Kepler-37b

Kepler-37b is an exoplanet orbiting the star Kepler-37 in the constellation Lyra.[3] As of February 2013 it is the smallest planet discovered around a main-sequence star, with a radius slightly greater than that of the Moon and slightly smaller than that of Mercury.[4] The measurements do not constrain its mass, but masses above a few times that of the Moon give unphysically high densities.[5]

Kepler-37b
Artist's impression of Kepler-37b.
Discovery[1]
Discovery siteKepler space telescope
Discovery dateFebruary 20, 2013
Transit
Orbital characteristics[2]
0.1019±0.0014 AU
Eccentricity<0.098
13.367020(60) d
Inclination88.63°+0.30°
−0.53°
StarKepler-37
Physical characteristics[2]
Mean radius
0.3098+0.0059
−0.0076 R🜨
Mass<0.79 M🜨[lower-alpha 1]
Temperature718±10 K (445 °C; 833 °F, equilibrium)

    Characteristics
    A size comparison of the planets in the Kepler-37 system and objects in the Solar System

    Mass, radius and temperature
    Size comparison
    Earth Kepler-37
    Exoplanet

    Kepler-37b is a sub-Earth, an exoplanet with a radius and mass smaller than Earth. Its equilibrium temperature is 718 K (445 °C; 833 °F).[2] Because of its small size, it is not expected to have an atmosphere.[6] Its radius is approximately 0.31 R🜨 (about 1,980 kilometres (1,230 mi)),[2] slightly larger than the Moon[7] (0.27 R🜨), but a little smaller than Mercury (0.38 R🜨). Due to its small size, it is very likely Kepler-37b is a rocky planet with a solid surface.[6] Furthermore, it is too hot to support liquid water on its surface.[6]

    Host star

    The planet orbits a (G-type) star similar to the Sun, named Kepler-37, orbited by a total of four planets. The star has a mass of 0.80 M☉ and a radius of 0.79 R☉. It has a temperature of 5417 K and is 5.66 billion years old. In comparison, the Sun is 4.6 billion years old[8] and has a temperature of 5778 K.[9]

    The star's apparent magnitude, or how bright it appears from Earth's perspective, is 9.71. Therefore, it is too dim to be seen with the naked eye.

    Orbit

    Kepler-37b orbits its parent star at a distance of about 15 million kilometers (9.3 million miles), with a period of roughly 13 days at a distance of 0.1 AU (compared to Mercury's distance from the Sun, which is about 0.38 AU).[4] The outer two planets in the system have orbital periods[1][10] within one percent of the 8:5 and 3:1 resonances with Kepler-37b's period.

    Discovery

    Kepler-37b, along with two other planets, Kepler-37c and Kepler-37d, were discovered by the Kepler space telescope, which observes stellar transits.[1][6] After observing transits of Kepler-37b, astronomers had to compare it with the size of the parent star.

    The size of the star was obtained using asteroseismology;[7] Kepler-37 is currently the smallest star to be studied using this process.[6] This allowed the size of Kepler-37b to be determined "with extreme accuracy".[6]

    To date, Kepler-37b is the smallest planet discovered around a main-sequence star[lower-alpha 2] outside the Solar System.[4] Detection of Kepler-37b was possible due to its short orbital period, relative brightness, and low activity of its host star, allowing brightness data to average out quickly.[11] The discovery of Kepler-37b has led Jack Lissauer, a scientist at NASA's Ames Research Center, to conjecture that "such little planets are common".[6]

    See also

    Notes
    1. Masses more than a few times that of the Moon result in unphysically high densities.
    2. The pulsar planet PSR B1257+12 A has a comparable mass. The actual size of PSR B1257+12 A is unknown, but is likely comparable to Kepler-37b.

    References
    1. Barclay, T.; Rowe, J. F.; Lissauer, J. J.; Huber, D.; Fressin, F.; Howell, S. B.; Bryson, S. T.; Chaplin, W. J.; Désert, J. M. (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.
    2. Bonomo, A. S.; Dumusque, X.; 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. arXiv:2304.05773. doi:10.1051/0004-6361/202346211. S2CID 258078829.
    3. "Smallest Alien Planet Kepler-37b Explained (Infographic)". space.com. 20 February 2013. Retrieved 5 October 2017.
    4. "Tiniest Planet Yet Discovered by NASA Outside our Solar System". scienceworldreport.com. February 21, 2013. Retrieved February 21, 2013.
    5. Marcy, Geoffrey W.; Isaacson, Howard; Howard, Andrew W.; Rowe, Jason F.; Jenkins, Jon M.; Bryson, Stephen T.; Latham, David W.; Howell, Steve B.; Gautier, Thomas N.; Batalha, Natalie M.; Rogers, Leslie; Ciardi, David; Fischer, Debra A.; Gilliland, Ronald L.; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Huber, Daniel; Chaplin, William J.; Basu, Sarbani; Buchhave, Lars A.; Quinn, Samuel N.; Borucki, William J.; Koch, David G.; Hunter, Roger; Caldwell, Douglas A.; Van Cleve, Jeffrey; Kolbl, Rea; Weiss, Lauren M.; Petigura, Erik; et al. (2014). "Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets". The Astrophysical Journal Supplement Series. 210 (2): 20. arXiv:1401.4195. Bibcode:2014ApJS..210...20M. doi:10.1088/0067-0049/210/2/20. S2CID 10760418.
    6. "NASA's Kepler Mission Discovers Tiny Planet System". NASA. February 20, 2013. Retrieved February 21, 2013.
    7. "Astronomers Find the Tiniest Exoplanet Yet". Slate. February 20, 2013. Retrieved February 21, 2013.
    8. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
    9. Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
    10. "Kepler-37 System". kepler.nasa.gov. Archived from the original on May 16, 2013. Retrieved February 21, 2013.
    11. "Small Planets Confirm Kepler's Capabilities". www.centauri-dreams.org. Retrieved 5 October 2017.
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