1. 1 Life in the Universe Life is present on Earth nearly everywhere even under the most extreme conditions. Life survives in boiling hot springs and in permanently frozen tundra. Life can be found in the perpetual darkness and crushing pressures on the ocean floor. Given these extremes, can life exist on other planets or moons in our Solar System and around other stars? Is Earth the only home for life in the Universe?

2. 2 The Search for Life - Mars Among all of the planets besides Earth, only Mars appears to have had conditions that might have been suitable for life. What appear to be dry lake beds and forms of water erosion appear on the surface. If liquid water once existed on the surface of Mars did life also? Might it still be there?

3. 3 The Search for Life - Mars In 1976 the U.S. sent two robotic landers to study the surface of Mars to search for signs of life. Chemical analysis of the soil found no signs of life. In 1996 meteorites found in Antarctica were determined to be from Mars. These rocks appeared to contain fossilized bacteria. Not all scientists are convinced these are bacteria, however. Several new missions to Mars are planned in the next few years to continue the search. A picture of Mars and the foot pad of the Viking lander.

4. 4 The Search for Life Elsewhere in Our Solar System Other places in our Solar System where life is thought to be possible are: –beneath the thick ice on Europa. Europa may have an ocean beneath the ice. –on the surface of Titan. Titan has a thick atmosphere composed of gases similar to that thought to exist on Earth. Missions are being planned to Europa and the Huygens probe will land on Titan in 2004. Europa

5. 5 The Search for Life Around Other Stars By measuring small Doppler shifts in the spectra of stars, astronomers have discovered almost 100 planets. So far these planets are estimated to be as large as Jupiter or Saturn. No planets the size of Earth have been found yet. As technology improves astronomers expect to be able to find smaller planets and perhaps to observe them directly for signs of life.

6. 6 SETI Some astronomers have begun to search for signals coming from intelligent life elsewhere. The Search for Extra Terrestrial Intelligence (SETI) is collecting radio data and searching for patterns that seem artificial. This difficult process requires lots of data and lots of computing time. The SETI@home project enables anyone with a computer to help in the search.