Astronomers have found two planets "that are the closest thing ever found to Earth" and exist in its solar system's so-called "habitable zone."
The five planet system is 1,000 light years away according to University of Notre Dame astrophysicst Justin Crepp, who published a paper about his discovery in the journal Science Thursday.
"There are five small planets and two of them are in the habitable zone – this Goldilocks region where the temperature on the planet could be not too hot and not too cold but just right for water to exist in a liquid phase," Crepp says. "These two planets are the closest thing we've ever found to an Earth. They could resemble the Earth. We don't know if they have water, but they have the conditions to support water."
The potentially habitable planets were discovered by NASA's Kepler Space Telescope, which monitors stars and looks for the shadows cast on a star by planets orbiting it. The star system is known as Kepler-62, the planets are being called 'e' and 'f.'
According to Crepp, the planets' sizes, which are just slightly larger than Earth (1.41 and 1.61 Earth radii, respectively), suggest they are rocky and not made of gas. Crepp says the planets' star is slightly smaller than the sun.
"As far as we understand, anything below 3 Earth radii is almost certainly a rock, anything above that is either a mix of rock and gas or a gas giant," he says. Since its launch in March, 2009, Kepler has discovered dozens of potentially habitable planets. The telescope constantly monitors 150,000 star sequences, looking for shadows on the stars. Earlier this year, it discovered a potentially habitable planet just 6.5 light years from Earth, and last year it found one just 12 light years away.