TERRESTRIAL PLANETS ACROSS SPACE and TIME

Summary, in English

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 TP_s around both solar-mass (FGK type) and lower-mass (M dwarf) stars throughout all of cosmic history. We find that the mean age of TP_s 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 TP_s 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.