Kepler (spacecraft)
Kepler is a space telescope of NASA, which was launched in March 2009 to search for extrasolar planets ( exoplanets ). The project was named after the German astronomer Johannes Kepler, who first recognized the laws of planetary orbits.
Mid- May 2013, NASA declared that Kepler can no longer be aligned with the existing precision due to two broken reaction wheels. On 15 August 2013, the main mission has been set, it is now looking for new uses of the telescope.
The planned mission
The telescope observed a fixed cut of the sky with about 190,000 stars in the constellation Cygnus, to discover extrasolar planets. Specific objective of the project was relatively small planets (like the Earth or smaller) and thus potentially habitable ( " habitable " ) extrasolar planet to be discovered. At the same time, it provided basic data on variable stars in order to draw conclusions about the processes occurring inside can. The mission of Kepler was scheduled first for three and a half years. In November 2012, it was originally to be extended by up to four years.
Observed planetary candidates
- Total: 2740
- Size of Earth: 351
- Super -Earths: 816 (5 of earth or super-Earths in the habitable zone )
- Neptune Size: 1290
- Jupiter Size: 202
- Larger than Jupiter: 81
As of January 7, 2013
Orbit
In order to carry out the observations as undisturbed as possible, the telescope was not brought into orbit around the Earth. Kepler is located instead in a solar orbit, its orbital period ( 372.5 days ) and eccentricity vary slightly from the earth. The probe runs it behind the Earth and away over the years more and more of this. Thus it was possible to monitor the monitoring area without periodic concealment through the earth, and with minimal interference.
Technical Description
With a photometer the 1039 kg heavy and almost five feet high Telescope measured the brightness of stars to determine brightness fluctuations that indicate the passage of a planet between the star and the Space Telescope.
The optics of the Kepler photometer is designed as a Schmidt telescope. The diameter of the Schmidt plate is 0.95 m and the primary mirror 1.4 m. The focus is an array of 42 CCD sensors that could in about a palm held at arm, monitor a field of 105 square degrees, which corresponds to. Each CCD sensor has a size of 50 mm × 25 mm with a resolution of 2200 × 1024 pixels, so that the camera has a total of 95 megapixels. To increase the photometric accuracy of the optics was slightly defocused, an additional band-pass for wavelengths of 430-890 nm is installed.
The transfer of the data to the ground station is in the Ka band with up to 4.33125 Mbps. The X-band with 7.8125 bps to 2 kbps for the uplink and 10 bps to 16 kbps is still used for the downlink to control the satellites.
Search for Earth-like planets
In a passage of an extrasolar planet in Earth's size at the Space Telescope darkening of the order of 0.1 ‰ was expected ( for earth and sun 0.084 ‰). This is done at a central passage in front of the image of the star for a period of about half a day ( for the earth and sun 13 hours). Is not central of the passage, then the time of darkening is shorter. When the same change in brightness nor repeated twice at this star, while the two intervals as well as other causes of signal ( such as double stars) were the same could be excluded, a planet was adopted at a fixed orbit as a cause and was considered detected. From the thus determined orbital period and the change in brightness and size of the orbit of the planet can be determined according to Kepler's laws. Due to the distance determined in accordance with the exoplanets to its sun and the luminosity of the sun (determined by luminosity class and spectral type ) can be calculated approximately the temperature on the planet and thus its potential habitability. Due to the different orbital inclinations of the planets against our line of sight, however, occurs only in a fraction of Earth-like planet on an observable from our direction cover. The probability that such transit is observable from Earth just so results, as the ratio of star and planet orbital radius, in the case of the Earth and Sun 0.465 %.
Course
The launch of the 600 million U.S. dollars expensive telescope was made on March 7, 2009 at 3:49:57 UTC as the payload of a Delta II 7925 -10L rocket from Launch Complex 17B of the Cape Canaveral AFS. It was the 339th launch of a Delta rocket. After extensive testing and calibration of the sensors, the telescope took two months later, on his work.
In January 2010, the first five planets discovered by Kepler ( Kepler -7 Kepler -4b through 8b, see a Kepler -6 ) were announced. Kepler 1b to 3b had been discovered before the start of the probe with terrestrial observation methods. In all there are planets orbiting their stars at distances of less than 0.1 astronomical units and which have a significantly higher surface temperature than any planet in our solar system. In June 2010, the data published by 306 of the 706 previously identified Exoplanetenkandidaten. The discovery of transits cooler, potentially erdähnlicherer planet takes account of their longer orbital period a longer observation period to complete and was expected for a later phase of the Kepler mission.
In January 2011 it was announced that Kepler has discovered the hitherto smallest known rocky planet outside our solar system: Kepler - 10b. He was tracked down by observations from May 2009 to January 2010. Kepler - 10b has 4.6 times the mass and 1.4 times the size of Earth and orbits its host star every 0.84 days. He is this about 20 times closer than Mercury to the sun. Later, with Kepler - 37b, the smallest known rocky planet discovered even smaller than Mercury and only slightly larger than the Earth's moon.
On 2 February 2011, announced by NASA that 1235 planet candidates have been identified since the beginning of mission. These, five are nearly as large as the Earth and in the habitable zone. 54 habitable area and 68 in the planet Earth-sized approximately candidates are detected. As a further planet candidates have been 288 super-Earths, 662 Neptune in size, determined in 165 of the size of Jupiter and 19 larger than Jupiter.
On 5 December 2011, NASA confirmed the first planet in the habitable zone of a sun-like star. Kepler - 22b is the first of the 54 published on February 2, candidates within the habitable zone, which could be officially confirmed. To this end, Kepler must have observed in front of its star at least three passages. Furthermore announced by NASA that the number of planet candidates increased to 2326, of which 207 are about as big as Earth. Further, to date, 680 " super-Earths ", 1181 of Neptune, 203 Jupiter-like planets and 55, which are larger than Jupiter, observed.
In July 2012, the only redundant of the four reaction wheels that control the position of the telescope in space and stabilize fell out. In early January 2013, showed increased friction values on another reaction wheel, the failure of which could not have been more bearable. Then Kepler was transferred on 17 January 2013 as a planned period of ten days in a security mode ( "wheel rest safe mode" ), in the hope that the lubricant will spread by diffusion back into the stationary bearings. The reopening took place as planned and without problems between the 27th and the 29th of January 2013.
On May 16, 2013 problems were reported with another reaction wheel. Expected Kepler needs to move into a worse stabilized mode, but can continue to collect data.
On August 15, 2013, NASA said in a press statement, the final adjustment of the original Kepler mission. However, a study was commissioned, designed to evaluate the scientific operation with the two remaining reaction wheels in combination with the height control nozzles.
On November 25, 2013, NASA is known to have found a way to make the telescope despite the failure of the two reaction wheels for use again. Here are the two remaining engines work against the pressure of the photons of the sun and thus stabilize Kepler. At present, this method is tested.
On February 26, 2014, NASA announced that it managed to researchers due to improved methods of analysis to find out the old data 715 new planets. Some of them will even be located in the so-called " habitable zone ".
List of important discoveries
( not yet confirmed by other observations )