Kepler is a NASA mission, launched in 2009, to detect Earth-sized exoplanets. The spacecraft orbits the Sun once every 373 days, trailing slightly behind the Earth. Kepler is designed to study a region of the Milky Way, to discover exoplanets in or near their habitable zones. It also estimates the number of stars in the Milky Way which have planets.
Some facts about the telescope:
- Observatory location: In orbit around the Sun
- Mass: 1,052 kg
- Mirror diameter: 0.95 metres
- Launch date: 7th March 2009
Kepler's main scientific instrument is a photometer, which monitors the brightness of over 145,000 main sequence stars. Scientists use the transit method to detect exoplanets around these stars, by measuring dips in the brightness when the planet passes in front of the star. On 6th January 2015, NASA announced Kepler's discovery of the 1000th confirmed exoplanet.
In 2012, 3 years into the mission, one of Kepler's steering devices stopped working. A second device broke in 2013, which meant that Kepler could not continue with its primary mission. NASA announced K2, an extension to the Kepler mission which could continue despite the broken steering devices. K2 studies habitable planets around smaller, dimmer stars, and the mission is expected to continue until 2018.
As of January 2015, the Kepler mission and its follow-up observations have detected 2,300 confirmed exoplanets, which includes:
- Jupiter-sized planets very close to their star
- large Earth-like planets
- systems where a planet orbits two stars (a binary star)
- planets within the habitable zone of their star
The K2 mission extension has, as of mid-2017, discovered 143 confirmed exoplanets. These are mostly small rocky planets and gas giants.