NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets – nearly doubling the number of verified planets and tripling the number of stars known to have more than one planet that passes in front of it.

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," NASA scientist Doug Hudgins said in a news release Thursday.

"Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits."

The newly discovered planets vary in size, ranging from 1.5 times the radius of Earth to larger than Jupiter, with 15 being between Earth and Neptune in size.

They orbit their host star once every six to 143 days and all are closer to their host star than Venus is to our sun.

Further observations will determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune.

The Kepler space telescope, which orbits the sun between Earth and Mars, has been searching 156,000 stars in its field of view — about 1/400th of the sky — for signs of planets since September 2009.

Kepler searches for planets by measuring tiny decreases in the brightness of stars caused by planets crossing in front of them. A planet is considered "confirmed" after the telescope has witnessed the same crossing or "transit" three times.