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There could be two Earth-like planets within cosmic spitting distance of our own. Both are likely too close to their star to host life, but the discovery opens the possibility of other planets in the system with more temperate climates.

Alpha Centauri is a binary star system just 4.3 light years away from our own. In 2012 astronomers announced that the system had a planet, which they dubbed Alpha Centauri Bb as it was apparently orbiting the smaller of the stars, Alpha Centauri B.

The team said it was a rocky world slightly more massive than Earth. But in 2013, other researchers called into question the existence of Bb, saying the evidence wasn't good enough.

"If you ask anyone working in exoplanets, they would all have a different opinion about the existence of Alpha Centauri Bb," says Brice-Oliver Demory of the University of Cambridge.

That's why he and his colleagues have been using the Hubble Space Telescope to search for planet. They weren't able to find it, but have instead seen hints of a second Earth-sized world in the system.

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