Scientists have identified eight new exoplanets, including one described as perhaps the "most Earth-like alien world." The far-away planets were spied by NASA's Kepler telescope, which has now identified more than 1,000 exoplanets since launching in 2009. Of the eight newly confirmed planets, three are within the so-called "habitable zone" that could hold water. Likely the most Earth-like, known as 438b, is only 12 percent larger than Earth and closer to our home planet's temperature. It replaces 186f, discovered last year, as the closest Earth twin yet.

"These are the planets we’re looking for."

According to NASA, 438b is 475 light-years away from Earth and orbits its star every 35.2 days. Another planet within the habitable zone, 442b, is 1,100 light-years away and orbits its star every 112 days. Both are likely rocky, like Earth.

NASA also announced 554 new planet candidates, raising its total to 4,175. More analysis will be needed to determine how many of these are actual planets, and how many may be Earth-like, but the discoveries are encouraging.

"Kepler collected data for four years — long enough that we can now tease out the Earth-size candidates in one Earth-year orbits," says Fergal Mullally, a scientist at the SETI Institute Kepler who led the analysis of the planet candidates. "We’re closer than we’ve ever been to finding Earth twins around other sun-like stars. These are the planets we’re looking for."