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 the 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]

Kepler-37

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]
Characteristics
Spectral type	G8V
Astrometry
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 mas[1]
Distance	208.9 ± 0.4 ly (64.0 ± 0.1 pc)
Details
Mass	0.803 (± 0.07)[3] M☉
Radius	0.77 (± 0.026)[3] R☉
Temperature	5417 (± 75)[3] K
Metallicity [Fe/H]	–0.32 (± 0.07)[3] dex
Rotational velocity (v sin i)	1.1 (± 1.1)[3] km/s
Age	5.66 Gyr
Other designations
KOI-245, KIC 8478994,[2] TYC 3131-1199-1, BD+44 3020, 2MASS J18561431+4431052, GSC 03131-01199, Gaia DR2 2106674071344722688[4]
Database references
SIMBAD	data
Extrasolar Planets Encyclopaedia	data
KIC	data

Planetary system

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.[12] At 3,865 kilometres (2,402 mi) in diameter, it is slightly larger than the Moon.[12] 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.[12] 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 are able to support water due to their proximity to Kepler-37.[12]

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

In 2015, a grant was approved to further expand the Sagan Planet Walk by installing a Kepler-37d station on the Moon 384,500 kilometers (238,900 mi) away.[13]

Discovery

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.[12]

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.[14] However, he does not anticipate finding many planets as small as Kepler-37b due to the very small amount of light such planets obscure.[14] 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.[14]

The asteroseismology work was, in part, paid for by White Dwarf Research Corporation, a crowd funded non-profit organization.[15]

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,[16] and was claimed again to be a false positive in 2021.[11]

Notes

References

Further reading

• Barclay, Thomas; et al. (2013). "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. S2CID 205232792. (Supplementary information)

External links

• Media related to Kepler-37 at Wikimedia Commons
• Table of confirmed planets at NASA, Kepler mission

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