A BRIEF HISTORY OF EXTRASOLAR PLANET RESEARCH

The debate about the existence of other worlds has been ongoing for more than two millenia, but began in earnest during the last century. On many occasions over the past 70 years, “first” detections of extrasolar planets were announced, only to be dismissed as false. This graveyard of false claims shows us how the desire to make a groundbreaking discovery can often outpace proper scientific skepticism.

Most early searches for exoplanets involved astrometric surveys of nearby stars using "single dish" telescopes and photographic plates. As a planet orbits the host

star, it graviationally tugs the star in a counter-orbit. The planet can be detected and the orbit calculated by measuring the position of the host star relative to

background stars. Modern improvements include CCD detectors, space-based telescopes, and multi-dish interferometers. Of the 450+detections to date, only a handful of exoplanets have been confirmed by astrometry.

Transit detections require the fortuitous alignment of the orbital plane of the exoplanet so that the planet crosses directly across the star as seen from Earth. Ground-based transit searches have found dozens of "hot Jupiters", and the space-based COROT and Kepler missions are now turning up smaller planets.

Most extrasolar planets have been found using the Doppler velocity technique. Like astrometry, this technique relies on the gravitational tug of the planet on the host star. The planet is revealed by measuring periodic changes in the line-of-sight velocity of the star. The combination of transit and Doppler velocity measurements is sufficient to solve equations for the mass and radius of the planet, yielding the planet's bulk density. Three critical innovations have paved the way for the success of this technique: High resolution echelle spectrometers, CCD detectors, and high speed computers. Over the past 15 years these ongoing improvements have pushed the detection level from Jupiter to terrestrial mass planets.