Exoplanets are extraterrestrial planets that orbit a planet other than the sun. They are very difficult to see with naked eyes. A total no of 4000 exoplanets has been found till now using a wide range of methods with the help of ground-based and space-based telescopes. Astronomers have been hunting exoplanets for more than a decade now with its first noted observation dating back to 1917, with its first confirmation in 1992.

There are a number of methods used by the scientists to observe and detect the exoplanets. Let us discuss about them in a bit brief-

Direct imaging method= This is the most traditional method for finding exoplanets by direct imaging. This method is comparatively very difficult and also limited in terms of application as compared to other methods. One of the key requirements of this method is that the star system has to be relatively close to Earth to make observations and the system must be far enough such that astronomers can differentiate between the glare of the stars and the exoplanet itself. Only 50 exoplanets have been found using this method till now, in a statement quoted by Astronomer Kate Follette. However, this technique is still in its developing phase and scientists are hoping that after some adjustment to this technique, it will also help in detection of exoplanets on a scale comparable to other methods.

Transit method = When a planetary body located at some particular distance from the solar system crosses its parent star in the same plane in the line of sight as seen from a telescope from Earth, it blocks out some light of the parent star and by calculating the decrease in brightness of the star, we can calculate whether the exoplanets exists or not. It can also help calculate the relative speed of the planet with respect to its parent star and with respect to the Earth. When the exoplanet passes in front of the parent star, some of the starlight enters the exoplanet and analysis of the spectrum of that light provides scientists with evidence as to which molecules are present on the surface of the star. The transient method has helped calculate the highest number of exoplanets till now.            

Gravitational Lensing method or Microlensing Method = One of the most common methods for finding the exoplanets indirectly is known as gravitational lensing method. In this method, when a planet moves in front of the line of sight of a massive star, the star bends the path of light causing the apparent position of the star to differ from the mean position. The minute dips in the light received by the telescopes can be used to measure the actual position of the planet.

Doppler Method or Wobble Method = This method is very suitable when we want to calculate the mass of the desired planetary body. In this method, the light coming from the planetary body is observed and the analysis of the spectrum of the light observed helps astronomers to calculate the mass of the body and it can also help in searching for life on other exoplanets. By simply observing the light getting reflected off the atmosphere of the exoplanets, the astronomers can look for biomarkers in the atmosphere and conclude whether the planet is suitable for the presence of organic life or not or whether or not it is habitable or inhabitable for humans. Telescopes across the world make use of this technique but two observatories whose work is notable are Keck Telescopes in Hawaii and the La Silla observatory in China.

Written by- Sukhjit Singh

He is a bachelor student at SGTB Khalsa College pursuing B.Sc. Mathematics honors third year. He often takes multiple exciting and aims to develop multiple skills from the same.

Edited by- Shweta Mittal, Team SciComm