NASA to hold alien planet briefing

Earth-like planets outside the solar system will help humanity know its place in the galaxy, the U.S. space agency said ahead of an alien-planet news briefing. NASA\'s alien, or extrasolar, planet announcement, set for 1 p.m. EST Tuesday, was expected to be based on findings made by the space agency\'s Kepler planet-hunting observatory, orbiting Earth since March 2009. The Kepler mission is designed to discover Earth-like planets in or near the \"habitable zone,\" where liquid water can exist on the surface of an orbiting planet, and determine how many of the billions of stars in our galaxy have such planets, NASA said. The spacecraft was named in honor of German astronomer Johannes Kepler, a key figure in the 17th century scientific revolution -- in which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science. The Kepler mission has already found 2,326 potential Earth-like extrasolar planets in the past 19 months, the National Aeronautics and Space Administration said. Twenty-eight of those were confirmed as planets, Space.com reported. Earth-like planets are rocky planets, as compared with gas giants that might not have solid surfaces. Within the solar system that Earth is part of, the rocky planets are the smaller inner planets closest to the sun. The Kepler science team announced Dec. 5 it discovered Kepler-22b, the first potentially habitable alien planet. This distant world, located about 600 light-years from Earth, orbits its sun in the habitable zone that could support liquid water and perhaps life, NASA said.