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Sub-Earth orbiting Kepler-37, currently the smallest known exoplanet From Wikipedia, the free encyclopedia
Kepler-37b is an exoplanet orbiting the star Kepler-37 in the constellation Lyra.[3] 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.[4] 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[1] | |
|---|---|
| Discovery site | Kepler space telescope |
| Discovery date | February 20, 2013 |
| Transit | |
| Orbital characteristics[2] | |
| 0.1019±0.0014 AU | |
| Eccentricity | <0.098 |
| 13.367020(60) d | |
| Inclination | 88.63°+0.30° −0.53° |
| Star | Kepler-37 |
| Physical characteristics[2] | |
| 0.3098+0.0059 −0.0076 R🜨 | |
| Mass | <0.79 M🜨[lower-alpha 1] |
| Temperature | 718±10 K (445 °C; 833 °F, equilibrium) |
| 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).[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]
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.[citation needed]
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.
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]
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