Kepler-37b

Kepler-37b is an extrasolar planet (exoplanet) orbiting Kepler-37 in the constellation Lyra.[7] 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.[8] 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
Discovery site	Kepler Space Observatory
Discovery date	February 20, 2013[1]
Detection method	Transit (Kepler Mission)
Orbital characteristics
Semi-major axis	0.1003 AU (15,000,000 km)[2]
Eccentricity	0.080^+0.210 −0.080
Orbital period	13.367308[1] d
Inclination	88.63[2]
Star	Kepler-37
Physical characteristics
Mean radius	0.354 (± 0.014) R⊕
Mass	0.01^+5.99 −0.01[3][4][5][lower-alpha 1] M⊕
Temperature	700 K (427 °C; 800 °F)[6]

Characteristics

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

Mass, radius and temperature

Kepler-37b is a sub-Earth, an exoplanet with a radius and mass smaller than Earth. Its surface temperature is 700 K (427 °C; 800 °F). Because of this, it is not expected to have an atmosphere.[6] Its radius is approximately 0.35 R_⊕ (about a diameter of 3,900 kilometres (2,400 mi)), larger than the Moon[9] (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[10] and has a temperature of 5778 K.[11]

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).[8] The outer two planets in the system have orbital periods[1][2] 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;[9] 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.[8] 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.[12] 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

• List of exoplanet extremes

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.
2. "Kepler-37 System". kepler.nasa.gov. Retrieved February 21, 2013.
3. Johnson, Michele (31 March 2015). "Kepler and K2 Missions". nasa.gov. Retrieved 5 October 2017.
4. "Archived copy". Archived from the original on 2014-02-09. Retrieved 2014-03-03.CS1 maint: archived copy as title (link)
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 Smallkeplerplanets: The Transition from Gaseous to Rocky Planets". The Astrophysical Journal Supplement Series. 210 (2): 20. arXiv:1401.4195. doi:10.1088/0067-0049/210/2/20.
6. "NASA's Kepler Mission Discovers Tiny Planet System". NASA. February 20, 2013. Retrieved February 21, 2013.
7. "Smallest Alien Planet Kepler-37b Explained (Infographic)". space.com. Retrieved 5 October 2017.
8. "Tiniest Planet Yet Discovered by NASA Outside our Solar System". scienceworldreport.com. February 21, 2013. Retrieved February 21, 2013.
9. "Astronomers Find the Tiniest Exoplanet Yet". Slate. February 20, 2013. Retrieved February 21, 2013.
10. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
11. Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
12. "Small Planets Confirm Kepler's Capabilities". www.centauri-dreams.org. Retrieved 5 October 2017.

Records
Preceded by PSR B1257+12 A	Least massive exoplanet 2013—	Succeeded by current
Preceded by Kepler-42 d	Smallest-radius exoplanet 2013—	Succeeded by current