Extraterrestrial life is defined as the past or present existence of life forms outside of our home planet of the Earth. The study of life in outer space is called astrobiology or xenobiology.

Most astrobiologists think that if extraterrestrial life exists then it occurs independently in different places. Other scientists contend that extraterrestrial life could have occurred in one place and spread across the universe.

The search for extraterrestrial life has been going on over four decades with the Search for Extra-Terrestrial Intelligence (SETI) project, which is a group of efforts coordinated by the SETI Institute. It is dedicated to scientific research and education concerning the origin and prevalence of life in the universe. Its search centers on looking for life with an intelligence, which can send out some type of signal that can be picked up with our equipment and instruments. The home website of SETI is: http://www.seti.org.

Astronomers are also searching for extrasolar planets (or exoplanets), those planets that exist outside of the Earth’s solar system. These searches are concentrating on finding evidence of planets potentially conducive to life, such as those that contain an atmosphere with oxygen, liquid water, and are within a star’s habitable zone (not too close or too far away from it host star).

One of these searches found Gliese 581 c. More information about this Earth-like exoplanet is found at the ITwire article “Earth-like planet found around star Gliese 581, 20.5 LYs away” at http://www.itwire.com.au/content/view/11577/1066/.

Some present and future missions dedicated to finding exoplanets include the Darwin mission. It is a space mission headed by the European Space Agency (ESA) to directly discover Earth-like planets. It is scheduled to launch on or after 2020. More information about Darwin is found at: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=28.

The French Space Agency launched the COROT (COvection Rotation and planetary Transits) mission on December 27, 2006 with a Soyuz rocket. It is currently looking for large extrasolar planets. Read more about COROT from Itwire article “Exoplanet Search Begins with French Launch of Corot Telescope Satellite” at http://www.itwire.com.au/content/view/8299/1066/.

The Kepler mission, scheduled to be launched in November 2008, was developed by NASA to search for extrasolar planets over a four-year period. The space observatory will concentrate on periodic transits of possible planets in front of about 100,000 stars to detect a variable brightness in the stars. Kepler will look for Earth-sized and smaller planets. The Kepler mission will be placed in an Earth-trailing orbit about the Sun. It will have a mass of about 2,290 pounds (1,039 kilograms), an aperture of 3.11 feet (0.95 meters), and a primary mirror of 4.59 feet (1.4 meter). More information about Kepler is found at: http://kepler.nasa.gov/.

Astronomers are also looking for celestial bodies within our solar system and in nearby star systems.

The planet Mars could possibly have possessed liquid water in the past and it may still possess liquid water beneath the surface. Read the ITwire article about possible subsurface water at: “Mars Express scientists think Mars might have plenty of water underground” (http://www.itwire.com.au/content/view/8959/1066/) and “First probe beneath Mars surface finds water ice” (http://www.itwire.com.au/content/view/10553/1066/).

The Alpha Centauri system is the closest star system to the Sun. Two of its three stars (Alpha Centauri A and Alpha Centauri B) are similar to the characteristics of the Sun. They are only about 4.36 light-years away. The third member of the triple-star system is a red dwarf star called Proxima Centauri, which is about 4.22 light-years away. Scientists have used computer programs to show that terrestrial planets could form on Alpha Centauri A and Alpha Centauri B. For more information about the Alpha Centauri system go to “Alpha Centauri: A Candidate for Terrestrial Planets And Intelligent Life” (http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html).

Within our solar system, the following planets and moons could harbor microbial life.

The Galileo mission has explored Jupiter and its moons Europa, Ganymede, and Callisto:

“Jupiter Moon May Have Life -- Experts Urge a Mission”: http://news.nationalgeographic.com/news/2005/03/0323_050323_jupitereuropa.html.

“Is There Ocean Life on Jupiter's Moons?”: http://www.spacetoday.org/SolSys/Jupiter/JupiterOceans.html

“Galileo Project”: http://www2.jpl.nasa.gov/galileo/.

The Cassini spacecraft is exploring Saturn and its moons Enceladus and Titan.

“Liquid water on Saturn moon could support life”: http://www.msnbc.msn.com/id/11736311/

“Hot Start model supports possible life on Saturn’s Enceladus”: http://www.itwire.com.au/content/view/10424/1066/

Cassini-Huygens: Mission to Saturn and Titan: http://saturn.jpl.nasa.gov/home/index.cfm.

Will we find extraterrestrial life? Only the future will hold that answer and only if we continue to search and explore and learn!

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Astronomy  ESA  Mars  NASA  Research  Science  Space  Sun  Universe  William Atkins