When the Solar System was born about 4.6 billion years ago only 8% of the potentially habitable terrestrial exoplanets that will ever form in the Universe existed. This theoretical conclusion is based on an assessment of star-birth data gathered by the NASA/ESA Hubble Space Telescope and planet surveys carried out by NASA’s Kepler/K2 mission. An artist’s impression of innumerable potentially habitable terrestrial exoplanets that have yet to be...