The Galactic Habitable Zone: Galactic Chemical Evolution

摘要: Abstract We propose the concept of a “Galactic Habitable Zone” (GHZ). Analogous to Circumstellar Zone (CHZ), GHZ is that region in Milky Way where an Earth-like planet can retain liquid water on its surface and provide long-term habitat for animal-like aerobic life. In this paper we examine dependence Galactic chemical evolution. The single most important factor likely terrestrial mass metallicity birth cloud. estimate, very approximately, at least half Sun required build habitable planet. has consequences interior heat loss, volatile inventory, loss atmosphere. A key issue production planets sustain plate tectonics, critical recycling process provides feedback stabilize atmospheric temperatures with oceans atmospheres. Due more recent decline from early intense star formation activity Way, concentration interstellar medium geophysically radioisotopes 40K, 235,238U, 232Th been declining relative Fe, abundant element Earth. Also are abundances Si Mg which affects core mantle All these elements isotopes vary time location Way; thus, planetary systems forming other locations times same as will not necessarily form planets. As result radial gradient, outer limit set primarily by minimum large Regions contain Earth-mass halo (including globular clusters), thick disk, thin disk. bulge should planets, but stars it have mix different Sun's. existence luminosity–metallicity correlation among galaxies all types means many too metal-poor Based observed luminosity function nearby visual passband, estimate (1) 1.3% luminous (and hence metal-rich) (2) about 23% typical ensemble metal-rich than average Way. zone be easily extrapolated universe whole, especially regard changing rate effect long-lived radioisotopes.