Kepler-37
G-type main-sequence star in the constellation Lyra
From Wikipedia, the free encyclopedia
Kepler-37, also known as UGA-1785,[8][9][10] is a G-type main-sequence star located in the constellation Lyra 209 light-years (64 parsecs) from Earth. It is host to exoplanets Kepler-37b, Kepler-37c, Kepler-37d and possibly 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.[6] It has a temperature similar to that of the Sun, but a bit cooler at 5,357 K. It has about half the metallicity of the Sun. With an age of roughly 6 billion years,[11] 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.[12]
Line up comparing the planets in the Kepler-37 system to the Moon and planets in the Solar System. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Lyra[1] |
| Right ascension | 18h 56m 14.30760s[2] |
| Declination | +44° 31′ 05.3896″[2] |
| Apparent magnitude (V) | 9.710[3] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | G8V[4] |
| Astrometry | |
| Radial velocity (Rv) | −30.92±0.20[2] km/s |
| Proper motion (μ) | RA: −60.396 mas/yr[2] Dec.: 48.657 mas/yr[2] |
| Parallax (π) | 15.6253±0.0105 mas[2] |
| Distance | 208.7 ± 0.1 ly (64.00 ± 0.04 pc) |
| Details | |
| Mass | 0.79+0.033 −0.03[5] M☉ |
| Radius | 0.789+0.0064 −0.0056[5] R☉ |
| Temperature | 5357±68[5] K |
| Metallicity [Fe/H] | −0.36±0.05[5] dex |
| Rotational velocity (v sin i) | 1.1 (± 1.1)[6] km/s |
| Age | 7.6+3.4 −3.1[5] Gyr |
| Other designations | |
| KOI-245, KIC 8478994,[3] TYC 3131-1199-1, BD+44 3020, 2MASS J18561431+4431052, GSC 03131-01199, Gaia DR2 2106674071344722688[7] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| KIC | data |
Planetary system
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | <0.79[a] M🜨 | 0.1019±0.0014 | 13.367020(60) | <0.098 | 88.63+0.30 −0.53° |
0.3098+0.0059 −0.0076 R🜨 |
| c | <1.3 M🜨 | 0.1390±0.0020 | 21.301848(18) | <0.099 | 89.07+0.19 −0.33° |
0.755+0.033 −0.055 R🜨 |
| d | <2.0 M🜨 | 0.2109±0.0030 | 39.7922622(65) | <0.10 | 89.335+0.043 −0.047° |
2.030+0.030 −0.039 R🜨 |
| e[13] (disputed) | ≥8.1±1.7 M🜨 | 0.25 | 50.25±0.15 | — | — | ~0.37 R🜨 |
Kepler-37b is the closest planet to Kepler-37. At the time of its discovery in February 2013, it was the smallest known exoplanet.[14] At 3,865 kilometres (2,402 mi) in diameter, it is slightly larger than the Moon.[14] It orbits Kepler-37 once every 13 days at a distance of about 0.1 astronomical units (AU).[6] 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.[14] Surface temperature is estimated at 700 K (427 °C; 800 °F).[12]
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.[6] Neither are able to support liquid water due to their proximity to Kepler-37.[14]
A 2021 study detected Kepler-37d via radial velocity, finding a mass of about 5.4 M🜨,[15] but a 2023 study instead found an upper limit on its mass of only 2 M🜨.[5] In either case, it is not a rocky planet, but a low-density planet rich in volatiles. 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.[16]
Discovery
The Kepler-37 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.[6] Computer simulation was used to rule out other astronomical phenomena mimicking planetary transits with probabilities of error <0.05% (3σ) for each potential planet. Additionally, simulation demonstrated that the proposed planetary configuration was stable.[6] 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.[14]
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.[17] However, he does not anticipate finding many planets as small as Kepler-37b due to the very small amount of light such planets obscure.[17] 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."[12] 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.[17]
The asteroseismology work was, in part, paid for by the Nonprofit Adopt a Star program operated by White Dwarf Research Corporation, a crowd funded non-profit organization.[18]
In 2014, a fourth planet with an orbital period of 51 days (Kepler-37e) was reported based on transit-timing variations.[19] Previously this signal was thought to be a false positive due to its low signal-to-noise ratio, and indeed later studies failed to detect either the transit or TTV signal. A study in 2021 again found that the TTV data disfavors the presence of planet e, and argued that it should be stripped of its "confirmed planet" status.[15]: 3–4, 18–19
A 2023 study modeled the system both with and without a planet candidate at 51 days. Based on the assumption that a planet with a circular orbit of about 51 days is present, marginal radial velocity evidence was found for a sub-Neptune mass planet. Evidence of a longer-period planet candidate was also found. No additional planet has been confirmed, and the system remains with three confirmed planets.[13]: 37–38
Notes
- Masses more than a few times that of the Moon result in unphysically high densities.
