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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 14.3078s[1]
Declination 44° 31′ 05.389″[1]
Apparent magnitude (V) 9.710[2]
Spectral type G8V
Proper motion (μ) RA: −60.520±0.053[1] mas/yr
Dec.: 48.694±0.050[1] mas/yr
Parallax (π)15.6155 ± 0.0290[1] mas
Distance208.9 ± 0.4 ly
(64.0 ± 0.1 pc)
Mass0.803 (± 0.07)[3] M
Radius0.77 (± 0.026)[3] R
Temperature5417 (± 75)[3] K
Metallicity [Fe/H]–0.32 (± 0.07)[3] dex
Rotational velocity (v sin i)1.1 (± 1.1)[3] km/s
Age5.66 Gyr
Other designations
KOI-245, KIC 8478994,[2] TYC 3131-1199-1[4]
Database references
Extrasolar Planets

Kepler-37, also known as UGA-1785,[5][6][7] is a G-type main-sequence star located in the constellation Lyra 209 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.[8] 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,[9] 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.[10]

Planetary system[edit]

The Kepler-37 planetary system[8]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 0.01[a] M 0.1003 13.367308 88.63° 0.354 R
c 0.1368 21.301886 89.07° 0.742 R
d 0.2076 39.792187 89.335° 1.99 R
e 0.2508 51.196

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.[11] At 3,865 kilometres (2,402 mi) in diameter, it is slightly larger than the Moon.[11] It orbits Kepler-37 once every 13 days at a distance of about 0.1 astronomical units (AU).[8] 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.[11] Surface temperature is estimated at 700 K (427 °C; 800 °F).[10]

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.[8] Neither is able to support water due to their proximity to Kepler-37.[11]

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


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.[8] 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.[8] The exoplanets were considerably smaller than any previously detected, leading Science World Reports to state that "a major technological improvement for the telescope" had been achieved.[11]

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.[12] However, he does not anticipate finding many planets as small as Kepler-37b due to the very small amount of light such planets obscure.[12] 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."[10] 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.[12]

The asteroseismology work was, in part, paid for by White Dwarf Research Corporation, a crowd funded non-profit organization.[13]

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.[14]


  1. ^ Masses more than a few times that of the Moon result in unphysically high densities.


  1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia Data Release 2 Vizier catalog entry
  2. ^ a b "Kepler Host Star Characteristics". Archive for Space Telescopes. STSI. 2012-02-24. Retrieved 2013-02-21.
  3. ^ a b c d e Barclay, T; Rowe, JF; Lissauer, JJ; et al. (2013-02-20). "A sub-Mercury-sized exoplanet (Additional Information)" (PDF). Nature. 494 (7438): 452–4. arXiv:1305.5587. Bibcode:2013Natur.494..452B. doi:10.1038/nature11914. PMID 23426260. Retrieved 2013-02-21.
  4. ^ "TYC 3131-1199-1". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2013-02-22.
  5. ^ Planets in Kepler-37 star system designated ‘UGA-1785’ by NASA
  6. ^ 211 light years away, star system named for UGA
  7. ^ Kepler-37, Open Exoplanet catalogue
  8. ^ 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.
  9. ^ Smallest Alien Planet Kepler-37b Explained (Infographic)
  10. ^ a b c "NASA's Kepler Mission Discovers Tiny Planet System" (Press release). NASA. February 20, 2012. Retrieved February 21, 2012.
  11. ^ 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.
  12. ^ a b c Eryn Brown (February 21, 2013). "NASA, using Kepler space telescope, finds smallest planet yet". LA Times. Retrieved February 21, 2013.
  13. ^ Phil Plait (February 20, 2013). "Astronomers Find the Tiniest Exoplanet Yet". Bad Astronomy blog. Slate. Retrieved February 21, 2013.
  14. ^ Hadden, Sam; Lithwick, Yoram (2014). "Densities and Eccentricities of 139 Kepler Planets from Transit Time Variations". The Astrophysical Journal. 787: 80. arXiv:1310.7942. Bibcode:2014ApJ...787...80H. doi:10.1088/0004-637X/787/1/80.

Further reading[edit]

External links[edit]

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