Explained | The James Webb telescope’s confirmation of its first exoplanet 

While the first exoplanets were discovered in the 1990s, James Webb is the only operating telescope that can characterise the atmospheres of Earth-sized exoplanets 

The story so far: After a spectacular first set of images last year, including those of the birthplaces and deathbeds of stars, and the cosmic waltz of galaxies, the National Aeronautics and Space Administration’s (NASA) James Webb Space Telescope (JWST), the largest and most powerful one ever launched into space, began its year by confirming an exoplanet.

The exoplanet, formally christened LHS 475 b, is almost exactly the size of the Earth, clocking in at 99% of our home planet’s diameter. NASA announced on January 11 that a team of two researchers — Kevin Stevenson and Jacob Lustig-Yaeger, both from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland— confirmed the exoplanet using the JWST.

Can life exist on planets besides our own? Are we alone in the universe? These are some of the profound questions humans have been seeking to answer for time immemorial.

Exoplanets are planets beyond our solar system. While these planets usually orbit other stars, some are free-floating and orbit the centre of the galaxy.

While the concept of these planets existed in theory and science fiction for centuries, the first discoveries of actual exoplanets or extrasolar planets took place in the 1990s. In 1992, two astronomers spotted two masses large enough to be planets, orbiting a pulsar (the dense remains of a dead star sending pulsating beams of light while rotating swiftly) about 2,000 light-years away. Then, in 1995, two researchers found the first exoplanet orbiting a sun-like star called 51 Pegasi. This exoplanet was a ‘hot Jupiter’ kind—a hot gas-rich giant orbiting close to its host star. This exoplanet was closer in orbit to its star than Mercury and our sun.

According to NASA, more than 5,000 exoplanets have been detected till date, and astronomers calculate that at least one exoplanet on average exists for every star visible in the night sky. The closest exoplanet, Proxima Centauri b, is orbiting a red dwarf star about 4.25 light-years away (one light-year equals 9.46 trillion kilometres).

So far, both ground and space telescopes, using different methods, have discovered exoplanets varying in size, mass, composition, the number of planets orbiting a star (planetary systems) or the number of stars orbited by the planet.Compositions of these exoplanets have varied from rocky (like the Earth or Venus), gas-rich (like Jupiter or Saturn), or even planets the density of styrofoam orcovered in molten seas of lava. Exoplanets tend to have similar elements to planets in our solar system but with varying ratios. For instance, some might have more water or more carbon.