NASA/JPL-Caltech

NASA's Kepler spacecraft has been in hot pursuit of extraterrestrial life for four years now. And, on Thursday, it's letting people know just what it's found lurking in the Milky Way.

NASA is holding a Kepler briefing at 11 a.m. PT on Thursday. It will be broadcast live on NASA Television and on UStream. The agency will also host a moderated Web chat with Kepler Deputy Project Scientist Nick Gautier of NASA's Jet Propulsion Lab. During the briefing, people can submit questions to the Kepler scientists via Twitter with the hashtag #AskNASA.

Kepler launched in March 2009 and was NASA's first mission capable of finding Earth-size and smaller planets encircling other stars within the Milky Way galaxy. The space telescope has specifically been looking for planets within a certain distance of a star that would allow for a surface temperature where liquid water could exist.

"The centuries-old quest for other worlds like our Earth has been rejuvenated by the intense excitement and popular interest surrounding the discovery of hundreds of planets orbiting other stars," NASA says in the Kepler section of its Web site. "The challenge now is to find terrestrial planets."

To date, Kepler has flagged more than 2,700 possible planets, 105 of which have been confirmed. It was not that long ago when NASA announced Kepler found its first two confirmed Earth-size planets in 2011 -- this was a major milestone in finding out how commonplace, or rare, Earth-like worlds may be throughout the universe.

It's not yet known what NASA will announce on Thursday, but given the amount of attention the agency is giving to the briefing, there will most likely be some sort of exciting news.

Below is an image showing the Milky Way region of the sky where Kepler has been searching for other planets: