NASA\'s Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets, the U.S. space agency announced Thursday in a statement. These discoveries nearly double the number of verified planets and triple the number of stars known to have more than one planet that transits, or passes in front of, the star. Such systems will help astronomers better understand how planets form. The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen are between Earth and Neptune in size. Further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun. \"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky,\" said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. \"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.\" Launched in March 2009, Kepler was designed to discover Earth- size planets orbiting other stars. The spacecraft uses a huge digital camera, known as a photometer, to continuously monitor the brightness of more than 150,000 stars in its field of view as it orbits around the sun. Kepler searches for distant worlds by looking for \"transits,\" when a planet passes in front of a star, briefly causing it to dim. The amount of dimming reveals the size of the planet compared to the size of the star.