Taken from Wikipedia, "Kepler is a space observatory launched by NASA to discover Earth-size planets orbiting other stars.[5][6] Named after astronomer Johannes Kepler,[7] the spacecraft was launched on March 7, 2009,
into an Earth-trailing heliocentric orbit. The principal investigator was William J. Borucki.
Designed to survey a portion of our region of the Milky Way to discover Earth-size exoplanets in or near habitable zones and estimate how many of the billions of stars in the Milky Way have such planets,[5][9][10] Kepler's sole scientific instrument is a photometer that continually monitors the brightness of approx 150,000 main sequence stars in a fixed field of view.[11] These data are transmitted to Earth, then analyzed to detect periodic dimming caused by exoplanets that cross in front of their host star.
Kepler is part of NASA's Discovery Program of relatively low-cost, focused primary science missions. The telescope's construction and initial operation were managed by NASA's Jet Propulsion Laboratory, with Ball Aerospace responsible for developing the Kepler flight system. The Ames Research Center is responsible for the ground system development, mission operations since December 2009, and scientific data analysis. The initial planned lifetime was 3.5 years,[12] but greater-than-expected noise in the data, from both the stars and the spacecraft, meant additional time was needed to fulfill all mission goals. Initially, in 2012, the mission was expected to be extended until 2016,[13] but on July 14, 2012, one of the spacecraft's four reaction wheels used for pointing the spacecraft stopped turning, and completing the mission would only be possible if all other reaction wheels remained reliable.[14] Then, on May 11, 2013, a second reaction wheel failed, disabling the collection of science data[15] and threatening the continuation of the mission.[16]
On August 15, 2013, NASA announced that they had given up trying to fix the two failed reaction wheels. This meant the current mission needed to be modified, but it did not necessarily mean the end of planet hunting. NASA had asked the space science community to propose alternative mission plans "potentially including an exoplanet search, using the remaining two good reaction wheels and thrusters".[17][18][19][20] On November 18, 2013, the K2 "Second Light" proposal was reported. This would include utilizing the disabled Kepler in a way that could detect habitable planets around smaller, dimmer red dwarfs.[21][22][23][24] On May 16, 2014, NASA announced the approval of the K2 extension.[25]
As of January 2015, Kepler and its follow-up observations had found 1,013 confirmed exoplanets in about 440 star systems, along with a further 3,199 unconfirmed planet candidates.
[26][27] Four planets have been confirmed through Kepler's K2 mission.[28] In November 2013, astronomers estimated, based on Kepler space mission data, that there could be as many as 40 billion rocky, Earth-size exoplanets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way.[29][30][31] It is estimated that 11 billion of these planets may be orbiting Sun-like stars.[32] The nearest such planet may be 3.7 parsecs (12 ly) away, according to the scientists.
On January 6, 2015, NASA announced the 1,000th confirmed exoplanet discovered by the Kepler Space Telescope. Four of the newly confirmed exoplanets were found to orbit within habitable zones of their related stars: three of the four, Kepler-438b, Kepler-442b and Kepler-452b, are almost Earth-size and likely rocky; the fourth, Kepler-440b, is a super-Earth.[33] On May 10, 2016, NASA verified 1,284 new exoplanets found by Kepler, the single largest finding of planets to date.
Since 1988, over 3,000 exoplanets have been confirmed by all detection methods, including the Kepler mission. As of 1 August 2018, there are 3,815 confirmed planets in 2,853 systems, with 633 systems having more than one planet."