Astronomers detected a planet outside our Solar System orbiting a star like our Sun, for the first time in 1995. Known as ‘exoplanets’, the theoretical understanding of the formation of stars had long pointed to the existence of such worlds. Before 1995, astronomers had claimed to discover exoplanets, but it was difficult to confirm these discoveries. Later, it turned out that one such claim, made in 1988, was indeed correct. However, the discoverers of the exoplanet in 1995, Michel Mayor and Didier Queloz received the Nobel Prize in Physics in 2019.
In 2009, NASA launched a space-based telescope dedicated to finding exoplanets. It was called Kepler, in memory of the 17th-century astronomer Johannes Kepler, who discovered the laws of planetary motion. Thanks to this telescope, the number of discovered planets has gone up significantly over the years. Today, it numbers more than 4300. Astronomers have found planets with considerable diversity in sizes and kinds –– from rocky Earth-like planets to gas giants like Jupiter to icy worlds. In 2012, they found evidence that our galaxy the Milky Way harbours more planets than it has stars.
The pursuit of planets has thrown astronomers one surprise after another. They have found planets that orbit two stars simultaneously, those that orbit dead stars, and recently, even those that move around aimlessly without any parent star to go around. A question has always plagued them: How many planets like our Earth are there in the Milky Way?
A recent estimate by astronomers has ended up surprising themselves, being much more than they thought earlier. The astronomers conclude that the Milky Way could be home to about 300 million Earth-like planets: rocky, with just enough water to harbour life. The nearest one could be as close as 20 light-years, the distance travelled by light in 20 years. On astronomical scales, that’s nothing –– the radius of our galaxy is more than 50,000 light-years.
The estimate raises the possibility of the Milky Way teeming with life, we just haven’t found the other beings yet. Even if aliens do exist next door in our galactic neighbourhood, it will take at least 20 years for one-way communication between the aliens and us. Whether the Kepler’s discovery ramps up humanity’s space adventures –– remain to be seen.