Research output: Contribution to journalArticle


The study of cosmology, galaxy formation, and exoplanets has now advanced to a stage where a cosmic inventory of terrestrial planets (TPs) may be attempted. By coupling semianalytic models of galaxy formation to a recipe that relates the occurrence of planets to the mass and metallicity of their host stars, we trace the population of TPs around both solar-mass (FGK type) and lower-mass (M dwarf) stars throughout all of cosmic history. We find that the mean age of TPs in the local universe is 7 ± 1 Gyr for FGK hosts and 8 ± 1 Gyr for M dwarfs. We estimate that hot Jupiters have depleted the population of TPs around FGK stars by no more than ≈10%, and that only ≈10% of the TPs at the current epoch are orbiting stars in a metallicity range for which such planets have yet to be confirmed. The typical TP in the local universe is located in a spheroid-dominated galaxy with a total stellar mass comparable to that of the Milky Way. When looking at the inventory of planets throughout the whole observable universe, we argue for a total of ≈1 × 1019 and ≈5 × 1020 TPs around FGK and M stars, respectively. Due to light travel time effects, the TPs on our past light cone exhibit a mean age of just 1.7±0.2 Gyr. These results are discussed in the context of cosmic habitability, the Copernican principle, and searches for extraterrestrial intelligence at cosmological distances.


  • Erik Zackrisson
  • Per Calissendorff
  • Juan González
  • Andrew Benson
  • Anders Johansen
  • Markus Janson
External organisations
  • Uppsala University
  • Carnegie Observatories
  • Stockholm University
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology


  • cosmology: miscellaneous, extraterrestrial intelligence, galaxies: formation, planets and satellites: terrestrial planets
Original languageEnglish
Article number214
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2016 Dec 20
Publication categoryResearch