Kepler-37b is an extrasolar planet (exoplanet) orbiting Kepler-37 in the constellation Lyra.[7] As of February 2013[update] 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. [8] The measurements do not constrain its mass, but masses above a few times that of the Moon give unphysically high densities.[5]
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 (sidereal) | 13.367308[1] d |
| Inclination | 88.63[2] |
| Star | Kepler-37 |
| Physical characteristics | |
Mean radius | 0.354 (± 0.014) REarth |
| Mass | 0.01+5.99 −0.01[3][4][5][lower-alpha 1] MEarth |
| Temperature | 700 K (427 °C; 800 °F)[6] |

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 REarth (about a diameter of 3,900 kilometres (2,400 mi)), larger than the Moon[9] (0.27 REarth), but a little smaller than Mercury (0.38 REarth). 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]
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.
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.
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]
| Records | ||
|---|---|---|
| Preceded by | Least massive exoplanet[citation needed] 2013—2015 |
Succeeded by |
| Preceded by Kepler-42 d |
Smallest-radius exoplanet 2013—2015 |
Succeeded by |
The Kepler-37 system | |
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