Question

Can we detect microbial or other non-intelligent life on planets outside of our solar system?

Given the current level of human technology, the short answer to your question is no—but within the next 10-20 years, we might be able to do so. In general, there are two ways of detecting any type of extraterrestrial life: direct detection and remote sensing. Direct detection usually involves going to a planet and taking measurements to look for life (like the Viking mission experiments on Mars in the 1970s). However, direct methods are infeasible for finding life on extrasolar planets, because it would take a very long time to travel to other star systems using existing propulsion methods. Thus, to detect life beyond the solar system, we must rely on remote sensing. A SETI-type search is currently the only way to find life on extrasolar planets, but that would only allow us to find technological life. (SETI is the Search for Extraterrestrial Intelligence, which looks for signals from other planets that can only be transmitted by technological civilizations.) In the future, we hope to find signs of life on extrasolar planets by looking for atmospheric gases that are indicative of biological processes—such gases are often called biosignatures. If we were remotely looking at an Earth-like planet’s atmosphere, strong biosignatures would be ozone (O3) and oxygen (O2); another possible biosignature would be methane (CH4). All three of these gases can be viewed as biosignatures of non-technological life. Remote detection of atmospheric biosignatures on extrasolar planets is a major goal of NASA’s planned Terrestrial Planet Finder mission, which will be launched in about 10 years (see http://tpf.jpl.nasa.gov). One very important thing to remember is that we need strong scientific evidence before claiming that we have found extraterrestrial life! Pushker Kharecha Doctoral Student in Geosciences, Penn State University
May 31, 2002