Question

What are three methods we are using to detect other planets outside of our solar system?

There are currently about 80 known planets outside of our solar system. The three methods that have been used to find these extrasolar planets are pulsar timing, radial velocity measurements, and photometry. The first discovery of extrasolar planets in 1991 was based on pulsar timing, in which slight delays in the arrival times of radiation pulses from a pulsar are used to infer the gravitational presence of orbiting planets. The first planet discovered around a Sun-like star was detected in 1995 using the radial velocity method, in which wavelength shifts in the star’s light (due to the Doppler effect) are used to infer the gravitational presence of planets. Except for the pulsar planets, all known extrasolar planets were found using the radial velocity method. The third method, photometry, was successfully used in 1999 (actually, it was used on a planet that was already discovered by the radial velocity technique). Photometry relies on planetary transits, which occur when a planet passes in front of its star. When this happens, the planet blocks part of the star’s light, which lets us figure out how large the planet is. Other indirect methods that could be used in the near future to detect extrasolar planets are astrometry and gravitational microlensing. So far, pulsar timing is the only method that has been able to find Earth-sized extrasolar planets. In time, direct detection and imaging of extrasolar planets will be possible as well, through space-based missions (see http://origins.jpl.nasa.gov/missions/sbobs.html). Pushker Kharecha Doctoral Student in Geosciences, Penn State University
May 31, 2002