Small galaxies Centers of galaxies Edges of galaxies Planetary systems with "hot Jupiters"
The most distant known galaxies are too young to have enough metals for formation of Earth-size inner planets. Hazards include energetic quasar-like activity and frequent supernova explosions.
Although they contain up to a million stars they are too metal-poor to have inner planets as large as Earth. Solar-mass stars have evolved to giants that are too hot for life on inner planets. Stellar encounters perturb outer planet orbits.
Stars are too metal-poor. Solar-mass stars have evolved into giants that are too hot for life on inner planets.
Most stars are too metal-poor.
Energetic processes impede complex life.
Many stars are too metal-poor.
Inward spiral of giant planets drives the inner planets into the central star.
Planetary systems with giant planets in eccentric orbits
Environments too unstable for higher life. Some planets lost to space.
Uranium, potassium and thorium are perhaps too rare to provide sufficient heat to drive plate tectonics.
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