COROT (space telescope)

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COROT
COROT
Type: Research satellite
Country: EuropeEurope Europe
Operator: European space agencyESA ESA
COSPAR-ID : 2006-063A
Mission dates
Dimensions: 630 kg
Size: 4.1 m × 1.98 m × 1.98 m
Begin: December 27, 2006
Starting place: Baikonur
Launcher: Soyuz 2.1b / Fregat
Flight duration: 7.5 years
Status: Out of service
Orbit data
Orbit inclination : polar (90.0225 °)
Apogee height 893 km
Perigee height 602 km
Eccentricity : 0.0204295

COROT (acronym from French " CO nvection, RO tation et T ransits planétaires" or English "COnvection, ROtation and planetary transits"; in German "convection, rotation and transits of exoplanets") was a space telescope operated by the French space agency CNES . It tracked changes in the brightness of a large number of stars in order to derive information about their internal physical properties and looked for exoplanets using the transit method . The rocket launch was on December 27, 2006. A computer defect on November 2, 2012 put an end to Corot's observations; The mission was to be extended until 2013. On June 20, 2013 the mission was officially declared over, and on June 17, 2014 the satellite was switched off.

Mission objectives

Asteroseismology

According to the method of asteroseismology , the stars' internal structure should be deduced from regular fluctuations in brightness. For the investigations, stars of the main sequence ( spectral classes F and G, Delta-Scuti stars ) with an apparent brightness of greater than 9 mag and less than 6.5 mag were selected. An observation period in the so-called main program lasted 150 days. During this time Corot observed 10 stars at a time. The following parameters were determined through a high-precision measurement of the fluctuations in brightness (0.1 to 10 Hz):

In addition to the 150-day sections of the main program of observation, Corot had an "exploratory" program. The exploratory program examined a large number of different stars of the spectral classes B to K. For this, periods of around 20 days were inserted between the observation periods of the main program. The measurement frequency was reduced to 0.6 Hz. This made it possible to obtain statistical information about the relationship between the types of oscillation as a function of the mass , age , angular velocity and metallicity of the stars examined. 50 to 100 objects should be examined.

Exoplanet Search

By monitoring a large number of stars, one should search for exoplanets that lead to a short-term decrease in brightness during transit in front of their parent star ( transit method ). At the same time, 12,000 stars were monitored (up to 180,000 in total). The stars examined had an apparent magnitude of 12 mag down to 15.5 mag. As a rule, stars of the spectral classes K and M. In addition to the discovery of "hundreds" of Jupiter- sized planets, the mission's scientific planning documents expected that 10 to 40 earth-sized planets would be discovered in other solar systems. After all, the search for exoplanets was far less successful than planned, see Discoveries and Scientific Results .

course

COROT is a 170 million euro project by the French space agency CNES in cooperation with ESA with the participation of Austria, Belgium, Germany, Spain and Brazil. The planning began in 1994 and led through various intermediate steps in 1996 (positive decision in principle) and 1998 (decision on the definition phase) in October 2000 to the final decision to build Corot. In June 2001, CNES and ESA signed a cooperation agreement. In 2004, important individual components such as the camera were subjected to intensive tests. The assembly of Corot began in January 2006. In September of the same year, Corot passed the space flight fitness test.

The satellite was launched into polar earth orbit by a Russian Soyuz-2 / Fregat rocket from the Baikonur spaceport on December 27, 2006 at 3:23 pm CET . The telescope is oriented at a right angle to the orbital plane so that neither the earth nor the sun come into view. On the night of January 17-18, 2007, the first test recordings were successfully carried out.

Originally, the duration of the work stay in Earth orbit was planned from December 2006 to October 2010. On October 23, 2009, the CNES, together with its national ( CNRS and Observatoire de Paris) and international partners (ESA, Austria, Germany, Belgium, Brazil and Spain) decided to extend the mission to March 31, 2013.

In October 2012 the mission was extended to 2016. Due to a technical problem, the telescope stopped producing scientific data on November 2, 2012. After restarting the system in December 2012 had no effect, there was little hope of solving the problem. In March 2013, at a conference of the scientists involved in COROT, it was announced that the system error could now be reproduced. Based on the data, it was assumed that the telescope was probably not damaged. However, since the scientists were unable to put the instruments back into operation, the mission was declared over on June 20, 2013. The satellite was moved to a deeper orbit in December 2013. After some technical experiments were carried out, the satellite was switched off on June 17, 2014.

technology

COROT was based on the French PROTEUS platform for small satellites . At the start it had a mass of 630 kg. The payload accounted for 300 kg of this. The diameter of Corot is 1.98 m with a length of 4.10 m. The solar panels have a span of 9 m and deliver 530 W of energy.

COROT had a reflector telescope with a main mirror diameter of 27 cm on board. The telescope achieved a field of view of 2.8 ° × 2.8 °. The camera attached to the telescope had four CCDs . Two of the CCDs were used to search for exoplanets (E1 and E2) and two for asteroseismology (A1 and A2). E1 and A1 together form a photometric chain, A2 and E2 the second.

For the search for exoplanets , stars were monitored whose apparent magnitudes were between 12.0 mag and 15.5 mag. Their light was split into several colors with a prism in order to be able to better distinguish coverages by planets from other fluctuations in brightness. For the asteroseismological studies, the light from bright stars was defocused over a few hundred picture elements of the CCD in order to achieve better measurement accuracy.

COROT successively examined several star fields in the constellations snake and unicorn . Consequently, all “discoveries” of the system can be found there.

Discoveries and Scientific Results

Exoplanets

In total, more than 35 exoplanets have been discovered since 2007.

In April / May 2007 COROT discovered its first exoplanet. It is a gas giant called “ CoRoT-1 b ”. It has 1.3 times the mass of Jupiter and is around 1,500 light years from Earth.

On December 20, 2007, the discovery of another exoplanet was announced. The object of 3.5 times Jupiter's mass with the designation " CoRoT-2 b " accompanies a star of the spectral class K0V in the constellation Snake . The star and exoplanet are about 800 light-years away from Earth.

In 2008, CoRoT-3b was also discovered, which - due to its relatively high minimum mass of around 22 Jupiter masses - is probably a brown dwarf .

The next three exoplanets discovered are of the same order of magnitude as the gas giants in the solar system . In 2008, CoRoT-4 b and CoRoT-5 b were discovered. CoRoT-5 b is slightly larger than Jupiter, but a bit lighter with about 0.7 Jupiter masses. The orbit time of CoRoT 4 b is 9.2 days, the orbit time of CoRoT-5 b is almost exactly 4 days. CoRoT-6 b was discovered in 2009. With 1.15 Jupiter radii it is only slightly larger than Jupiter, but has 3.3 Jupiter masses. The cycle time is just under 9 days.

On February 3rd, 2009 the discovery of another planet, named " CoRoT-7b ", was announced. The Earth-like planet is about 4.8 times more massive than Earth and has a radius of about 1.75 Earth radii. Since the density is somewhat higher than that of the earth, there are strong indications that CoRoT-7b is an earth-like planet, possibly rocky ( rocky planet ). CoRoT-7 has an extremely high orbital speed of more than 700,000 km / h and orbits its central star in just 11 hours. With a mass of just 4.8 Earth's, it is the smallest exoplanet discovered to date.

On September 16, 2009 it was announced that CoRoT-7 b has a sibling planet: CoRoT-7 c . The new exoplanet is also probably a rocky planet. It has eight Earth masses, an orbital speed of 3 days and 17 hours and orbits its central star at a slightly greater distance than CoRoT-7 b. Atypical for the CoRoT mission, CoRoT-7 c was found through its gravitational effect on the central star. For the first time, CoRoT-7 b and c have clearly demonstrated two earth-like rock planets in an extraterrestrial star system.

On June 14, 2010, the discovery of six more exoplanets was confirmed. The first is CoRoT-8 b . The mass is given as about 70% of the mass of Saturn and is therefore one of the smaller exoplanets that have been found using the transit method to date . The discoverers suspect that, like Uranus or Neptune, it is a very cold gas giant .

On March 17th, 2010, CNES and its partners announced the discovery of CoRoT-9b . Corot-9b orbits its central star with a period of a good 95 days. With a closest approximation of 54 million km, the orbit is the largest orbit to date for an exoplanet found by the transit method. The temperatures are probably between –23 ° C and +157 ° C. Its diameter is comparable to that of Jupiter . Corot-9b has only 84% of the mass of Jupiter. The ESA speculated that on a moon this exoplanets liquid water could exist.

The discovery of the following five exoplanets was announced on June 14, 2010. CoRoT-10 b3 is a giant planet with a strongly eccentric orbit . Due to the sometimes very small distance to the parent star, the surface temperature can increase from 250 to 600 ° C within a few days. The orbital period is 13 days. The most remarkable thing about CoRoT-11b is that the discovery was successful at all. The parent star rotates very quickly around its own axis at 40 hours. The sun needs 26 days for this. Rapid rotation makes discovery difficult.

CoRoT-12 b, CoRoT-13 b and CoRoT14 b are giant planets that orbit their parent star at a short distance. Corot-12 b has 16 times the circumference of Jupiter and is very hot and bloated ( bloated hot Jupiter ) because of the close spacing . CoRoT-13 b , on the other hand, is smaller than Jupiter, but twice as dense. It may have a rock core. CoRoT-14 b is only the second exoplanet that is very hot and very massive at the same time. Its size is roughly the size of Jupiter. But it has 7.5 times the mass.

After all, CoRoT-15 b is a very dense brown dwarf , i.e. H. an object that stands between a star and a planet. It is only slightly larger than Jupiter, but about 60 times more massive.

star Constellation Apparent
brightness
Distance
( ly )
Spectral
class
planet Mass
( M J )
Radius
( R J )
Orbital time
( d )
Semi-axes of
the ellipse

( AU )
Orbital
eccentricity
Rail
inclination

( ° )
Discovery
(y)
CoRoT-1 Monoceros 13.6 G0 b 1.03 1.49 1.50896 0.0254 85.1 2007
CoRoT-2 Aquila 12.57 G7V b 3.31 1.465 1.743 0.0281 87.84 2007
CoRoT-3 Aquila 13.3 F3V b 21.77 1.01 4.2567994 0.057 0 85.9 2008
CoRoT-4 Monoceros 13.7 F8V b 0.72 1.19 9.20205 0.09 0 90 2008
CoRoT-5 Monoceros 14th F9V b 0.467 1.33 4.0378962 0.04947 0.09 85.83 2008
CoRoT-6 Ophiuchus 13.9 F9V b 2.96 1.166 8.886593 0.0855 0.01 89.07 2009
CoRoT-7 Monoceros 11,668 K0V b 0.0149 0.136 0.853585 0.0172 0.12 80.1 2009
c 0.04266 3,698 0.046 0.12 2009
CoRoT-8 Aquila 14.8 K1V b 0.215838656 0.569186492 6.21229 0.063 0 88.4 2010
CoRoT-9 Serpens 13.7 G3V b 0.84 0.94 95.273804 0.407 0.133 89.9 2010
CoRoT-10 Aquila 15.22 K1V b 2.75 0.97 13.2406 0.1055 0.53 88.5 2010
CoRoT-11 b Serpens 12.94 F6V b 2.33 1.43 2.994325 0.04351 0 81.41 2010
CoRoT-12 Monoceros 15.52 G2V b 0.917 1.44 2.828042 0.04016 0.07 85.48 2010
CoRoT-13 Monoceros April 15 G0V b 1.308 0.885 4.03519 0.051 0 88.02 2010
CoRoT-14 Monoceros 16.03 F9V b 7.6 1.09 1.51214 0.027 0 79.6 2010
CoRoT-15 Monoceros F7V b 63.4 1.12 3.06036 0.045 0 86.7 2010
CoRoT-16 Scutum 15.64 G5V b 0.535 1.17 5.35227 0.0618 0.33 85.01 2010
CoRoT-17 Scutum 15.46 G2V b 2.43 1.02 3.768125 0.0461 0 88.34 2010
CoRoT-18 Monoceros 14.99 G9V b 3.47 1.31 1.90007 0.0295 0.08 86.5 2011
CoRoT-19 Monoceros 14.78 F9V b 1.11 1.29 3.89713 0.0518 0.047 87.61 2011
CoRoT-20 Monoceros 14.66 G2V b 4.24 0.84 9.24285 0.0902 0.562 2011
c 17th 1675 2.9 0.6 2018
CoRoT-21 Monoceros 16 F8IV b 2.26 1.3 2.72474 0.0417 0 86.8 2011
CoRoT-22 Serpens 11.93 G0IV b 0.0383853 0.435365216 9.75598 0.092 0.077 89.749 2011
CoRoT-23 Serpens 15.63 G0IV b 2.8 1.08 3.6314 0.0477 0.16 85.7 2011
CoRoT-24 Monoceros 14.3 K1V b 0.018 0.33 5.1134 0.056 0 86.5 2011
c 0.088 0.44 11.759 0.098 0 2011
CoRoT-25 Ophiuchus 15th G0V b 0.27 1.08 4.86069 0.0578 84.5 2012
CoRoT-26 Ophiuchus 15.76 G8IV b 0.52 1.26 4.20474 0.0526 0 86.8 2012
CoRoT-27 Serpens 15.54 G2 b 10.39 1.007 3.57532 0.0476 0.065 86.7 2012
CoRoT-28 Serpens 13.49 G8-G9IV b 0.484 0.955 5.20851 0.059 0.047 2012
CoRoT-29 Ophiuchus 15.35 K0V b 0.85 0.9 2.85057 0.039 0.082 87.3 2012
CoRoT-30 Ophiuchus 15.66 G3V b 2.84 1.02 9.06005 0.084 0.007 890 2017
CoRoT-31 Monoceros 15.7 G2IV b 0.84 1.46 4,62941 0.0586 0.02 83.2 2017
CoRoT-32 Monoceros 14th G0VI b 0.15 0.57 6.71837 0.071 89 2017
CoRoT-33 Ophiuchus 14.7 G9V b 59.2 1.1 5,819143 0.0579 0.07 85.5 2015

Asteroseismology

In 2008, COROT discovered three distant stars that are surprisingly physically similar to our sun . Periodic fluctuations in brightness were found in all three stars, as are typical for stars similar to the sun. Such fluctuations had never been documented with the precision Corot achieved. From the fluctuations, conclusions could be drawn about the vibrational states of the star bodies. All three stars also showed the sun-typical granulation of the star surface. This is created by patterns in the convective ascent of particularly hot plasma from deeper layers of the star on its surface.

Operation in orbit

  • March 8, 2009: Permanent failure of the message transmission from the CCDs A1 and E1 (first photogrammetric chain), problems with the satellite software.
  • April 7, 2009: Corot realigned to the star field LRc03 in the constellation Snake , which is particularly suitable for the search for exoplanets. Resumption of scientific data collection - but only with the undisturbed CCDs A2 and E2 (second photogrammetric chain).
  • October 23, 2009: The CNES, together with its national and international partners, decided to extend COROT's active mission by three years until March 31, 2013.
  • November 2, 2012: Due to a computer failure, no more data can be recorded. It is still unclear whether the defect can be remedied.
  • June 20, 2013: Mission completed.
  • December 23, 2013: lowering of the orbit. This orbit maneuver, scheduled for January 2014, was brought forward because there was a threat of a collision with a missile stage.
  • June 17, 2014: Last radio connection with COROT. Satellite was switched off.

See also

literature

  • Tilmann Althaus: The COROT mission. A planet hunter in space. In: Stars and Space 46, No. 1, 2007, ISSN  0039-1263 , pp. 16-18 (2007)

Individual evidence

  1. COROT - orbit. Retrieved November 29, 2014 .
  2. ^ Interruption of the mission. CNES, November 20, 2012, accessed November 27, 2012 .
  3. a b c CNES press release: Mission accomplie pour le satellite CoRoT , June 20, 2013 (French)
  4. a b c Dernière télécommande pour CoRoT. CNES, June 18, 2014, accessed May 5, 2017 (French).
  5. Flight Acceptance Review, in Cannes, from 5 to 7 September 2006. CNES, September 2006, accessed on July 1, 2014 (French).
  6. COROT on its way (English) - Article at the European Space Agency (ESA) of December 27, 2006
  7. a b The CoRoT satellite: 3 more years to hunt for planets and to listen to the music of stars. (PDF) CNES, October 26, 2009, accessed May 5, 2017 (English).
  8. Stephen Clark: Scientists losing hope of reviving French telescope , spaceflightnow.com, January 4, 2013, accessed May 26, 2013
  9. ^ CoRoT. Kuffner Observatory Association, accessed on May 26, 2013 .
  10. a b 01/2014 - CoRoT: évitement de collision et retrait de service. CNES, January 2014, accessed on January 13, 2014 (French): "L'extinction définitive du satellite est prévue à la fin du printemps 2014."
  11. Encyclopedia of Exoplanets (exoplanet.eu)
  12. COROT discovers first exoplanets - article at astronews.com , May 4, 2007
  13. Bouchy et al. (2008). "Radial velocity follow-up for confirmation and characterization of transiting exoplanets". http://arxiv.org/PS_cache/arxiv/pdf/0902/0902.3520v1.pdf , accessed April 27, 2009
  14. CoRoT-6 b (English) - EPE entry , April 16, 2009
  15. COROT discovers first transiting terrestrial planet - Article at ScienceBlogs , February 3, 2009
  16. a b http://www.corot.de/german/news.htm#Exo7
  17. a b c d [1] (PDF; 513 kB) Abundant harvest of exoplanets - press release by the Corot team from June 14, 2010
  18. http://www.cnes.fr/web/CNES-fr/8391-gp-une-planete-temperee-decouverte-par-corot.php
  19. http://www.esa.int/SPECIALS/COROT/SEMJOMCKP6G_0.html
  20. http://smsc.cnes.fr/COROT/oscillation_200811.htm
  21. Eric Hand: Exoplanet hunter nears its end. Nature, November 16, 2012, accessed November 18, 2012 .

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