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Kepler-37b

Artist's impression of Kepler-37b.
Discovery
Discovery site	Kepler space telescope
Discovery date	February 20, 2013
Detection method	Transit
Orbital characteristics
Semi-major axis	0.1019±0.0014 AU
Eccentricity	<0.098
Orbital period (sidereal)	13.367020(60) d
Inclination	88.63°+0.30° −0.53°
Star	Kepler-37
Physical characteristics
Mean radius	0.3098+0.0059 −0.0076 R🜨
Mass	<0.79 M🜨
Temperature	718±10 K (445 °C; 833 °F, equilibrium)

Kepler-37b is an exoplanet orbiting the star Kepler-37 in the constellation Lyra. 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. The measurements do not constrain its mass, but masses above a few times that of the Moon give unphysically high densities.

Characteristics

Mass, radius and temperature

Size comparison

Earth	Kepler-37b

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). Because of its small size, it is not expected to have an atmosphere. Its radius is approximately 0.31 R_🜨 (about 1,980 kilometres (1,230 mi)), slightly larger than the Moon (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. Furthermore, it is too hot to support liquid water on its surface.

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, and has a temperature of 5778 K.

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). The outer two planets in the system have orbital periods 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. 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; Kepler-37 is currently the smallest star to be studied using this process. This allowed the size of Kepler-37b to be determined "with extreme accuracy".

To date, Kepler-37b is the smallest planet discovered around a main-sequence star outside the Solar System. 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. 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".

See also

• List of exoplanet extremes
• List of smallest exoplanets

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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