The discovery of planets around other stars, known as exoplanets, relies on various observational techniques. Here are some of the primary methods used:
Radial Velocity Method: This technique detects exoplanets by measuring the tiny wobbles induced in a star's motion due to the gravitational tug of an orbiting planet. These subtle changes in the star's radial velocity (motion toward or away from Earth) can be observed through the Doppler effect in the star's spectral lines.
Transit Method: The transit method detects exoplanets by observing the slight decrease in brightness when a planet passes in front of its host star, causing a transit. By monitoring the star's light curve, astronomers can identify regular and periodic dips in brightness, indicating the presence of an orbiting planet.
Direct Imaging: This method involves directly capturing images of exoplanets. It is challenging because the light from a planet is often overwhelmed by the brightness of its host star. Direct imaging is most successful for larger planets that are located farther away from their host stars, where the contrast is more favorable.
Gravitational Microlensing: Gravitational microlensing occurs when the gravity of a foreground star bends the light of a more distant star. If a planet is orbiting the foreground star, it can produce a detectable additional distortion in the light curve during the microlensing event.
Astrometry: Astrometry involves precisely measuring the position and motion of a star. By monitoring the star's position in the sky over time, astronomers can detect the gravitational influence of an orbiting planet through slight deviations in the star's path.
Other Methods: Additional methods include studying the changes in a star's brightness caused by the planet's reflected light (known as reflected light photometry), studying the variations in timing of pulsars, and searching for the effects of a planet's gravitational influence on a binary star system.
These methods are often complementary, and astronomers employ a combination of techniques to detect and characterize exoplanets. The discoveries of thousands of exoplanets to date have greatly expanded our understanding of planetary systems beyond our own and have opened up exciting avenues of research in the field of exoplanet science.