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Since the first alien planets were discovered in 1992, scientists have found a whopping 800 planets! In order to find these foreign worlds, astronomers have developed a number of techniques to identify them. Here is an overview of the methods scientists use to find new planets.

Direct Imaging
Perhaps the easiest (and most obvious) way to find a new planet is to take a direct picture of it. Using coronagraphs to block the intense glare of parent stars, telescopes can gather images of distant planets. This method is very common in identifying new worlds.

Pulsar Timing
As the name would suggest, this method is specific to planets around pulsars—small, dense remnants of exploded stars that emit radio waves as they rotate. Irregularities in the pulses’ timing can reveal planets. The first planets discovered beyond our solar system were found using pulsar timing in 1992.

The Transit Method
The transit method watches for small dips in a star’s brightness that occur when a planet crosses (or transits) the face of the star. By looking at the timing of a particular planet’s transit, scientists can calculate variations to find multiple worlds orbiting a star. This practice has been utilized by NASA’s Kepler spacecraft, which has identified more than 2,700 potential planets since it first launched in March 2009.

Radial Velocity
Also known as the Doppler method, radial velocity picks up the tiny wobbles an orbiting planet induces on its star’s motion toward or away from the Earth. This technique measures changes in the star’s light as a result of these gravitational pulls. Radial velocity has been especially effective in locating exoplanets.

Gravitational Microlensing
When a large object passes in front of a star, its gravitational field acts like a lens as it bends and magnifies the star’s light. Astronomers use this brightening and fading light—or light curve—to determine the foreground object (usually a star). Scientists then look for secondary light curves, which can be generated by orbiting planets. This method has been helpful in finding planets deep in space that do not have a parent star.

Special Relativity
Special relativity is a new technique where scientists watch for a star to brighten as an orbiting planet “tugs” it with its gravitational pull. This tug causes photons to gather as light is focused in the direction of the star’s motion.

Astrometry
This method relies upon incredibly precise tracking of a star’s movements to identify the gravitational pulls of orbiting planets. Scientists have employed this technique for decades, to varied degrees of success.

With so many ways to find new planets, it is no wonder that we have been able to identify 800 new planets since 1992. As scientists hone these techniques and technology improves, it will be exciting to see what new discoveries are made as we expand our understanding of foreign worlds.

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