Chapter #1: A Universe of Life?

1.1 The Possibility of Life Beyond Earth

What are we searching for?

* What are we looking for exactly? * Is it: intelligent life portrayed in sci-fi, more akin to the plants and animals we see in parks or zoos, or is it tiny bacteria-like microbes? * The simple answer to this question is “all of the above” * Extraterrestrial life: Life beyond Earth, we are looking for any sign of life, be it simple, complex, or even intelligent * We have a general definition of what life is, but for now it should be clear that this is a complicated question that affects how we search for life in the universe * Because of the definitional difficulty, the scientific search for extraterrestrial life in the universe generally presumes a search for life that is at least somewhat Earth-like and that we could therefore recognize based on what we know from studying life on Earth

Is it reasonable to imagine life beyond Earth?

* Prior to the 20th century, for example, some scientists guessed that Venus might harbor a tropical paradise -> this guess was based on little more than the fact that Venus is covered by clouds and closer than Earth to the Sun * Mars was the subject of even more intense debate, largely because a handful of scientists thought they saw long, straight canals on the surface * These canals, which don’t actually exist, were cited as evidence of a Martian civilization * Why has scientific interest in life beyond Earth exploded in the past few decades? * Although large, multi-cellular life in our solar system seems unlikely anywhere but on Earth, new discoveries in both planetary science and biology have given us some reason to think that simpler life – perhaps tiny microbes – might yet exist on other planets and moons that orbit our Sun * We have only