
    },
    {
      "quantity": "pressure (piezophiles)",
      "value": "active to ~110 MPa",
      "context": "Mariana-Trench / black-smoker isolates",
      "source": "Takai et al. 2008, PNAS"
    },
    {
      "quantity": "PP Special-Region threshold (operational)",
      "value": "255 K (−18 °C), a_w ≥ 0.60, 500-yr horizon",
      "context": "the lowest conditions a terrestrial organism is judged able to propagate on Mars",
      "source": "MEPAG SR-SAG2, Rummel et al. 2014"
    },
    {
      "quantity": "habitability gate (Ocean Worlds)",
      "value": "liquid water + CHNOPS + energy + conditions-in-range + < 1e-4 contact probability / 1000 yr",
      "context": "the NRC hierarchical decision tree",
      "source": "NRC 2012, Icy Bodies"
    }
  ],
  "table": {
    "EARTH": [
      {
        "region": "biosphere (the reference)",
        "conditions": "liquid water, energy, CHNOPS, T −20…122 °C across niches",
        "tolerant": "all",
        "limit": "within every limit",
        "verdict": "habitable",
        "confidence": "confirmed",
        "source": "the terrestrial biosphere (definitional reference)"
      }
    ],
    "ENCELADUS": [
      {
        "region": "subsurface ocean / hydrothermal seafloor",
        "conditions": "liquid water; H₂+CO₂ disequilibrium (chemical affinity ~50–120 kJ/mol); pH ~8.5–11; phosphates present; CHNOPS plausibly complete",
        "tolerant": "hydrogenotrophic methanogen, alkaliphile, psychro/piezophile",
        "limit": "methanogenesis energy yield well above maintenance; T/P/pH in range",
        "verdict": "habitable",
        "confidence": "confirmed",
        "source": "Waite et al. 2017, Science; Postberg et al. 2023, Nature"
      }
    ],
    "EUROPA": [
      {
        "region": "subsurface ocean / seafloor",
        "conditions": "global salt ocean; radiolytic oxidants (O₂, H₂O₂) over hydrothermal reductants → redox gradient; pH uncertain",
        "tolerant": "chemolithotroph, halophile, psychrophile",
        "limit": "redox energy availability (oxidant delivery vs ocean acidification)",
        "verdict": "habitable",
        "confidence": "inferred",
        "source": "Hand et al. 2007, Astrobiology"
      }
    ],
    "MARS": [
      {
        "region": "deep radiolytic subsurface",
        "conditions": "putative aquifers/brines at depth; radiolysis of water → H₂ + sulfate (Earth deep-biosphere analogue); UV-shielded; T near/above 255 K at depth",
        "tolerant": "chemolithotroph (H₂/sulfate-reducer), piezophile, psychrophile",
        "limit": "energy + liquid water (depth-dependent)",
        "verdict": "habitable",
        "confidence": "inferred",
        "source": "Tarnas et al. 2018, EPSL; 2021, Astrobiology"
      },
      {
        "region": "Special Regions / recurring slope lineae",
        "conditions": "transient perchlorate brines; freezing-point depressed but a_w typically < 0.60; intense UV + perchlorate toxicity",
        "tolerant": "halophile / perchlorate-tolerant (if any)",
        "limit": "a_w ≥ 0.60 (SR-SAG2) — most brines FAIL it; UV/perchlorate bactericidal",
        "verdict": "marginal",
        "confidence": "contested",
        "source": "Rummel et al. 2014; Wadsworth & Cockell 2017, Sci. Rep."
      },
      {
        "region": "shallow surface regolith",
        "conditions": "mean ~−60 °C, low pressure, a_w ≪ 0.6, lethal UV + GCR + perchlorates",
        "limit": "T, a_w, UV, radiation all exceed limits",
        "verdict": "uninhabitable",
        "confidence": "confirmed",
        "source": "SR-SAG2; Wadsworth & Cockell 2017"
      }
    ],
    "TITAN": [
      {
        "region": "subsurface water–ammonia ocean",
        "conditions": "deep liquid-water ocean (~10% NH₃ antifreeze); possible silicate-core contact; T near 0 °C at pressure; energy source poorly defined",
        "tolerant": "psychrophile, piezophile, ammonia-tolerant halophile",
        "limit": "liquid water + CHNOPS likely; energy/redox UNPROVEN",
        "verdict": "marginal",
        "confidence": "inferred",
        "source": "Iess et al. 2012, Science"
      },
      {
        "region": "surface hydrocarbon seas (Kraken/Ligeia)",
        "conditions": "~94 K, liquid methane/ethane — NO liquid water",
        "limit": "T and solvent far outside all terrestrial limits",
        "verdict": "uninhabitable",
        "confidence": "confirmed",
        "source": "Stofan et al. 2007, Nature (Titan lakes)"
      }
    ],
    "CERES": [
      {
        "region": "deep brine reservoir",
        "conditions": "regional/global brine ~40 km deep; Na-carbonate/NaCl/NH₄Cl; cryovolcanism ≤2 Myr ago; cold, salt-depressed liquid; weak energy/redox",
        "tolerant": "halophile, alkaliphile, psychrophile",
        "limit": "liquid persistence + a_w (salinity may push a_w low); energy limited",
        "verdict": "marginal",
        "confidence": "inferred",
        "source": "De Sanctis et al. 2020; Castillo-Rogez et al. 2020"
      }
    ],
    "GANYMEDE": [
      {
        "region": "subsurface ocean",
        "conditions": "salty ocean possibly sandwiched between ice layers (high-pressure ice below limits rock contact); deep",
        "tolerant": "psychrophile, piezophile",
        "limit": "energy + water–rock contact uncertain (HP-ice barrier)",
        "verdict": "marginal",
        "confidence": "inferred",
        "source": "Saur et al. 2015, JGR"
      }
    ],
    "MOON": [
      {
        "region": "polar permanently-shadowed cold traps",
        "conditions": "~40–100 K; water ice but NO liquid; no energy; no a_w",
        "limit": "T far below −20 °C; no liquid water",
        "verdict": "control",
        "confidence": "confirmed",
        "source": "Colaprete et al. 2010 — ice ≠ habitable"
      }
    ],
    "MERCURY": [
      {
        "region": "polar PSR cold traps",
        "conditions": "< 100 K ice + organics in permanent shadow; no liquid, no energy",
        "limit": "T; no liquid water",
        "verdict": "control",
        "confidence": "confirmed",
        "source": "Lawrence et al. 2013 — ice ≠ habitable"
      }
    ],
    "VENUS": [
      {
        "region": "cloud deck (~50–60 km)",
        "conditions": "~0–60 °C and ~1 bar (T/P fine!) but droplets are concentrated H₂SO₄ → a_w ~0.004, pH ~0",
        "tolerant": "extreme acidophile — still defeated by a_w",
        "limit": "a_w ~0.004 ≪ 0.585 floor (water activity, not temperature, is the killer)",
        "verdict": "control",
        "confidence": "confirmed",
        "source": "Hallsworth et al. 2021, Nat. Astron."
      }
    ]
  }
}