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Kepler in orbit
Artist's impression of the Kepler telescope
Mission type Space Telescope
Operator LASP NASA
COSPAR ID 2009-011A
SATCAT no. 34380
Mission duration planned: 3.5 years
elapsed: 8 years, 6 months and 19 days
Spacecraft properties
Manufacturer Ball Aerospace & Technologies Corp.
Launch mass 1,052.4 kg (2,320 lb)[1]
Dry mass 1,040.7 kg (2,294 lb)
Payload mass 478 kg (1,054 lb)
Dimensions 4.7 m × 2.7 m (15.4 ft × 8.9 ft)
Power 1100 watts
Start of mission
Launch date March 7, 2009, 03:49:57 (2009-03-07UTC03:49:57Z) UTC[2]
Rocket Delta II (7925-10L)
Launch site Space Launch Complex 17-B
Cape Canaveral Air Force Station
Contractor United Launch Alliance
Entered service May 12, 2009, 09:01 (2009-05-12UTC09:01Z) UTC
Orbital parameters
Reference system Heliocentric
Regime Earth-trailing
Period 372.5 days
Main Telescope
Type Schmidt camera
Diameter 0.95 m (3.1 ft)
Collecting area 0.708 m2[A]
Wavelengths 400–865 nm[3]
Band X band (TT&C)
Ka band (data acquisition)
Bandwidth few kbit/s (X Band)
~4.3 Mbit/s (Ka band)

Kepler is a space observatory launched by NASA to discover Earth-like planets orbiting other stars.[5] The spacecraft, named after the Renaissance astronomer Johannes Kepler,[6] was launched on March 7, 2009.[7]

Designed to survey a portion of our region of the Milky Way to discover dozens of Earth-size extrasolar planets in or near the habitable zone and estimate how many of the billions of stars in our galaxy have such planets,[8][9] Kepler's sole instrument is a photometer that continually monitors the brightness of over 145,000 main sequence stars in a fixed field of view.[10] This data is transmitted to Earth, then analyzed to detect periodic dimming caused by extrasolar planets that cross in front of their host star.

Kepler is part of NASA's Discovery Program of relatively low-cost, focused primary science missions. The telescope's construction and initial operation were managed by NASA's Jet Propulsion Laboratory, with Ball Aerospace responsible for developing the Kepler flight system. The Ames Research Center is responsible for the ground system development, mission operations since December 2009, and science data analysis. The initial planned lifetime was 3.5 years,[11] but greater-than-expected noise in the data, from both the stars and the spacecraft, meant additional time was needed to fulfill all mission goals. Initially, in 2012, the mission was expected to last until 2016,[12] but this would only have been possible if all remaining reaction wheels used for pointing the spacecraft remained reliable.[13] On May 11, 2013, a second of four reaction wheels failed, disabling the collection of science data[14] and threatening the continuation of the mission.[15]

As of June 2014, Kepler and its follow-up observations had found 977 confirmed exoplanets in more than 400 stellar systems, along with a further 3,277 unconfirmed planet candidates.[B][16][17] In November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy.[18][19][20] 11 billion of these estimated planets may be orbiting sun-like stars.[21] The nearest such planet may be 12 light-years away, according to the scientists.[18][19]

On August 15, 2013, NASA announced that they had given up trying to fix the two failed reaction wheels. This meant the current mission needed to be modified, but it did not necessarily mean the end of planet-hunting. NASA had asked the space science community to propose alternative mission plans "potentially including an exoplanet search, using the remaining two good reaction wheels and thrusters".[22][23][24][25] On November 18, 2013, the K2 (also named "Second Light") plan proposal, which would include utilizing the disabled Kepler in a way that could detect habitable planets around smaller, dimmer red dwarf stars, was reported.[26][27][28][29] On May 16, 2014, NASA announced the approval of extending the Kepler mission to the K2 mission.[30]


Kepler being loaded onto its upper stage

The spacecraft has a mass of 1,039 kilograms (2,291 lb) and contains a 1.4-meter (55 in) primary mirror feeding an aperture of 0.95-meter (37.4 in) – at the time of its launch this was the largest mirror on any telescope outside Earth orbit.[31] The spacecraft has a 115 deg2 (about 12-degree diameter) field of view (FOV), roughly equivalent to the size of one's fist held at arm's length. Of this, 105 deg2 is of science quality, with less than 11% vignetting. The photometer has a soft focus to provide excellent photometry, rather than sharp images. The mission goal is a combined differential photometric precision (CDPP) of 20 ppm for a m(V)=12 solar-like star for a 6.5-hour integration, though the observations so far have fallen short of this objective (see mission status). An Earth-like transit produces a brightness change of 84 ppm and lasts for thirteen hours when it crosses the center of the star.


Kepler's image sensor array. The array is curved to account for Petzval field curvature.

The focal plane of the spacecraft's camera is made up of 42 CCDs at 2200x1024 pixels, which made it at the time the largest camera yet launched into space, possessing a total resolution of 95 megapixels.[32][33] The array is cooled by heat pipes connected to an external radiator.[34] The CCDs are read out every six seconds (to limit saturation) and co-added on board for 58.89 seconds for short cadence targets, and 1765.5 seconds (29.4 minutes) for long cadence targets. Due to the larger bandwidth requirements for the former, these are limited in number to 512 compared to ~160,000 for long cadence. However, even though at launch Kepler had the highest data rate of any NASA mission, the 29-minute sums of all 95 million pixels constitute more data than can be stored and sent back to Earth. Therefore the science team has pre-selected the relevant pixels associated with each star of interest, amounting to about 6 percent of the pixels (5.4 megapixels). The data from these pixels is then requantized, compressed and stored, along with other auxiliary data, in the on-board 16 gigabyte solid-state recorder. Data that is stored and downlinked includes science stars, p-mode stars, smear, black level, background and full field-of-view images.[34][35]

Second Light (K2)[edit]

In November 2013, a newly proposed mission plan, initially named "K2" (also called "Second Light"), was presented for consideration.[27][28][29][36] K2 would involve using Kepler's remaining capability, photometric precision of about 300 parts per million, compared with about 20 parts per million earlier, to collect data for the study of "supernova explosions, star formation and solar-system bodies such as asteroids and comets, ... " and for finding and studying more exoplanets.[27][28][36] In this proposed mission plan, Kepler would search a much larger area in the plane of earth's orbit around the sun.[27][28][36]

Kepler's "Second Light" (K2) Proposal Explained (December 11, 2013).[28]

In early 2014, the spacecraft underwent successful testing for the K2 mission.[37] From March to May 2014, data from a new field called Field 0 was collected as a testing run.[38] On May 16, 2014, NASA announced the approval of extending the Kepler mission to the K2 mission.[30] Kepler's photometric precision for the K2 mission is estimated to be 50 ppm on a magnitude 12 star for a 6.5 hour integration.[39] In February 2014, photometric precision for the K2 mission using two-wheel, fine-point precision operations was measured as 44 ppm on magnitude 12 stars for a 6.5 hour integration. The analysis of these measurements posted by NASA stated that the measurements "suggest" the K2 photometric precision "approaches" that of the Kepler archive of three-wheel, fine-point precision data.[40]

Field 1 of the K2 mission is set towards the Leo-Virgo region of the sky and Field 2 is towards the "head" area of Scorpius and includes two globular clusters: Messier 4 and Messier 80[41] and part of the Scorpius–Centaurus Association which is only about 11 million years old[42] and at a distance of 380-470 light years[43] with probably over 1000 members.[44]

Data releases[edit]

The Kepler team originally promised to release data within one year of observations.[45] However, this plan was changed after launch, with data being scheduled for release up to three years after its collection.[46] This resulted in considerable criticism,[47][48][49][50][51] leading the Kepler science team to release the third quarter of their data one year and nine months after collection.[52] The data through September 2010 (quarters 4, 5, and 6) was made public in January 2012.[53]

See also[edit]

Related or comparable missions and projects


  1. ^ Aperture of 0.95 m yields a light-gathering area of Pi×(0.95/2)2 = 0.708 m2; the 42 CCDs each sized 0.050 m × 0.025m yields a total sensor area of 0.0525 m2:[4]
  2. ^ This does not include Kepler candidates without a KOI designation, such as circumbinary planets, or candidates found in the Planet Hunters project.


  1. ^ "Kepler: FAQ". NASA Ames Research Center. Retrieved March 25, 2014.  
  2. ^ This ref was orphaned. 
  3. ^ NASA Staff (2010). "Kepler Mission: Photometer and Spacecraft". NASA. Retrieved February 2, 2011.  
  4. ^ Staff (June 26, 2013). "Kepler Spacecraft and Instrument | NASA". Archived from the original on January 18, 2014. Retrieved January 18, 2014.  
  5. ^ Koch, David; Gould, Alan (March 2009). "Kepler Mission". NASA. Retrieved March 14, 2009.  
  6. ^ DeVore, Edna (June 9, 2008). "Closing in on Extrasolar Earths". Retrieved March 14, 2009.  External link in |work= (help) 
  7. ^ NASA Staff. "Kepler Launch". NASA. Retrieved September 18, 2009.  
  8. ^ NASA Staff. "Kepler Mission/QuickGuide". NASA. Retrieved April 20, 2011.  Supports:"survey a portion of our region", "near the habitable zone and estimate how"
  9. ^ Overbye, Dennis (12 May 2013). "Finder of New Worlds". New York Times. Retrieved 13 May 2014.  Supports:"of Earth-size extrasolar planets in", "the Milky Way to discover"
  10. ^ AAS Staff. "Meeting Program and Block Schedule". American Astronomical Society. Retrieved April 20, 2011.  – click the itinerary builder to get to the abstract of "Kepler Planet Detection Mission: Introduction and First Results". 
  11. ^ BBC Staff (March 7, 2009). "Nasa launches Earth hunter probe". BBC News. Retrieved March 14, 2009.  
  12. ^ "NASA Extends Planet-Hunting Kepler Mission Through 2016". April 4, 2012. Retrieved May 2, 2012. 
  13. ^ Stephen Clark (October 16, 2012). "Kepler's exoplanet survey jeopardized by two issues". Spaceflight Now. Retrieved October 17, 2012.  
  14. ^ NASA - Kepler Mission Manager Update (May 21, 2013) 
  15. ^ "Equipment Failure May Cut Kepler Mission Short". May 15, 2013. Retrieved May 15, 2013.  
  16. ^ Wall, Mike (June 14, 2013). "Ailing NASA Telescope Spots 503 New Alien Planet Candidates". TechMediaNetwork. Retrieved June 15, 2013. 
  17. ^ "NASA's Exoplanet Archive KOI table". NASA. Retrieved February 28, 2014. 
  18. ^ a b Overbye, Dennis (November 4, 2013). "Far-Off Planets Like the Earth Dot the Galaxy". New York Times. Retrieved November 5, 2013. 
  19. ^ a b Petigura, Eric A.; Howard, Andrew W.; Marcy, Geoffrey W. (October 31, 2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences of the United States of America. doi:10.1073/pnas.1319909110. Retrieved November 5, 2013. 
  20. ^ Staff (January 7, 2013). "17 Billion Earth-Size Alien Planets Inhabit Milky Way". Retrieved January 8, 2013. 
  21. ^ Khan, Amina (November 4, 2013). "Milky Way may host billions of Earth-size planets". Los Angeles Times. Retrieved November 5, 2013. 
  22. ^ "NASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions Considered". August 15, 2013. Retrieved August 15, 2013. 
  23. ^ Overbye, Dennis (August 15, 2013). "NASA’s Kepler Mended, but May Never Fully Recover". New York Times. Retrieved August 15, 2013. 
  24. ^ Wall, Mike (August 15, 2013). "Planet-Hunting Days of NASA's Kepler Spacecraft Likely Over". Retrieved August 15, 2013. 
  25. ^ "Kepler: NASA retires prolific telescope from planet-hunting duties". 
  26. ^ Overbye, Dennis (November 18, 2013). "New Plan for a Disabled Kepler". New York Times. Retrieved November 18, 2013. 
  27. ^ a b c d Johnson, Michele (November 25, 2013). Johnson, Michele, ed. "A Sunny Outlook for NASA Kepler's Second Light". NASA Official: Brian Dunbar; Image credits: NASA Ames; NASA Ames/W Stenzel. NASA. Archived from the original on April 17, 2014. Retrieved December 12, 2013. 
  28. ^ a b c d e Johnson, Michele (December 11, 2013). Johnson, Michele, ed. "Kepler's Second Light: How K2 Will Work". NASA Official: Brian Dunbar; Image credit: NASA Ames/W Stenzel. NASA. Archived from the original on April 17, 2014. Retrieved December 12, 2013.  
  29. ^ a b Hunter, Roger (December 11, 2013). Johnson, Michele, ed. "Kepler Mission Manager Update: Invited to 2014 Senior Review". NASA Official: Brian Dunbar;. NASA. Archived from the original on April 17, 2014. Retrieved December 12, 2013. 
  30. ^ a b Sobeck, Charlie (May 16, 2014). Johnson, Michele, ed. "Kepler Mission Manager Update: K2 Has Been Approved!". NASA Official: Brian Dunbar; Image credit(s): NASA Ames/W. Stenzel. NASA. Archived from the original on May 17, 2014. Retrieved May 17, 2014. 
  31. ^ Atkins, William (December 28, 2008). "Exoplanet Search Begins with French Launch of Corot Telescope Satellite". iTWire. Retrieved May 6, 2009. 
  32. ^ NASA Staff. "Kepler: Spacecraft and Instrument". NASA. Retrieved May 1, 2009. 
  33. ^ NASA Staff (April 16, 2009). "Kepler's Diamond Mine of Stars". NASA. Retrieved May 1, 2009. 
  34. ^ a b NASA Staff (February 2009). "Kepler: NASA's First Mission Capable of Finding Earth-Size Planets" (PDF). NASA. Retrieved March 14, 2009. 
  35. ^ "PyKE Primer - 2. Data Resources". NASA. Retrieved March 12, 2014. 
  36. ^ a b c Wall, Mike (November 5, 2013). "NASA's Hobbled Planet-Hunting Spacecraft May Resume Search for Alien Worlds". Image credit: NASA. TechMediaNetwork. Archived from the original on April 17, 2014. Retrieved April 17, 2014. 
  37. ^ Hunter, Roger (February 14, 2014). Johnson, Michele, ed. "Kepler Mission Manager Update: K2 spacecraft operation tests continue". NASA Official: Brian Dunbar; Image Credit: NASA Ames/T. Barclay. NASA. Archived from the original on April 17, 2014. Retrieved April 17, 2014. 
  38. ^ Bakos, G. Á.; Hartman, J. D.; Bhatti, W.; Bieryla, A.; de Val-Borro, M.; Latham, D. W.; Buchhave, L. A.; Csubry, Z.; Penev, K.; Kovács, G.; Béky, B.; Falco, E.; Kovács, T.; Howard, A. W.; Johnson, J. A.; Isaacson, H.; Marcy, G. W.; Torres, G.; Noyes, R. W.; Berlind, P.; Calkins, M. L.; Esquerdo, G. A.; Lázár, J.; Papp, I.; Sári, P. (April 17, 2014). "HAT-P-54b: A Hot Jupiter Transiting a 0.64 Msun Star in Field 0 of the K2 Mission" (PDF). astro-ph.EP. Ithaca, New York: Cornell University Library. arXiv:1404.4417v1Freely accessible. Retrieved June 12, 2014.  External link in |journal= (help)
  39. ^ Still, Martin, ed. (May 29, 2014). "Kepler Guest Observer Program". NASA Official: Jessie Dotson. Archived from the original on June 12, 2014. Retrieved June 12, 2014. 
  40. ^ Still, Martin, ed. (May 29, 2014). "K2 Performance". NASA Official: Jessie Dotson. Archived from the original on June 12, 2014. Retrieved June 12, 2014. 
  41. ^ Molnár, L.; Plachy, E.; Szabó, R. (May 29, 2014). "Cepheids and RR Lyrae Stars in the K2 Fields" (PDF). astro-ph.SR. Ithaca, New York: Cornell University Library. arXiv:1405.7690v1Freely accessible. Retrieved May 31, 2014.  External link in |journal= (help) Supports:"Field 1 of the K2 mission is set", "sky and Field 2 is towards the"
  42. ^ Mark J. Pecaut, Eric E. Mamajek, & Eric J. Bubar (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association". Astrophysical Journal. 746 (2): 154. Bibcode:2012ApJ...746..154P. arXiv:1112.1695Freely accessible. doi:10.1088/0004-637X/746/2/154. 
  43. ^ de Zeeuw, P.T., Hoogerwerf, R., de Bruijne, J.H.J., Brown, A.G.A., & Blaauw, A. (1999). "A Hipparcos Census of Nearby OB Associations". Astronomical Journal. 117 (1): 354–399. Bibcode:1999AJ....117..354D. arXiv:astro-ph/9809227Freely accessible. doi:10.1086/300682. 
  44. ^ Mamajek, E.E., Meyer, M.R., & Liebert, J. (2002). "Post-T Tauri Stars in the Nearest OB Association". Astronomical Journal. 124 (3): 1670–1694. Bibcode:2002AJ....124.1670M. arXiv:astro-ph/0205417Freely accessible. doi:10.1086/341952. 
  45. ^ "Frequently Asked Questions from the Public". Retrieved September 6, 2011.  This Kepler FAQ states: "Data for each 3-month observation period will be made public within one year of the end the observation period".
  46. ^ "NASA's Kepler Mission Data Release Schedule". NASA. Retrieved October 18, 2011.  On this schedule, the data from the quarter ending June 2010 was scheduled to be released in June 2013.
  47. ^ Dennis Overbye (June 14, 2010). "In the Hunt for Planets, Who Owns the Data?". New York Times. 
  48. ^ Eric Hand (April 14, 2010). "Telescope team may be allowed to sit on exoplanet data". Nature. 
  49. ^ Alan MacRobert (August 2011). "Kepler's Exoplanets: A Progress Report". S ky and Telescope. 
  50. ^ Alex Brown (March 28–29, 2011). "Minutes of the Kepler Users Panel" (PDF). 
  51. ^ Nicole Gugliucci (June 15, 2010). "KEPLER EXOPLANET CONTROVERSY ERUPTS". Discovery news. 
  52. ^ "NASA's Kepler Mission Announces Next Data Release to Public Archive". 
  53. ^ "Kepler Data Collection and Archive Timeline". Retrieved January 1, 2012. 

Further reading[edit]

External links[edit]

Extrasolar planet catalogs and databases