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Kepler Mission NASA Designed to find planets orbiting other stars Space telescope 。

Chinese name: Kepler space telescope
Foreign name: Kepler Mission
Alias: Kepler space telescope
Progress processing: Jet Propulsion Laboratory
system development: Bell Space Technologies
Launch time: 2009 At 22:49:57 on March 6, UTC5 time zone
Detection time: 3.5 years
NSSDC ID: 2009-011A

Organization: NASA
Quality: 1039 kg
Track type: earth Tailing Heliocentric orbit
Track height: 1AU
Orbital period: 372.5 days
Band: 400–865 nm
Caliber: 0.95m
Collecting area: 0.708 m2

catalog

sixteen recent developments
seventeen world record

Operation history

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use NASA The developed space photometer observes the luminosity of 100000 stars in the orbit around the sun, and detects whether there is the phenomenon of planetary transit ( Transit To detect planets). In order to honor the German astronomer Johannes Kepler, this mission is called Kepler Space Telescope. Kepler is NASA's low-cost discovery program focused on science. NASA's Ames Research Center is the competent authority for this mission, providing key researchers and responsible for the development of ground systems, mission implementation and analysis of scientific data.

Kepler, May 2013 Space telescope A major failure occurred in the reaction wheel of, and the telescope direction could not be set, and normal observation work was basically stopped. After several months of efforts, NASA announced on August 15 that it would give up repairing Kepler. "Kepler" ends its search outside the solar system terrestrial planet But it may still be used for other scientific research work.

In July 2018, Kepler has started the sleep mode because the fuel is about to run out, and the sleep time will last until the beginning of August 2018.^[1]

On October 30, 2018, NASA announced that the Kepler Space Telescope ran out of fuel and was officially retired.^[2-3]

Instrument Introduction

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Kepler appearance

Kepler Space Telescope（ KEPLER ）It is also translated as Kepler Space telescope It is the first time in the world to probe outside the solar system terrestrial planet 's aircraft on US Eastern Time 22:49:57:465, March 6, 2009 millisecond (11:49:57:465 ms Beijing time on the 7th), from Florida Cape Canaveral Air Base Launch pad 17-B, which will be NASA The first probe launched to detect Earth like planets. During the mission period of at least three and a half years, "Kepler" Space telescope Will compare the Cygnus and Lyra About 100000 Stellar system Conduct observation to find earth like planets and life Evidence of existence. NASA The published data shows that the photometer carried by the Kepler space telescope is equipped with a lens with a diameter of 95 cm, which will pass through the observation planet Of“ Transit ”Phenomenon searches for extrasolar terrestrial planets.

Kepler space telescope

This launch is“ Delta ”Series Carrier rocket 339th launch.

Constructional performance

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Kepler Space Telescope

1. Space spectrometer: 0.95m aperture;

Kepler space telescope

2. Main mirror: hollow structure with a diameter of 1.4m and 85%;

3、CCD Detector mirror : 95 million pixels (42 electronic couplers with 2200x1024 pixels);

4. Bandpass: peak Half width 430-890 nm;

5. Dynamic detection range: 9-16 magnitudes;

6. High quality guidance sensors: 4 Electronic coupler (CCDs) are positioned on the scientific focus plane;

7. Scientific data storage time: more than 60 days;

8. Uplink X-band: 7.8125bps － 2kbps;

9. Downlink X-band: 10bps － 16kbps;

10. Downlink Ka band: the maximum value is 4.33125Mbps;

11. Except for disposable devices, all mechanical device surfaces are covered, and the main mirror has three focusing devices;

12. Mass of flight components and assembled instruments: 1071 kg (estimated maximum);

13. Power of flight components and assembled instruments: 771W (estimated maximum)

Running track

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Running track

Kepler It is not in the orbit around the earth, but in the solar orbit following the earth, so it will not be obscured by the earth and can be observed continuously, Photometer Will not be affected by Diffuse light influence. Such an orbit avoids gravity Perturbation And inherent in the Earth's orbit torque There can be a more stable observation platform. The photometer points to Cygnus and Lyra The field is far away from Ecliptic plane Therefore, in the orbit around the sun, sunlight will not leak into the photometer. Cygnus will not be taken by Cooper or Asteroid belt It is a good choice for observation because of the obscuration of 30% of the celestial bodies.

Another advantage of this choice is that the direction Kepler points is that the solar system is around Galaxy The center of motion, so the distance between the stars observed by Kepler and the center of the Milky Way is roughly the same as that of the solar system, and they are also close to the plane of the Milky Way. This is an important fact. If there are galaxies Habitable zone As suggested Earth Difference Hypothesis 。

Mission purpose

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Kepler^[4] Detector plan yes Galaxy More than 100000 stars are detected in the hope of finding those that can support the existence of life terrestrial planet 。

1、 Determination of diversity Spectral type Number of terrestrial planets and large planets in or around habitable regions of stars

Aliens in Kepler Space Telescope

This planetary measurement data is derived from the number and size of planets, as well as the number and spectral type of stars monitored. Even if the Kepler detector finds that the data is zero, it is also of great scientific significance. After all, it has confirmed that more fixed star The system has been searched and surveyed. Excluded the possibility of habitability planet Possibility.

2、 Determine the distribution of planets with different sizes and the semi major axes of planets

The determination of the distribution of planets of different sizes and volumes is mainly derived from the observation of the decline of the faint brightness of the planet and the characteristics of the star system where the planet is located.

be based on Kepler's third law By measuring the mass and periodic age characteristics of stars, we can further determine the corresponding data of the semi major axis of the planet. It is reported that the content of Kepler's third law is: the farther the planet is from the sun, the weaker the force on the planet, and the acceleration of the planet decreases, so the slower the planet moves, the Revolution period The longer. planet The semi major axis can also pass through the ground Spectroscope and fixed star According to the observation results of the model, the uncertainty factor of determining the semi major axis of the planet is related to the center of the star system Stellar mass of

3、 Evaluating the number of planets and the orbital distribution of planets in a multi star system

This assessment can be compared with those found in one to many star systems Planetary system If the multi star system is closely combined, or can be realized by Angular resolution This kind of multi star system can be observed by spectroscope instrument on the ground.

4、 Determination of density, mass, volume, albedo and semi major axis of short period giant planets

Short period giant planets can be detected by their reflected light changes. Similarly, their semi major axis determination is also derived from the use of Kepler's third law Determine the mass and periodic age characteristics of stars.

Transit The number of planetary transits accounts for 10% of the measured number of planets of a certain size. In the solar system, transits are Inner planet An astronomical phenomenon that passes between the sun and the earth and partially blocks the solar surface. If one of the two inner planets happens to pass between the earth and the sun, the observer on the earth will see a black spot passing through the sun's circle, which takes more than an hour. People call this phenomenon transit. For a star outside the solar system, transit refers to the astronomical phenomenon that the planet of the star passes through the line between the star and the Earth, and partially obscures the star for Earth observers.

According to the detection plan, Kepler detector In the first few months of the exploration mission, a certain number of short period giant planets will be found, and the size and semi major axis of these planets will be measured. Their albedo will be determined by measuring the modulation amplitude of reflected light. The density of the planets is determined by the Kepler detector Spectroscope And the planet appears Transit phenomenon This method was used to determine the density of HD209458b planet.

5、 Using the complementary technology, measure each photometric angle to identify the Planetary system Number of additional planets in

Use space Interferometer (SIM) and ground Doppler spectroscope to search for super massive planets without transit, and further provide detailed information of each detected planetary system.

6、 Detection has Planetary system Properties and characteristics of the stars of

Scientists use ground observation instruments to detect the spectral type, luminosity level and metallicity of each star. In addition, there are star rotation ratio, surface brightness heterogeneity, and stellar activity directly obtained from photometer data. use Kepler detector Measurement by seismoseismology and other instruments fixed star Age and quality.

Future exploration missions

Based on the survey and analysis results of Kepler detector, the future space interferometer (SIM) and“ terrestrial planet The "Searcher" (TPF) probe will conduct more in-depth exploration and discovery of Earth like planets. It is reported that the "Earth like Planet Searcher" is scheduled to launch in 2011.

stay Kepler On the basis of the detector, the following survey conditions are also required for future exploration tasks: identify and determine the common star characteristics of the main star in future planetary search projects; Determine the space volume to be searched; Provide the space interferometer (SIM) with a list of survey targets with terrestrial planetary systems.

Extraterrestrial search

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Extrasolar planets Search history

particular year	name	country	achievement
one thousand nine hundred and eighty-seven	Lik Carnegie Planet Search	U.S.A	Hundreds of exoplanets have been discovered
one thousand nine hundred and ninety	Hubble Space Telescope	U.S.A	The first planet around Beiluo Sect was discovered by direct imaging
one thousand nine hundred and ninety-three	ELODIE, SOPHIE spectrometer	France	The first planet was found around a sun like star
one thousand nine hundred and ninety-eight	Anglo Australian Exoplanet Search	UK, Australia	29 planets have been discovered by 2012
two thousand and two	Magellan telescope	Chile	As of 2010, 9 exoplanets have been found
two thousand and three	MOST	Canada	Study the atmospheric changes of planets during transit
two thousand and three	Spitzer telescope	U.S.A	Capture infrared radiation from exoplanets
two thousand and three	HARPS	Europe	About 150 exoplanets have been found orbiting sun like stars
two thousand and six	COROT	France	About 20 exoplanets have been found
two thousand and nine	Kepler telescope	U.S.A	Used to search for Earth like planets

Detection principle

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Schematic diagram of launch surface tracking of Delta 2 carrier rocket

Kepler is a Space telescope , designed to detect distant fixed star To determine terrestrial planet How universal it is. Kepler will use“ Transit method ”Indirect detection of planets. In addition to revealing the existence of a planet, this light signal can also tell us the volume and orbit of the planet. After that, scientists will use other measurement methods to determine whether each planet found is located in an area suitable for life, or measure the distance between the planet and its surrounding star to determine whether there is liquid water on its surface.

The principle of planet detection is that when the planets in the star system move between Kepler and the stars, due to the shelter of the planets, Kepler photometer sensor receives Stellar brightness Will become weaker. Scientists on the ground can calculate the size and orbital period of planets according to the periodic weak change of star brightness. Kepler telescope The weak change in brightness that can be detected can be as small as about 10 parts per million. This technique has been used by scientists for about ten years, and has helped astronomers find more than 300 large planets. The Kepler telescope targets smaller planet , habitable planets as big as the earth, all around their mother fixed star work.

Detection mode

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“ Transit ”It refers to the phenomenon that a planet passes in front of its parent star in the view of observers. For example, it can be observed on the earth Mercury transit or Venus transit At this time, people saw that there seemed to be a small black spot slowly moving on the surface of the sun. Similarly, observe others fixed star The system will also see Transit phenomenon "Kepler" is calculated through relevant observation data planet Characteristics of.

Kepler can measure the Revolution period According to this, the orbital size of the planet can be roughly calculated; Kepler can also observe transit depth（ Stellar brightness And calculate the size of the planet. For the parent star of a planet, its mass can be estimated according to its spectrum, luminosity and other parameters. Combining these data, we can speculate whether a planet is suitable for life.

The target area observed by Kepler is located in Galaxy Cygnus and Lyra Since the observation in this direction is less affected by the sun and other celestial bodies, it is conducive to continuous observation. In addition, there are many stars and appendages in this region planet 。

Task Details

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Kepler space telescope

Kepler It is not in the orbit around the earth, but in the solar orbit following the earth, so it will not be obscured by the earth and can be observed continuously, Photometer Will not be affected by diffuse Light effects. Such an orbit avoids gravity Perturbation And inherent in the Earth's orbit torque , can have a more stable observation Platform. The photometer points to Cygnus and Lyra The field is far away from Ecliptic So in the orbit around the sun, the sun will not leak into the photometer. Cygnus will not be taken by Cooper or Asteroid belt It is a good choice for observation because of the obscuration of 30% of the celestial bodies.

Another advantage of this choice is Kepler The direction is that the solar system Galaxy The center of motion, so the distance between the stars observed by Kepler and the center of the Milky Way is roughly the same as that of the solar system, and they are also close to the plane of the Milky Way. This is an important fact. If there are galaxies Habitable zone As suggested Earth Difference Hypothesis 。

It is estimated that the mass of the spaceship is 1039 kg and its caliber is 0.95 meters, Primary mirror (on Earth orbit The largest lens outside) 1.4m, view (FOV) has 105 deg2 (about 12 degrees in diameter), which is about the field of vision covered by a fist when the arm is straight. The photometer has a soft focus to provide good photometric measurements rather than clear images. Combined luminosity difference Accuracy （CDPP， combined differential photometric precision）， For a solar like fixed star The image synthesis for 6.5 hours is 20 ppm, including the expected 10 ppm luminosity change of the star itself. The light change caused by the transit of a planet similar to the Earth is 84 ppm, and the orbit will last at least 13 hours after passing the star center. The focal plane is composed of 42 1024 X 2200 CCD, and the size of each pixel is 27 micron Is the largest camera launched into space. This array is connected to the outside by a Thermal conduit To cool. CCD The data is read out every 3 seconds and can remain for 15 minutes. Only the data corresponding to the pixel of the interested target star will be saved and transmitted back to the ground through telemetry. It is estimated that this task will cost 600 million dollars in its life cycle, including 3.5 years of operation.

According to a recent report on NASA's website, NASA is ushering in two milestones in its search for exoplanets. First, Kepler Space Telescope, which lasted for three and a half years, successfully completed its main mission; On the other hand, this meritorious Space telescope The equipment is about to start its extended mission, which will last for 4 years.

Mission Operations

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Kepler Space Telescope Colorado Boulder Atmospheric and Space Physics Laboratory（ LASP ）Responsible for operation. Solar array When it is at the equinox every year, it will rotate to the direction facing the sun. These rotations will be used to optimize the sunlight shining on the array and make Thermal radiator Keep pointing in the direction of deep space. At the same time, LASP and Bell Space Technology Corporation, which builds spacecraft and instruments university of colorado Control center for operation. LASP carries out the basic task plan and the initial collection and distribution of scientific data.

NASA Contact the spacecraft through the X-band communication line twice a week to give instructions and update the status. Download scientific data with Ka tape once a month. The maximum transmission rate is 4.33Mb/s. Kepler The spaceship will carry out part of its own Data analysis , scientific data will be transmitted only when necessary to maintain bandwidth.

The telemetry scientific data collected by LASP during the mission will be sent to the Maryland Baltic Johns Hopkins University On campus Space telescope Kepler Institute of Technology data management Center (DMC). These telemetry scientific data will be decoded and processed into uncorrected FITS - and formatted into scientific data products by DMC, and then through the amicus The scientific operation center (SOC) of the research center conducts calibration and final processing. SOC will send back the corrected and processed data products and scientific results to DMC for long-term archiving and send them to astronomers around the world via the STScl Multi Task Archive (MAST).

Product features

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1、 Kepler telescope Is that the world is the first one to really discover terrestrial planet It will discover habitable planets orbiting stars like our sun. Water is the foundation of life, and this livable area must be fixed star An area of suitable temperature for the presence of water planet There may be pools on the surface.

2. On Kepler telescope Before the end of more than three and a half years of tasks, it will allow us to better understand other terrestrial planet In our Galaxy More or less. This will be a key step in answering a long question: Are we the only one in the universe?

3. Kepler telescope discovered Stellar brightness Detect by periodically darkening Extrasolar planets 。 When we observe the sky from a position on the earth, if a planet passes in front of its parent star, we can find that this planet will cause its parent star to dim slightly. The Kepler telescope can better understand this situation.

4、 Kepler Wangyuan has the largest camera in space, with a 95 megapixel charge coupled device (CCD) array, just like the CCD Same.

5、 Kepler telescope It is so powerful that when it observes the earth from space, it can find that people living in small towns turn off their porch lights at night.

6. Kepler Space Telescope Locates Second in the Earth Sun System Lagrange point , revolves around the sun, so the target sky area can be detected in full time.

7. Observation target away Ecliptic surface , avoidable celestial bodies The interference of concealing food.

Composition and performance

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Instrument composition and system performance

1. Space spectrometer: 0.95m aperture;

2. Main mirror: hollow structure with a diameter of 1.4m and 85%;

3. CCD detector: 95 million pixels (42 electronic couplers with 2200x1024 pixels);

Instrument composition and system performance

4. Bandpass: peak half width 430-890 nm;

5. Dynamic detection range: 9-16 magnitude stars;

6. High quality guidance Sensors: 4 electronic couplers (CCDs) are positioned on the scientific focus plane;

7. Scientific data storage time: more than 60 days;

8. Uplink X-band: 7.8125 bps － 2kbps;

9. Downlink X-band: 10 bps - 16 kbps;

10. Downlink Ka band: the maximum value is 4.33125 Mbps;

11. Except for disposable devices, all mechanical device surfaces are covered, and the main mirror has three focusing devices;

12. Mass of flight components and assembled instruments: 1071 kg (estimated maximum);

13. Power of flight components and assembled instruments: 771W (estimated maximum)

major milestone

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Kepler Space telescope yes NASA First to search around Sun like star The major milestone events of the exploration project of the Earth's large and small extrasolar planets that has been in operation so far include: the launch; Discovery of the first exoplanet; Finding exoplanets with the smallest mass and diameter; First 6 found Planetary system ； Discover the first planet orbiting two suns; Found at Livable zone The smallest planet orbiting a sun like star.^[5]

New Planet Discovered

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New Planet Discovered by Kepler

Kepler 9b and Kepler 9c

Kepler 9b and Kepler 9c ：^[6] Kepler The first series of continuous discoveries in the early period also included two planets orbiting the star Kepler-9. Kepler 9b and Kepler 9c are the first multi star galaxies in Kepler's exploration mission. These Saturn sized planets revolve around their parent stars for about 19 days and 38 days. Third Super Earth The size of the star was later confirmed to exist in the galaxy.

Kepler-10b ：

Kepler-10b

Kepler Space Telescope has been looking for the most Earth like planet. Kepler-10b is the first rock planet confirmed to be similar to our Earth. The radius of this planet is about 1.4 times that of the Earth, and the cycle around its parent star is less than one day. Kepler's ultra accurate measurement can determine that the planet's mass is 4.6 times that of the Earth, which makes it similar to an iron dumbbell in density. Considering its composition and its close proximity to the parent star, some scientists believe that Kepler-10b More like a super Mercury Not the Earth twins.

Kepler-22b ：

Kepler-22b

This planet is 600 meters from the earth Light year And its radius is 2.4 times that of the earth, and it revolves around a sun like star. In addition, its year is about 290 days, which is slightly shorter than our Earth. Scientists do not know its composition, but if it had atmosphere, it might have a huge ocean and there might be life.

Kepler-42：

Kepler-42

Kepler-42 contains the smallest solar system ever observed. Red dwarf Surrounded by three rocky planets smaller than the Earth, the smallest is about the size of Mars. All these planets have orbital periods of less than two days, which means that they are all too hot to have any life.

Volume comparison map: 22-b, 69-c, 62-e, 62-f, Earth

Kepler 22-b, 69-c, 62-e, 62-f

The size is appropriate and the location is appropriate, "the Associated Press reported on the 19th, Kepler -62 Planetary system About 1200 away from the earth Light year , on Lyra 。 In this system, five planets orbit a star that is smaller, colder and older than the sun, Kepler-62e Kepler-62f and Kepler-62f are the two outermost ones. Their volumes are 1.6 times and 1.4 times of the Earth's, respectively, and their heat radiation is only 1.2 times and 0.4 times of the Earth's, Revolution period 122 days and 267 days respectively. Scientists at the Max Planck Institute for Astronomy in Germany said that the temperature of Kepler-62e "may be like Washington in May". Researchers speculate that these two planets are mainly composed of rocks or ice. Only after obtaining the relevant atmospheric spectral characteristics can we know whether they are really "livable". "If there is life on them, it must be very advanced". Another "New Earth" Kepler -69c at Kepler-69 Planetary system , in Cygnus, about 2700 away from Earth Light year The volume is 1.7 times of the earth, the revolution period is 242 days, and the composition material is still uncertain. In addition, the other four planets in these two planetary systems Revolution period Only ten days, which means they are very hot and not suitable for human survival.

Abandonment of repair

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In May 2013, NASA, the most powerful in searching for exoplanets Kepler Space telescope In case of a major failure, the satellite basically stopped its normal observation work. If the engineers of NASA cannot repair it in time, the $600 million space project may die prematurely.

On August 19, 2013, it was reported on NASA's website that after several months of analysis and testing, NASA Kepler telescope Project team A few days ago, it was officially announced that it would give up the efforts to restore the telescope to its full working state, and instead consider what kind of scientific tasks the telescope equipment could undertake under the current adverse conditions.

Kepler telescope has completed its main scientific mission in November 2012, and immediately started its original 4-year plan extension period. Its main scientific task is to search for extrasolar planets orbiting distant stars outside the solar system. However, due to the inability to assemble three reaction wheels to maintain the normal working state of the telescope, the project team decided to analyze the large amount of data collected previously, and the engineer team would try to repair the faulty reaction wheel, while actively considering that if the repair failed, this advanced Space telescope Whether we can still undertake some other types of scientific tasks.

recent developments

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On May 15, 2013, Kepler Space telescope Due to the failure of the reaction wheel, it was unable to set the direction of the telescope, so it was forced to stop its exoplanet search mission. After the failure, scientists tried to restore the observation ability of the telescope, but the final efforts were unsuccessful. At present, only two reaction wheels can work, and the other two reaction wheels failed in 2012 and 2013, so Kepler telescope lost the accuracy of observing extrasolar stars, This not only makes NASA lose an exoplanet probe with extremely advanced observation capability, but also makes us find terrestrial planet Our pace slowed down. On August 18, 2013, NASA said that it was unable to repair and launch the K2 mission, so that the telescope could adjust its attitude on the ecliptic plane of the earth's revolution with the help of the force generated by solar photons, and still be able to continue to perform the observation mission. For the newly assigned K2 mission, scientists believe that the detector can run along the ecliptic plane, making in-depth observation of about four to five target objects every year. The so-called ecliptic plane is the orbital plane of the earth's revolution. When in this orbit, Kepler telescope can obtain stable light pressure, that is, the force generated by solar photons on the detector, This helps the detector maintain a good observation stability to compensate for the decline in pointing accuracy caused by the reaction wheel failure. However, each mission cycle is limited to 75 days, so the number of target objects observed each year can only be maintained at 4-5.

According to the NASA website, in the early morning of July 24, 2015, Beijing Time, Astronomy Scientists confirmed the discovery of the first planet (code name:“ Kepler-452b ”）This is an important milestone on the way for mankind to find another earth. The discovery of "Kepler-452b" has increased the number of confirmed exoplanets to 1030.

The "habitable zone" refers to the area where the planet is located at a suitable distance from the star. In this area, the heat transferred from the star to the planet is moderate, neither too hot nor too cold, and can maintain the existence of liquid water.

On April 6, 2016, Kepler's microlens observation will be temporarily unable to start unless engineers can make the detector restart. The telescope is now about 120 million kilometers away from the earth, which means that every round trip communication takes 13 minutes.^[7]

At 13:00 on December 14, 2017, NASA held a teleconference to unveil the "major discovery" of Kepler Astronomical Telescope for many days, and identified two newly discovered planets in Kepler 90 galaxy 2545 light-years away from the Earth - Kepler-80g and Kepler-90i, which is the first galaxy with eight planets like our solar system discovered by humans.^[8-9]

In July 2018, as the fuel was about to run out, Kepler had started the sleep mode, and the remaining fuel should first ensure the data transmission. The sleep time will last until the beginning of August, when engineers will wake it up, command it to point the airborne antenna to the earth and start to return data. If all goes well, Kepler will use the remaining fuel to carry out the final observation task after completing the data transmission.^[1]

On October 30, 2018, NASA announced that the Kepler Space Telescope has "retired". It has worked in space for more than nine years and has discovered 2662 exoplanets, many of which may be pregnant with life.^[2]

world record

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As of January 24, 2022, 3184 exoplanets have been found and confirmed according to the observation results of Kepler Space Telescope, setting the world record for the number of exoplanets found by a single telescope (Guinness World Record ）。^[10]

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