Question

What are some ways in which scientists gather evidence of life on other planets?

While we may have many methods for detecting life on other planets, most (unfortunately) require us to physically visit the planet for direct testing. Our space probes and landers, however, can remotely provide us with a variety of tests for life and planet habitability. For example, the Viking mission to Mars in the mid-70s landed on the Red Planet equipped with an atmospheric water-vapor mapper as well as a mass spectrometer (a tool used in this case for organic substance detection in the Martian soil). Other past and current missions utilize similar technologies to sniff out possible biosignatures in planetary atmospheres and surfaces like water, oxygen, or methane. As far as other star systems are concerned (the closest being a 137,000-year trip for even our fastest rocket!), scientists are forced to rely on distance-observing methods to detect the possibility of life. For example, we have already detected approximately 100 Jupiter-like planets in other star systems, but current telescopes are still unable to detect Earth-like planets (imagine trying to find the light of a firefly in the beam of a searchlight). In 2006, NASA will launch the Kepler mission. The new telescope will be able to detect smaller Earth-sized bodies by accurately measuring how much a star dims when a smaller planet passes in front of it. For more on Kepler, check out: http://www.kepler.arc.nasa.gov/. The Terrestrial Planet Finder, expected to launch into orbit in the next decade, is hoped to directly detect planets. The TPF mission will mark the first time telescopes measure radiation from a planet instead of its parent star. Using two different methods of interferometry, the TPF will be able to block out the parent starlight and expose any Earth-like planets. In addition, the TPF will be able to “see” the composition of these far-away atmospheres, perhaps revealing evidence of extraterrestrial life. For more detail on the Terrestrial Planet Finder, please see: http://planetquest.jpl.nasa.gov/TPF/tpf_facts.html Anna Lee Strachan, NASA Astrobiology Institute
July 11, 2002