The Kepler space telescope is the most successful planet-finding instrument ever built. On Tuesday, it chalked up its 1,000th confirmed planet discovery and one of those, Kepler 438b, was named the most Earth-like planet yet found.
It was crowned because it is only 12% larger than our world and orbits a star that gives it 40% more illumination, but it will not hold the title for long – and sooner or later Earth’s twin will be discovered.
The previous “most Earth-like world” was Kepler 186f, announced in April 2014. At the time it was described in the journal Science as “a landmark on the road to discovering habitable planets”. In this context, habitable planet means Earth’s twin: a planet that resembles ours in size and orbits a star similar to the sun, taking approximately a year to complete an orbit. Since we know that this combination led to life on Earth, most astronomers would feel comfortable labelling such a planet as habitable, though not necessarily inhabited.
Kepler 438b fails to qualify as Earth’s twin because it orbits a star smaller than the sun.
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