Dead Zones for Life in the Universe
From our privileged position on a planet teeming with life, we can wonder about the possiblity of advanced life elsewhere in the universe. Ward and Brownlee catalog some places where you would not expect such life, for the indicated reasons.
- Early universe: the most distant known galaxies represent galaxies formed early in the history of the universe. As such they would not have had time for sufficient heavy element production to support life. Stars in such galaxies would not have enough heavy elements to form Earth-size inner planets.
- Globular clusters: Even though globular clusters like Omega Centauri may have a million or more stars, they are too metal poor to have inner planets as large as the Earth. The dearth of "metals" indicates great age, so solar mass stars may have evolved to the red giant stage which would be too hot for life on inner planets. Globular clusters often have such high star density that the orbits of planets would be disturbed.
- Elliptical galaxies: like globular clusters, the stars are too metal poor to produce Earth-like planets.
- Small galaxies: the production of heavy elements is too small to provide the raw material to produce Earth-like planets.
- Centers of galaxies: energetic processes would impede the development of life. Too much ionizing radiation.
- Edges of galaxies: the stars would be too metal-poor.
- Planetary systems with giant planets in elliptical orbits: the planets would so severely perturb inner rocky planets that advanced life could not form.
- Future stars: Uranium, thorium and potassium may be too rare to provide the necessary planet heating to drive plate tectonics.
Habitable planet concepts
Ward & Brownlee