Kepler-37

Kepler-37

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
Right ascension 18h 56m 14.30760s[1]
Declination +44° 31′ 05.3896″[1]
Apparent magnitude (V) 9.710[2]
Characteristics
Spectral type G8V
Astrometry
Radial velocity (Rv)−30.92±0.20[1] km/s
Proper motion (μ) RA: −60.396 mas/yr[1]
Dec.: 48.657 mas/yr[1]
Parallax (π)15.6253 ± 0.0105 mas[1]
Distance208.7 ± 0.1 ly
(64.00 ± 0.04 pc)
Details
Mass0.79+0.033
−0.03[3] M☉
Radius0.789+0.0064
−0.0056[3] R☉
Temperature5357±68[3] K
Metallicity [Fe/H]−0.36±0.05[3] dex
Rotational velocity (v sin i)1.1 (± 1.1)[4] km/s
Age7.6+3.4
−3.1[3] Gyr
Other designations
KOI-245, KIC 8478994,[2] TYC 3131-1199-1, BD+44 3020, 2MASS J18561431+4431052, GSC 03131-01199, Gaia DR2 2106674071344722688[5]
Database references
SIMBADdata
KICdata

Kepler-37, also known as UGA-1785,[6][7][8] 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.[4] 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,[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

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The Kepler-37 planetary system[3]
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[11] (disputed) ≥8.1±1.7 M🜨 0.25 50.25±0.15 — — —

Kepler-37b is the closest planet to 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).[4] 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.[4] Neither are able to support liquid water due to their proximity to Kepler-37.[12]

A 2021 study detected Kepler-37d via radial velocity, finding a mass of about 5.4 ME,[13] but a 2023 study instead found an upper limit on its mass of only 2 ME.[3] 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.[14]

Discovery

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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.[4] 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.[4] 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.[15] However, he does not anticipate finding many planets as small as Kepler-37b due to the very small amount of light such planets obscure.[15] 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.[15]

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.[16]

In 2014, a fourth planet with an orbital period of 51 days (Kepler-37e) was reported based on transit-timing variations.[17] 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.[13]: 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.[11]: 37–38 

Notes

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

References

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  1. ^ a b c d e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  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 f g Bonomo, A. S.; Dumusque, X.; et al. (September 2023). "Cold Jupiters and improved masses in 38 Kepler and K2 small planet systems from 3661 HARPS-N radial velocities. No excess of cold Jupiters in small planet systems". Astronomy & Astrophysics. 677: A33. arXiv:2304.05773. Bibcode:2023A&A...677A..33B. doi:10.1051/0004-6361/202346211. S2CID 258078829.
  4. ^ 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. S2CID 205232792.
  5. ^ "TYC 3131-1199-1". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2013-02-22.
  6. ^ Planets in Kepler-37 star system designated ‘UGA-1785’ by NASA
  7. ^ 211 light years away, star system named for UGA
  8. ^ Kepler-37, Open Exoplanet catalogue
  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 Weiss, Lauren M.; et al. (2024-01-01). "The Kepler Giant Planet Search. I. A Decade of Kepler Planet-host Radial Velocities from W. M. Keck Observatory". The Astrophysical Journal Supplement Series. 270 (1) 8. arXiv:2304.00071. Bibcode:2024ApJS..270....8W. doi:10.3847/1538-4365/ad0cab.
  12. ^ 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.
  13. ^ a b Rajpaul, V. M.; Buchhave, L. A.; Lacedelli, G.; Rice, K.; Mortier, A.; Malavolta, L.; Aigrain, S.; Borsato, L.; Mayo, A. W.; Charbonneau, D.; Damasso, M.; Dumusque, X.; Ghedina, A.; Latham, D. W.; López-Morales, M.; Magazzù, A.; Micela, G.; Molinari, E.; Pepe, F.; Piotto, G.; Poretti, E.; Rowther, S.; Sozzetti, A.; Udry, S.; Watson, C. A. (2021), "A HARPS-N mass for the elusive Kepler-37d: A case study in disentangling stellar activity and planetary signals", Monthly Notices of the Royal Astronomical Society, 507 (2): 1847–1868, arXiv:2107.13900, Bibcode:2021MNRAS.507.1847R, doi:10.1093/mnras/stab2192
  14. ^ "Tompkins County Strategic Tourism Planning Board" (PDF). Tompkins County NY. April 15, 2015. Archived from the original (PDF) on December 27, 2016. Retrieved March 5, 2016.
  15. ^ a b c Eryn Brown (February 21, 2013). "NASA, using Kepler space telescope, finds smallest planet yet". LA Times. Retrieved February 21, 2013.
  16. ^ Phil Plait (February 20, 2013). "Astronomers Find the Tiniest Exoplanet Yet". Bad Astronomy blog. Slate. Retrieved February 21, 2013.
  17. ^ Hadden, Sam; Lithwick, Yoram (2014). "Densities and Eccentricities of 139 Kepler Planets from Transit Time Variations". The Astrophysical Journal. 787 (1): 80. arXiv:1310.7942. Bibcode:2014ApJ...787...80H. doi:10.1088/0004-637X/787/1/80. S2CID 119097836.

Further reading

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