Copyright © 2007 Dorling Kindersley
Extraterrestrial life means life beyond Earth, or alien life. No life has been found on other planets in the Solar System, but it might exist on planets around other stars.
Life could be widespread on distant planets because the necessary elements, such as carbon, hydrogen, and oxygen, are common in space. A living planet also needs warmth, light, and an atmosphere. In SETI projects, astronomers are searching for intelligent life.
SETI stands for the Search for Extraterrestrial Intelligence. Astronomers tune in to radio waves from outer space, looking for coded signals that might come from other intelligent beings.