FIRST STOP: The Transit Method
Astronomers also look for variations in the timing of a particular planet's transit, because these can reveal the presence of additional worlds orbiting the same star.
NEXT: Wobbling Stars
Several teams of astronomers have discovered many exoplanets using this method and such Earth-based instruments as the HARPS spectrograph, on a telescope at the European Southern Observatory's La Silla Observatory in Chile, and the HIRES spectrograph, on Hawaii's Keck telescope.
NEXT: Gravitational Microlensing
This produces a light curve — a brightening and fading of the faraway star's light over time — whose characteristics tell astronomers a lot about the foreground object, which is often a star. If this star has any planets, these can generate secondary light curves, alerting researchers to their presence.
Gravitational microlensing is less biased toward planets that orbit relatively far from their stars than the transit or radial velocity methods. Researchers have even used it to find so-called "rogue planets," which cruise through the depths of space without a parent star.
NEXT: Direct Imaging
NASA's Hubble Space Telescope has spotted planets by direct imaging, as have Hawaii's Keck Observatory, the European Southern Observatory's Very Large Array in Chile and several other telescopes.
NEXT: Pulsar Timing
Anomalies in the timing of these radio pulses can reveal the presence of orbiting planets. The first worlds ever discovered beyond our solar system were found using this method back in 1992.
NEXT: Harnessing Special Relativity
The planet Kepler-76b (also known as "Einstein's planet") was discovered via this method, then confirmed by radial velocity measurements. More such detections are likely to follow as researchers hone the technique.
Scientists have searched for alien planets using astrometry for decades, with very limited (and debatable) success. But the European Space Agency's Gaia mission, set to launch in October 2013, could spot tens of thousands of exoplanets using the technique, researchers say.