Physics and the Search for ET

How physics contributes to the scientific search for extraterrestrial life elsewhere in the universe.

Is there anyone out there or are we alone in the universe? We don't yet know, but physics is an important tool in finding out. For questions about life, most people normally think of biology, biochemistry, and similar sciences. However the best ways to search for extraterrestrial life combine all areas of science.

The search for life in the solar system involves sending robotic probes to other planets, mostly Mars. After landing, the probes rely on biochemistry to search for life. However getting the probe to another planet involves quite a bit of physics, such as rocket propulsion and orbital mechanics.

Outside the solar system, searches for life have traditionally looked for radio signals from possible extraterrestrial civilizations. That uses the physics of electromagnetic radiation. Special relativity and the speed of light limit keeps us from sending probes to other stars.

The April 2008 Scientific American has a nice article about a new strategy. Author Nancy Kiang discusses work that she and coworkers are doing on strategies for detecting vegetation on extrasolar planets. We have detected water on extrasolar planets using spectroscopy. Why not try to detect lush vegetation on a planet with similar techniques. NASA satellites use this tool and the spectral signature of chlorophyll to map vegetation on Earth. Increasing sensitivity and resolution might allow us to try this on extrasolar planets.

The trick is that plant life on extrasolar planets may have different spectral signatures. The green pigments on Earth plants are most efficient for the Sun's energy spectrum. Planets orbiting stars of different temperatures will have different spectra of natural light. Therefore plants on these planets are likely to have a different color chlorophyll and different spectral signatures. Knowing the physics of blackbodies is crucial to this analysis.