Astronomy:Kepler-37

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Short description: G-type main-sequence star in the constellation Lyra

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

Kepler-37
A Moon-size Line Up.jpg
Line up comparing the planets in the Kepler-37 system to the Moon and planets in the Solar System.
Observation data
Equinox J2000.0]] (ICRS)
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[1] mas/yr
Dec.: 48.657[1] mas/yr
Parallax (π)15.6253 ± 0.0105[1] mas
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
Extrasolar Planets
Encyclopaedia
data
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

The Kepler-37 planetary system[4][3]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
Eccentricity Inclination Radius
b <0.79[lower-alpha 1] 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 5.4±1.4[11] M 0.2109±0.0030 39.7922622(65) <0.10 89.335+0.043
−0.047
°
2.030+0.030
−0.039
 R
e (dubious) 0.2508 51.196

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 M,[11] but a 2023 study instead found an upper limit on its mass of only 2 M.[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.[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.[4] 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.[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.[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 the Nonprofit Adopt a Star program operated by White Dwarf Research Corporation, a crowd funded non-profit organization.[15]

In 2014, a fourth planet with orbital period of 51 days (Kepler-37e) was reported based on transit-timing variations.[16] 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.[11]

Notes

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

References

  1. 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. 2.0 2.1 "Kepler Host Star Characteristics". Archive for Space Telescopes. STSI. 2012-02-24. https://archive.stsci.edu/kepler/host_stars.html. 
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Bonomo, A. S. et al. (April 2023). "Cold Jupiters and improved masses in 38 Kepler and K2 small-planet systems from 3661 high-precision HARPS-N radial velocities. No excess of cold Jupiters in small-planet systems". Astronomy & Astrophysics. doi:10.1051/0004-6361/202346211. 
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Barclay, T.; Rowe, J. F.; Lissauer, J. J.; Huber, D.; Fressin, F.; Howell, S. B.; Bryson, S. T.; Chaplin, W. J. et al. (2013-02-20). "A sub-Mercury-sized exoplanet". Nature 494 (7438): 452–4. doi:10.1038/nature11914. ISSN 0028-0836. PMID 23426260. Bibcode2013Natur.494..452B. 
  5. "TYC 3131-1199-1". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=TYC+3131-1199-1. 
  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. 10.0 10.1 10.2 "NASA's Kepler Mission Discovers Tiny Planet System" (Press release). NASA. February 20, 2012. Retrieved February 21, 2012.
  11. 11.0 11.1 11.2 Rajpaul, V. M.; Buchhave, L. A.; Lacedelli, G.; Rice, K.; Mortier, A.; Malavolta, L.; Aigrain, S.; Borsato, L. et al. (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, doi:10.1093/mnras/stab2192, Bibcode2021MNRAS.507.1847R  Kepler-37e is discussed in sections 2.2.2 & 6.4.
  12. 12.0 12.1 12.2 12.3 12.4 Catherine Griffin (February 21, 2013). "Tiniest Planet Yet Discovered by NASA Outside our Solar System". Science World Report. http://www.scienceworldreport.com/articles/5098/20130221/tiniest-planet-discovered-nasa-outside-solar-system.htm. 
  13. "Tompkins County Strategic Tourism Planning Board". April 15, 2015. http://www.tompkinscountyny.gov/files/tourism/4_15_15_STPB_agenda_PACKET_full.pdf. 
  14. 14.0 14.1 14.2 Eryn Brown (February 21, 2013). "NASA, using Kepler space telescope, finds smallest planet yet". LA Times. http://www.latimes.com/news/science/la-sci-small-exoplanet-20130221,0,4749761.story. 
  15. Phil Plait (February 20, 2013). "Astronomers Find the Tiniest Exoplanet Yet". Bad Astronomy blog (Slate). http://www.slate.com/blogs/bad_astronomy/2013/02/20/smallest_exoplanet_kepler_37b_is_barely_bigger_than_earth_s_moon.html. 
  16. Hadden, Sam; Lithwick, Yoram (2014). "Densities and Eccentricities of 139 Kepler Planets from Transit Time Variations". The Astrophysical Journal 787 (1): 80. doi:10.1088/0004-637X/787/1/80. Bibcode2014ApJ...787...80H. 

Further reading

External links