The search could target biosignatures, such as oxygen and methane in the atmospheres of planets around them, or technosignatures, such as radio or laser transmission, industrial pollution or city lights.Ī second method is to search for early technological civilizations that produced powerful beacons of light or transformed their environment in ways that are detectable across cosmological distances. One approach is to search for signatures of life around older stars in our Milky Way galaxy. Can we find evidence for earlier participants in the cosmic story of life? It is therefore difficult to imagine that we are the first advanced civilization to appear on the cosmic scene.
Nevertheless, many sunlike stars with a similar heavy element abundance must have formed long before the sun because we see the products of their death as white dwarfs. Given this proximity, Earth-like planets would have their atmosphere stripped by stellar winds or their surface sterilized by UV flares from these dwarf stars. Second, dwarf stars are fainter, bringing their habitable zone closer in. This includes the heavy elements that make rocky planets like the Earth, as well as the oxygen and carbon needed for water-based organic chemistry. First, the material that assembled to make early stars lacked the heavy elements that are essential for life as we know it. If this mediocrity principle applies to all of our cosmic circumstances, then there must be physical reasons for why our particular form of intelligent life did not arise around an early or dwarf star. It stems from the discovery made half a millennium ago by Nicolaus Copernicus that we are not located at the physical center of the cosmos as thought previously. The Copernican principle asserts that we are not privileged observers of our universe.
Why were we born so late in cosmic history around a relatively massive star like the sun? Statistically speaking, we were more likely to exist earlier or around a lower-mass star. Moreover, most stars formed billions of years before the sun, based on the observed star formation history since the big bang.
Most stars are one tenth as massive and will live hundreds of times longer than the sun.