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NASA Artist Impression of Kepler-37b
Discovery date February 20, 2013[1]
Orbital characteristics
0.1003 AU[2]
13.367308 d[1]
Inclination 88.63°[2]
Physical characteristics
Mean radius
0.303 R[2]
1930 km
Mass >0.01 M[3]
<6 M[4][5][a]
Temperature 700 K[6]

Kepler-37b is an extrasolar planet (exoplanet) orbiting Kepler-37 in the constellation Lyra.[7] As of February 2013 it is the smallest planet discovered around a main-sequence star, with a radius slightly greater than that of the Moon.[8] The measurements do not constrain its mass, but masses above a few times that of the Moon give unphysically high densities.[5]


A size comparison of the planets in the Kepler-37 system and objects in the Solar System

Kepler-37b, along with two other planets, Kepler-37c and Kepler-37d, were discovered by the Kepler space telescope, which observes stellar transits.[1][6] After observing transits of Kepler-37b, astronomers had to compare it with the size of the parent star.

The size of the star was obtained using asteroseismology;[clarification needed][9] Kepler-37 is currently the smallest star to be studied using this process.[6] This allowed the size of Kepler-37b to be determined "with extreme accuracy".[6]

To date, Kepler-37b is the smallest planet discovered around a main-sequence star[b] outside the Solar System.[8] Detection of Kepler-37b was possible due to its short orbital period, relative brightness, and low activity of its host star, allowing brightness data to average out quickly.[10] The discovery of Kepler-37b has led Jack Lissauer, a scientist at NASA's Ames Research Center, to conjecture that "such little planets are common".[6]


Kepler-37b orbits its parent star at a distance of about 15 million kilometers (9.3 million miles), with a period of roughly 13 days.[8] The outer two planets in the system have orbital periods[1][2] within one percent of the 8:5 and 3:1 resonances with Kepler-37b's period.

Physical properties[edit]

Kepler-37b is located approximately 210 light-years from Earth.[11] It is slightly larger than the Moon, with a diameter of about 3,900 kilometres (2,400 mi).[9] NASA states that it probably has no atmosphere and cannot support life.[6] Furthermore, it is most likely composed of rocky materials.[6] Because it is so close to its star (Mercury is more than three times as far from the Sun), Kepler-37b's mean temperature is estimated to be around 425 °C (800 °F).[6]

See also[edit]


  1. ^ Masses more than a few times that of the Moon result in unphysically high densities.
  2. ^ The pulsar planet PSR B1257+12 A has a comparable mass. The actual size of PSR B1257+12 A is unknown, but is likely comparable to Kepler-37b.


  1. ^ a b c d e Barclay, T.; Rowe, J. F.; Lissauer, J. J.; Huber, D.; Fressin, F.; Howell, S. B.; Bryson, S. T.; Chaplin, W. J.; Désert, J. M. (2013-02-20). "A sub-Mercury-sized exoplanet". Nature (journal) 494 (7438): 452–4. arXiv:1305.5587. Bibcode:2013Natur.494..452B. doi:10.1038/nature11914. ISSN 0028-0836. PMID 23426260. Retrieved 2013-02-21. 
  2. ^ a b c d "Kepler-37 System". Retrieved February 21, 2013. 
  3. ^
  4. ^
  5. ^ a b [1]
  6. ^ a b c d e f g h "NASA's Kepler Mission Discovers Tiny Planet System". NASA. February 20, 2013. Retrieved February 21, 2013. 
  7. ^ Smallest Alien Planet Kepler-37b Explained (Infographic)
  8. ^ a b c "Tiniest Planet Yet Discovered by NASA Outside our Solar System". February 21, 2013. Retrieved February 21, 2013. 
  9. ^ a b "Astronomers Find the Tiniest Exoplanet Yet". Slate. February 20, 2013. Retrieved February 21, 2013. 
  10. ^ Centauri Dreams - Small Planets Confirm Kepler’s Capabilities
  11. ^ "NASA, using Kepler space telescope, finds smallest planet yet". Los Angeles Times. February 20, 2013. Retrieved February 21, 2013. 


Preceded by
PSR B1257+12 A
Least massive exoplanet[citation needed]
Succeeded by
Preceded by
Kepler-42 d
Smallest-volume exoplanet
Succeeded by