The question of whether or not other planetary systems similar to our own exist has intrigued astronomers and the general public alike for centuries. It was only in the in the 1990s that astronomers began to discover direct evidence for planets outside the solar system.

Method of Detection

The planets of the solar system are visible because of the sunlight that they reflect. Unfortunately, planets that orbit other stars are far too faint relative to their stars for current astronomical telescopes to observe them directly as faint points of light next to their much brighter stars. Instead, astronomers use a variety of techniques to indirectly infer the presence of these extrasolar planets.

The method by which all of the known extrasolar planets have been discovered is the radial velocity (or Doppler) technique. The mass of the orbiting planet causes the central star to be pulled around...