Space Telescope Science
Astronomers are conducting extensive observations to estimate how many planets in our Milky Way galaxy might be potential abodes for life. These are collectively called "Earth-like" – in other words, Earth-sized worlds that are at the right distances from their stars for moderate temperatures to nurture the origin of life. The search for extraterrestrial intelligent life in the universe (SETI) is based on the hypothesis that some fraction of worlds, where life originates, go on to evolve intelligent technological civilizations. Until we ever find such evidence, Earth is the only known abode of life in the universe. But the universe is not only vastly big, it has a vast future. There is so much leftover gas from galaxy evolution available that the universe will keep cooking up stars and planets for a very long time to come. In fact, most of the potentially habitable Earth-like planets have yet to be born. This theoretical conclusion is based on an assessment of star-birth data collected by the Hubble Space Telescope and exoplanet surveys made by the planet-hunting Kepler space observatory.