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A Moon-size Line Up.jpg
Line up comparing the Kepler-37 planets system to the moon and planets in the Solar System.
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 18h 56m 14.28s[1]
Declination 44° 31′ 5.52″[1]
Apparent magnitude (V) 9.710[1]
Spectral type G
Distance 215 ly
(66[2] pc)
Mass 0.803 ± 0.068[2] M
Radius 0.770 ± 0.026[2] R
Temperature 5417 ± 75[2] K
Metallicity [Fe/H] –0.32 ± 0.07[2] dex
Rotational velocity (v sin i) 1.1 ± 1.1[2] km/s
Age 6[2] Gyr
Other designations
KOI-245, KIC-8478994,[1] TYC 3131-1199-1 [3]

Kepler-37 is a G-type main-sequence star located in the constellation Lyra 215.2 light years from Earth. It is host to exoplanets Kepler-37b, Kepler-37c, Kepler-37d and Kepler-37e, all of which orbit very close to it. Kepler-37 has a mass about 80.3 percent of the Sun's and a radius about 77 percent as large.[4] It has a temperature similar to that of the Sun, but a bit cooler at 5,417 K. It has about half the metallicity of our Sun. With an age of roughly 6 billion years,[5] it is slightly older than the Sun, but is still a main-sequence star. Until January 2015, Kepler-37 was the smallest star to be measured via asteroseismology.[6]

Planetary system[edit]

Kepler-37b is the closest planet to the Kepler-37. At the time of its discovery in February 2013, it was the smallest known exoplanet.[7] At 3,865 kilometres (2,402 mi) in diameter, it is slightly larger than the Moon.[7] It orbits Kepler-37 once every 13 days at a distance of about 0.1 astronomical units (AU).[4] Kepler-37b has a rocky surface and is believed to be too small and too close to its star to support water or maintain an atmosphere.[7] Surface temperature is estimated at 700 K (427 °C; 800 °F).[6]

Kepler-37c is around three-quarters of the diameter of Earth and orbits approximately every 21 days at a distance of just under 0.14 AU. Kepler-37d is about twice the diameter of Earth. It orbits in around 40 days at a distance of nearly 0.21 AU.[4] Neither is able to support water due to their proximity to Kepler-37.[7]

The periods of the three inner planets are close (within one per cent) to a 5:8:15 mean-motion resonance relationship.

The Kepler-37 planetary system[4]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b ≥ 0.00003 MJ 0.1003 13.367308 88.63° 0.303 R
c — MJ 0.1368 21.301886 89.07° 0.742 R
d — MJ 0.2076 39.792187 89.335° 1.99 R
e — MJ 0.2508 51.196


The Kepler planets were discovered in September 2012 with the aid of transit events detected by the Kepler space telescope, and announced to the public in February 2013.[4] Computer simulation was used to rule out other astronomical phenomenon mimicking planetary transit with probabilities of error <0.05% (3σ) for each potential planet. Additionally, simulation demonstrated that the proposed planetary configuration was stable.[4] The exoplanets planets were considerably smaller than any previously detected, leading Science World Reports to state that "a major technological improvement for the telescope" had been achieved.[7]

Thomas Barclay, an astrophysicist on the Kepler space telescope team, said the discovery was "really good news" in the search for hospitable planets, a prime objective of the project, because it demonstrated the telescope was capable of detecting Earth-sized planets.[8] However, he does not anticipate finding many planets as small as Kepler-37b due to the very small amount of light such planets obscure.[8] According to NASA scientist Jack Lissauer, the discovery of Kepler-37b "suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data."[6] Astronomer John Johnson of Caltech university said the discovery would have been "unimaginable" a few years ago and that the telescope had revolutionized astronomers' picture of the universe.[8]

The asteroseismology work was, in part, paid for by White Dwarf Research Corporation, a crowd funded non-profit organization.[9]

In 2014, a fourth planet with orbital period of 51 days was confirmed through transit timing variations. Previously this signal was thought to be a false positive.[10]


  1. ^ a b c d "Kepler Host Star Characteristics". Archive for Space Telescopes. STSI. 2012-02-24. Retrieved 2013-02-21. 
  2. ^ a b c d e f g "A sub-Mercury-sized exoplanet (Additional Information)" (PDF). Nature. 2013-02-20. Retrieved 2013-02-21. 
  3. ^ "SIMBAD Query Result: TYC 3131-1199-1 -- Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2013-02-22. (KOI-245)
  4. ^ a b c d e f Barclay, T.; Rowe, J. F.; Lissauer, J. J.; Huber, D.; Fressin, F.; Howell, S. B.; Bryson, S. T.; Chaplin, W. J.; Désert, J.-M.; Lopez, Eric D.; Marcy, Geoffrey W.; Mullally, Fergal; Ragozzine, Darin; Torres, Guillermo; Adams, Elisabeth R.; Agol, Eric; Barrado, David; Basu, Sarbani; Bedding, Timothy R.; Buchhave, Lars A.; Charbonneau, David; Christiansen, Jessie L.; Christensen-Dalsgaard, Jørgen; Ciardi, David; Cochran, William D.; Dupree, Andrea K.; Elsworth, Yvonne; Everett, Mark; Fischer, Debra A. et al. (2013-02-20). "A sub-Mercury-sized exoplanet". Nature 494 (7438): 452–4. arXiv:1305.5587. Bibcode:2013Natur.494..452B. doi:10.1038/nature11914. ISSN 0028-0836. PMID 23426260. Retrieved 2013-02-21. 
  5. ^ Smallest Alien Planet Kepler-37b Explained (Infographic)
  6. ^ a b c "NASA's Kepler Mission Discovers Tiny Planet System" (Press release). NASA. February 20, 2012. Retrieved February 21, 2012. 
  7. ^ a b c d e Catherine Griffin (February 21, 2013). "Tiniest Planet Yet Discovered by NASA Outside our Solar System". Science World Report. Retrieved February 21, 2013. 
  8. ^ a b c Eryn Brown (February 21, 2013). "NASA, using Kepler space telescope, finds smallest planet yet". LA Times. Retrieved February 21, 2013. 
  9. ^ Phil Plait (February 20, 2013). "Astronomers Find the Tiniest Exoplanet Yet". Bad Astromony blog (Slate). Retrieved February 21, 2013. 
  10. ^

Further reading[edit]

External links[edit]