![]() ![]() ![]() ![]() ![]() The analysis done here indicates that three-quarters of the Earth-like planets in the Universe are older than the Earth and that their average age is 1.8☐.9 billion years older than the Earth. I combine this probability with current estimates of the star formation rate and of the gradual buildup of metals in the Universe to obtain an estimate of the age distribution of Earth-like planets in the Universe. Here I quantify these effects and obtain the probability, as a function of metallicity, for a stellar system to harbor an Earth-like planet. Thus, there may be a Goldilocks selection effect: with too little metallicity, Earths are unable to form for lack of material with too much metallicity, giant planets destroy Earths. The presence of these close-orbiting giants is incompatible with the existence of Earth-like planets. Recent observations indicate that the presence of giant extrasolar planets at small distances from their host stars is strongly correlated with high metallicity of the host stars. They result from fusion inside stars and have been gradually building up over the lifetime of the Universe. These heavy elements, or “metals”, were not produced in the Big Bang. Planets such as the Earth cannot form unless elements heavier than helium are available. ![]()
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