A world like our own
What happened: First discovery of an Earth-sized world in a habitable zone When it happened: April 2014
Arguably Kepler’s most important and publicised discovery came in April 2014 with the announcement of Kepler-186f. This was the first Earth-sized world ever found in the habitable zone of another star, and raised the tantalising prospect that there could be other worlds like ours elsewhere in the galaxy, and possibly even life.
This planet was just 1.2-times the size of Earth, and was at a distance from its star where liquid water could exist. While the mass of the planet located about 500 light years away remained uncertain, best estimates suggested that a planet of this size was likely to be rocky. The only thing preventing this being heralded as a true ‘Earth 2.0’ was that it orbited a red dwarf star, one that was considerably dimmer than our own Sun.
While these are the most numerous stars in the galaxy they are prone to bursts of radiation, and Kepler-186f’s relative proximity to its star (40 per cent that of Earth’s orbit) raised questions about its habitability. It remains a key discovery in the history of exoplanet science, though, proving that there were other worlds like ours out there. Now we just had to find one orbiting a star like our Sun – and scientists wouldn’t have to wait long…
Kepler-186f bore many similarities to our home planet