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Exoplanet List of exoplanets
Artist's impression of Kepler-37b.
Parent star
Star Kepler-37
Constellation Lyra
Right ascension (α) 18h 56m 14.32s
Declination (δ) +44° 31′ 05.3″
Apparent magnitude (mV) 9.71
Distance 215.2 ly
(66 pc)
Spectral type G8V
Mass (m) 0.80 (± 0.07) M
Radius (r) 0.77 (± 0.03) R
Temperature (T) 5417 (± 75) K
Metallicity [Fe/H] −0.32 (± 0.07)
Age 5.66 Gyr
Physical characteristics
Mass (m) 0.01+5.99
[1][2][3][a] M
Radius (r) 0.354 (± 0.014) R
Stellar flux (F) 45.53
Temperature (T) 700 K (427 °C; 800 °F)[4]
Orbital elements
Semi-major axis (a) 0.1003[5] AU
Eccentricity (e) 0.080+0.210
Orbital period (P) 13.367308[6] d
Inclination (i) 88.63[5]°
Discovery information
Discovery date February 20, 2013[6]
Discovery method Transit (Kepler Mission)
Discovery site Kepler Space Observatory
Discovery status Published
Other designations
KOI-245.01, KOI-245 b, KIC-8478994 b, TYC 3131-1199-1 b
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

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.[3]


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

Mass, radius and temperature[edit]

Kepler-37b is a sub-Earth, an exoplanet with a radius and mass smaller than Earth. Its surface temperature is 700 K (427 °C; 800 °F). Because of this, it is not expected to have an atmosphere.[4] Its radius is approximately 0.34 R (about a diameter of 3,900 kilometres (2,400 mi)), about a little larger than the Moon.[9] Due to its small size, it is very likely Kepler-37b is a rocky planet with a solid surface.[4] Furthermore, it is too hot to support liquid water on its surface.[4]

Host star[edit]

The planet orbits a (G-type) star similar to the Sun, named Kepler-37, orbited by a total of four planets. The star has a mass of 0.80 M and a radius of 0.79 R. It has a temperature of 5417 K and is 5.66 billion years old. In comparison, the Sun is 4.6 billion years old[10] and has a temperature of 5778 K.[11]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 9.71. Therefore, it is too dim to be seen with the naked eye.


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 at a distance of 0.1 AU (compared to Mercury's distance from the Sun, which is about 0.38 AU).[8] The outer two planets in the system have orbital periods[6][5] within one percent of the 8:5 and 3:1 resonances with Kepler-37b's period.


Kepler-37b, along with two other planets, Kepler-37c and Kepler-37d, were discovered by the Kepler space telescope, which observes stellar transits.[6][4] 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;[9] Kepler-37 is currently the smallest star to be studied using this process.[4] This allowed the size of Kepler-37b to be determined "with extreme accuracy".[4]

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.[12] 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".[4]

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. ^
  2. ^
  3. ^ a b [1]
  4. ^ a b c d e f g h "NASA's Kepler Mission Discovers Tiny Planet System". NASA. February 20, 2013. Retrieved February 21, 2013. 
  5. ^ a b c "Kepler-37 System". Retrieved February 21, 2013. 
  6. ^ a b c d 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. 494 (7438): 452–4. arXiv:1305.5587Freely accessible. Bibcode:2013Natur.494..452B. doi:10.1038/nature11914. ISSN 0028-0836. PMID 23426260. Retrieved 2013-02-21. 
  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. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011. 
  11. ^ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011. 
  12. ^ Centauri Dreams - Small Planets Confirm Kepler’s Capabilities
Preceded by
PSR B1257+12 A
Least massive exoplanet[citation needed]
Succeeded by
Preceded by
Kepler-42 d
Smallest-radius exoplanet
Succeeded by

Coordinates: Sky map 18h 56m 14.32s, +44° 31′ 05.3″