Kepler-37b is an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

(exoplanet) orbiting Kepler-37 in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

Lyra Lyra (; Latin for lyre, from Greek ''λύρα'') is a small constellation. It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union. Lyra ...

. it is the smallest planet discovered around a

main-sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar ...

star, with a radius slightly greater than that of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

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

Kepler-37b is a

sub-Earth A sub-Earth is a planet "substantially less massive" than Earth and Venus. In the Solar System, this category includes Mercury and Mars. Sub-Earth exoplanets are among the most difficult type to detect because their small sizes and masses produ ...

, an exoplanet with a radius and mass smaller than Earth. Its surface temperature is . Because of this, it is not expected to have an atmosphere. Its radius is approximately 0.35 (about a diameter of ), larger than the Moon (0.27 ), but a little smaller than Mercury (0.38 ). Due to its small size, it is very likely Kepler-37b is a

rocky ''Rocky'' is a 1976 American sports drama film directed by John G. Avildsen and written by and starring Sylvester Stallone. It is the first installment in the ''Rocky'' franchise and stars Talia Shire, Burt Young, Carl Weathers, and Burges ...

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 A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

similar to the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, named Kepler-37, orbited by a total of four planets. The star has a mass of 0.80 and a radius of 0.79 . 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 Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

, 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 Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillat ...

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 The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric o ...

, which observes stellar

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

s. 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 Asteroseismology or astroseismology is the study of oscillations in stars. Stars have many resonant modes and frequencies, and the path of sound waves passing through a star depends on the speed of sound, which in turn depends on local temperatur ...

; 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

starThe 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. 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 The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) labo ...

, to conjecture that "such little planets are common".

Notes

References

{{Sky, 18, 56, 14.32, +, 44, 31, 05.3 Exoplanets discovered in 2013 37b Lyra (constellation) Terrestrial planets Transiting exoplanets Kepler-37