lpetrich
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NASA Retires Kepler Space Telescope, Passes Planet-Hunting Torch | NASA
Kepler (spacecraft), Kepler and K2 Missions | NASA
Planning of it goes back to the 1990's, with the first confirmed discoveries of exoplanets, and the spacecraft was launched in 2009. It then proceeded to stare at a patch of sky between stars Vega and Deneb for the next three years. This patch was about 10d by 10d, and Kepler observed some 150,000 stars in it.
This was done to look for transits of planets, mini-eclipses caused by planets. To get an idea of how sensitive Kepler was, Kepler would have been able to see the Earth transiting the Sun, with a dip in the Sun's apparent brightness of only 1 part in 12,000. Kepler looked at a large number of stars because transits result from planets' orbits being nearly edge-on, something very improbable for most planets. For the Earth, that would be a probability of 1/215.
But the spacecraft nevertheless observed evidence of a large number of planets, including planets with equilibrium temperatures much greater than that of Mercury. Some planets are hot enough so that their daytime side's surface is an ocean of lava. Also observed are a large number of planets in between the size ranges of the Solar System's inner planets and its gas giants -- super-Earths and mini-Neptunes.
The spacecraft was kept pointing at that area of sky by some reaction wheels, wheels which turned to turn the spacecraft in the opposite direction. One of them failed in 2012, and a second one in 2013, and the spacecraft's operators had to end its primary mission. They then thought of "K2", making the spacecraft observe along the ecliptic, while using the Sun's radiation pressure to keep it pointed properly. It continued to observe until the middle of this year, when the spacecraft got very low on reaction gas. It is now gone, and NASA has ended its operation of the spacecraft.
But Kepler's observations have yielded the discovery of about 70% of the exoplanets now known to exist, and Kepler's discoveries rather strongly imply that nearly every star has planets.
Kepler (spacecraft), Kepler and K2 Missions | NASAPlanning of it goes back to the 1990's, with the first confirmed discoveries of exoplanets, and the spacecraft was launched in 2009. It then proceeded to stare at a patch of sky between stars Vega and Deneb for the next three years. This patch was about 10d by 10d, and Kepler observed some 150,000 stars in it.
This was done to look for transits of planets, mini-eclipses caused by planets. To get an idea of how sensitive Kepler was, Kepler would have been able to see the Earth transiting the Sun, with a dip in the Sun's apparent brightness of only 1 part in 12,000. Kepler looked at a large number of stars because transits result from planets' orbits being nearly edge-on, something very improbable for most planets. For the Earth, that would be a probability of 1/215.
But the spacecraft nevertheless observed evidence of a large number of planets, including planets with equilibrium temperatures much greater than that of Mercury. Some planets are hot enough so that their daytime side's surface is an ocean of lava. Also observed are a large number of planets in between the size ranges of the Solar System's inner planets and its gas giants -- super-Earths and mini-Neptunes.
The spacecraft was kept pointing at that area of sky by some reaction wheels, wheels which turned to turn the spacecraft in the opposite direction. One of them failed in 2012, and a second one in 2013, and the spacecraft's operators had to end its primary mission. They then thought of "K2", making the spacecraft observe along the ecliptic, while using the Sun's radiation pressure to keep it pointed properly. It continued to observe until the middle of this year, when the spacecraft got very low on reaction gas. It is now gone, and NASA has ended its operation of the spacecraft.
But Kepler's observations have yielded the discovery of about 70% of the exoplanets now known to exist, and Kepler's discoveries rather strongly imply that nearly every star has planets.
