WASHINGTON -- NASA's planet-hunting telescope has discovered two that seem like ideal places for some sort of life to flourish. They are the right size and in just the right place near their star.
The distant duo are the best candidates for habitable planets astronomers have found so far, said William Borucki, the chief scientist for NASA's Kepler telescope.
The discoveries, published online yesterday in the journal Science, mark a milestone in the search for planets where life could exist.
In the past, when astronomers found exoplanets -- planets outside our solar system -- they haven't fit all the criteria to make them right for life. Many aren't in the habitable zone, where it's not too hot and not too cold for liquid water, and until now, the handful of planets found in that ideal zone were just too big. Those are likely to be gas balls like Neptune, not suitable for life.
Similarly, the Earth-size planets that had been found up to now weren't in the right place near their stars, Borucki said.
In the game of looking for other planets like ours, the new discoveries, called Kepler-62e and Kepler-62f, are just right. And they are fraternal twins. They circle the same star, an orange dwarf, and are next to each other, closer together than Earth and its neighbor Mars.
They are slightly wider than Earth, but not too big. Kepler-62e is a bit toasty, like a Hawaiian world and Kepler-62f is a bit nippy, more Alaskan, Borucki said.
The planets circle a star that is 7 billion years old, about 2.5 billion years older than our sun.
"If there's life at all on those planets, it must be very advanced," said Borucki.