How many stars, what types, and how densely packed? These set the grid's baseline.

• [Mamajek] Number Densities of Stars by Type in the Solar Vicinity
  Rochester Memo avgStarsPerTile = 2.89 pctSunLike = 0.17
• [Rybizki & Just 2017] Stellar Inventory of the Solar Neighbourhood using Gaia DR1
  arXiv stellar density calibration
• [Bovy & Rix 2013] Milky Way Disk Surface Density Profile
  arXiv disk density modeling
• [Widmark et al. 2025] Counting Mass with Gaia
  arXiv Gaia-based densities

What fraction of stars have rocky planets in the habitable zone with liquid water?

• [Bryson et al. 2021] The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data
  arXiv / AJ pctHabitablePlanet = 0.40
• [Petigura et al. 2013] Prevalence of Earth-size planets orbiting Sun-like stars
  PNAS foundational Kepler eta-Earth
• [Kepler FGK Survey] Searching the Entirety of Kepler Data: Occurrence Rate Estimates for FGK Stars
  AJ refined occurrence rates
• [Scherf & Lammer 2024] Eta-Earth Revisited II
  Astrobiology updated eta-Earth
• [Bonati et al. 2024] Water content of rocky exoplanets in the habitable zone
  A&A pctWater = 0.75
• [Stern & Gerya 2024] The importance of continents, oceans and plate tectonics for the evolution of complex life
  Nature Scientific Reports plate tectonics filter
• [Vilovic et al. 2025] Superhabitable Planets Around Mid-Type K Dwarf Stars
  Astronomische Nachrichten K-dwarf advantage

How likely is it that life arises on a suitable planet? Bayesian evidence increasingly favors rapid emergence.

• [Kipping 2025] Strong Evidence That Abiogenesis Is a Rapid Process on Earth Analogs
  arXiv pAbiogenesis = 0.70 13:1 Bayesian odds
• [Chen & Luo 2025] The Abiogenesis Timescale
  arXiv >91% short timescale
• [Kipping 2020] An objective Bayesian analysis of life's early start and our late arrival
  PNAS 3:1 rapid abiogenesis
• [Spiegel & Turner 2012] Bayesian analysis of the astrobiological implications of life's early emergence on Earth
  PNAS foundational Bayesian framework
• [Lingam, Nichols & Balbi 2024] A Bayesian Analysis of the Probability of the Origin of Life Per Site Conducive to Abiogenesis
  Astrobiology per-site probability
• [Moody et al. 2024] The nature of the last universal common ancestor and its impact on the early Earth system
  Nature Ecology & Evolution LUCA at 4.2 Gya
• [Pearce & Pudritz 2017] Origin of the RNA world: The fate of nucleobases in warm little ponds
  PNAS warm pond model
• [Bains et al. 2024] Alternative solvents for life: framework for evaluation
  arXiv alternative solvents

How long does it take to go from microbes to minds? And is technology inevitable once intelligence evolves?

• [Lane & Martin 2015] Eukaryogenesis, how special really?
  PNAS eukaryogenesis bottleneck
• [Nature 2025] Dated gene duplications elucidate the evolutionary assembly of eukaryotes
  Nature eukaryote assembly timeline
• [Snyder-Beattie et al. 2025] A reassessment of the hard-steps model for the evolution of intelligent life
  Science Advances pIntelligent = 0.10
• [Convergent Evolution] Convergent evolution of complex brains and high intelligence
  Phil. Trans. R. Soc. B 9+ independent origins
• [Royal Society 2025] An early origin of oxygenic photosynthesis delays the Great Oxidation
  Phil. Trans. R. Soc. B photosynthesis timeline

Can we detect alien radio signals? How far does Earth's own signal reach?

• [Sheikh et al. 2025] Earth Detecting Earth
  arXiv radioLifetime detection range
• [Saide et al. 2023] Simulation of Earth's Radio Leakage from Mobile Towers
  MNRAS detectable at ~6 ly
• [COSMIC/VLASS 2025] COSMIC technosignature search
  arXiv latest SETI results
• [Haqq-Misra et al. 2024] Artificial Greenhouse Gases as Exoplanet Technosignatures
  arXiv alternative detection

Statistical frameworks for estimating the number of detectable civilizations.

• [Sandberg, Drexler & Ord 2018] Dissolving the Fermi Paradox
  arXiv uncertainty propagation
• [Prantzos 2020] A probabilistic analysis of the Fermi paradox in terms of the Drake formula
  MNRAS L parameter dominance
• [Carroll-Nellenback et al. 2019] The Fermi Paradox and the Aurora Effect
  AJ settlement dynamics
• [Garrett 2024] Is artificial intelligence the great filter?
  arXiv AI as filter
• [Haqq-Misra & Baum 2009] The Sustainability Solution to the Fermi Paradox
  arXiv sustainability constraints
• [Crawford & Schulze-Makuch 2023] Is the apparent absence of extraterrestrial technological civilizations down to the zoo hypothesis or nothing?
  Nature Astronomy zoo hypothesis

Dyson spheres, beacons, and post-biological intelligence — the DLC scenarios.

• [Dyson 1960] Search for Artificial Stellar Sources of Infrared Radiation
  Science Dyson sphere concept
• [Wright et al. 2014] The G-HAT Infrared Search for ETI
  arXiv systematic Dyson search
• [Suazo et al. 2022] Project Hephaistos I: Upper limits on partial Dyson spheres
  MNRAS Dyson sphere candidates
• [Suazo et al. 2024] Project Hephaistos II: Dyson sphere candidates
  MNRAS updated candidates
• [Benford et al. 2008] Messaging with Cost Optimized Interstellar Beacons
  arXiv beacon design
• [Sandberg, Armstrong & Cirkovic 2017] That is not dead which can eternal lie: the aestivation hypothesis
  arXiv aestivation hypothesis
• [Cirkovic & Bradbury 2006] Galactic gradients, postbiological evolution and SETI
  arXiv post-biological intelligence

If civilizations expand, how fast and how far?

• [Carroll-Nellenback et al. 2019] The Fermi Paradox and the Aurora Effect
  AJ settlement wave dynamics
• [Forgan 2017] The Galactic Club, or Galactic Cliques?
  arXiv network topology
• [Forgan 2011] Spatio-temporal Constraints on the Zoo Hypothesis
  arXiv zoo hypothesis modeling
• [Jebari & Asker 2024] Saved by the Dark Forest
  The Monist dark forest game theory