Astronomy:Kepler-37

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Kepler-37, also known as UGA-1785,[1][2][3] 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,[5] 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.[6]

Planetary system

The Kepler-37 planetary system[7]
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 <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[8] (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.[9] At 3,865 kilometres (2,402 mi) in diameter, it is slightly larger than the Moon.[9] 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.[9] Surface temperature is estimated at 700 K (427 °C; 800 °F).[6]

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.[9]

A 2021 study detected Kepler-37d via radial velocity, finding a mass of about 5.4 M⊕,[10] but a 2023 study instead found an upper limit on its mass of only 2 M⊕.[7] 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.[11]

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.[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.[9]

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."[6] 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 the Nonprofit Adopt a Star program operated by White Dwarf Research Corporation, a crowd funded non-profit organization.[13]

In 2014, a fourth planet with an orbital period of 51 days (Kepler-37e) was reported based on transit-timing variations.[14] 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.[10]: 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.[8]: 37–38 

Notes

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

References

  1. ↑ Planets in Kepler-37 star system designated ‘UGA-1785’ by NASA
  2. ↑ 211 light years away, star system named for UGA
  3. ↑ Kepler-37, Open Exoplanet catalogue
  4. ↑ 4.0 4.1 4.2 4.3 4.4 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. Bibcode: 2013Natur.494..452B. 
  5. ↑ Smallest Alien Planet Kepler-37b Explained (Infographic)
  6. ↑ 6.0 6.1 6.2 "NASA's Kepler Mission Discovers Tiny Planet System" (Press release). NASA. February 20, 2012. Archived from the original on September 8, 2018. Retrieved February 21, 2012.
  7. ↑ 7.0 7.1 Bonomo, A. S. 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. doi:10.1051/0004-6361/202346211. Bibcode: 2023A&A...677A..33B. 
  8. ↑ 8.0 8.1 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). doi:10.3847/1538-4365/ad0cab. Bibcode: 2024ApJS..270....8W. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 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. 
  10. ↑ 10.0 10.1 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, Bibcode: 2021MNRAS.507.1847R 
  11. ↑ "Tompkins County Strategic Tourism Planning Board". April 15, 2015. http://www.tompkinscountyny.gov/files/tourism/4_15_15_STPB_agenda_PACKET_full.pdf. 
  12. ↑ 12.0 12.1 12.2 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. 
  13. ↑ 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. 
  14. ↑ 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. Bibcode: 2014ApJ...787...80H. 

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Further reading



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