Might there be other life in the solar system? Kepler space telescope has spotted what scientist think is a Earth-sized planet in orbit around a star in the so-called Goldilocks zone.

Elisa Quintana, research scientist at the SETI Institute at NASA's Ames Research Center, said: "We know of just one planet where life exists – Earth. When we search for life outside our solar system, we focus on finding planets with characteristics that mimic that of Earth.

"Finding a habitable-zone planet comparable to Earth in size is a major step forward," she explained. "M dwarfs are the most numerous stars. The first signs of other life in the galaxy may well come from planets orbiting an M dwarf."

The planet orbits a small M-class red dwarf star around 500 light years from Earth. dubbed Kepler-186f, it is about 10 per cent larger than Earth in size and with slightly stronger gravity.



"Being in the habitable zone does not mean we know this planet is habitable. The temperature on the planet is strongly dependent on what kind of atmosphere the planet has. Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth," said Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames.

Victoria Meadows, professor of astronomy at the University of Washington, said that the planet is closer to its sun than Earth is to our star, but only receives around a third of the sunlight we do, but that that's more than enough for plant life to thrive.

"There's no good reason at the moment why M-dwarf planets could not be habitable," she said, "so we do consider them to be perfectly viable potential places for habitability. This particular planet is small, so that really increases its probability of being rocky, habitable, and able to support liquid water in oceans."