Exoplanets, The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way – Charley Lineweaver
Date: Wed. April 7th, 2004, 2:30 pm-3:30 pmLocation: Rockefeller 221
As we learn more about the Milky Way Galaxy, extrasolar planets and the evolution of life on Earth, qualitative discussions of the prerequisites for life in a Galactic context can become more quantitative. We model the evolution of the Milky Way Galaxy to trace the distribution in space and time of four prerequisites for complex life: the presence of a host star, enough heavy elements to form terrestrial planets, sufficient time for biological evolution and an environment free of life-extinguishing supernovae. We identify the Galactic habitable zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the Galactic center that widens with time and is composed of stars that formed between 8 and 4 billion years ago. This GHZ yields an age distribution for the complex life that may inhabit our Galaxy. We find that 75% of the stars in the GHZ are older than the Sun ( see Lineweaver, Fenner and Gibson, Science, January 2004, 303, 59). I will also discuss a new analysis of exoplanet data focused on answering the question “What Fraction of Sun-Like stars have planets?” In Lineweaver and Grether (2003, ApJ, 598, 1350) after correcting for observational selection effects we find that the data indicates that at least 25% (but possibly as much as 100%) of Sun-like stars possess planets.