Exoplanets are planets that orbit a star other than our sun. The prefix “Exo” comes from the Greek and means outside; these worlds are far, far outside our own solar system. For long they have existed only in fiction and theory. It was thought it is impossible to detect planets light-years away since the relatively tiny worlds would appear billions of times fainter than their parent stars. But with the advent of newer technology and some scientist who were ready to take risks the searches for exoplanets began in the 90s and thereafter the pace of discoveries has been excessively fast. In 1992 astronomers reported the first planet-size masses around a dead star, the pulsar PSR1257+12, which sits 2,000 light-years away. Three years later came news of the first known exoplanet, a Jupiter-like gas giant orbiting its star closer than Mercury circles our sun. That world was detected around the sunlike star 51 Pegasi, a mere 50 light-years from Earth. As of 2020, more than 4000 exoplanets have been discovered and the number of known exoplanets has doubled every 27months. Looking for exoplanets directly into a planet seems implausible because of the luminosity of the parent star. The star is so bright makes it impossible to look for the planet directly. It is like observing an ant on a glowing bulb. A Jupiter-like planet would make a dip of 1%, i.e. blocks 1% of the light coming from its parent star. Also, the distance between the planet and the star also affects the fraction of light getting obstructed by the planet. In the visible range, it is impossible to observe any planet. Also, the planet must be located near the Earth and should be far away from its star in order to distinguish light from the planet and glare of its star. Thus it has many limitations, capable of holding back many discoveries. Almost 10-30 planets have been discovered using Direct imaging out of 4000 discovered.
There are two ways to observe exoplanets, direct, and indirect further there are two ways to indirectly observe exoplanets namely, Doppler and Transit. The Doppler method is a good method for discovering exoplanets. It uses the Doppler effect to analyze the motion and properties of the star and planet. Both the planet and the star are orbiting a common center of mass. This means that the star and the planet gravitationally attract one another, causing them to orbit around a point of mass central to both bodies. It is so because planets don’t revolve around its star rather the center of mass of the binary (planet-star). The transit method, another popular technique, looks for periodic dips in a star’s brightness as an orbiting planet passes in front of—or transits—its star, as seen from Earth. By measuring the amount and frequency of a star’s dimming, astronomers can estimate the orbits and masses of its planets. Additionally, researchers can calculate a planet’s surface temperature from the world’s orbital period and its star’s temperature. Another efficient method is that of Gravitational microlensing, it occurs when one star passes directly in front of a background star, as seen from Earth. The gravitational field of the foreground star acts like a lens, magnifying the light of the background star. If the “lens” star has an orbiting planet, the extra mass amplifies the magnification in a telltale way. AI has become a wonderful partner in finding exoplanets, miraculously confirming 50 exoplanets by sifting through the old data sets that too in the first attempt. With the advent of technology, things have certainly become easier and efficient. The search for exoplanets also helps satisfy the quest for Earth-like planet that could sustain life thus relieving earth from the burden and improving living standards.