Kepler-39b (formerly known as KOI-423b), is a confirmed

extrasolar object An extrasolar object () is an astronomical object that exists outside the Solar System. It is not applied to stars, or any other celestial object that is larger than a star or the Solar System, such as a galaxy. The terms for extrasolar example ...

(either a Jovian planet or

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

because of its mass) discovered orbiting the F-type star Kepler-39. It is eighteen times more massive than Jupiter, and is about five fourths its size. The planet orbits its host star at about 15% of the average distance between the Earth and Sun. Kepler-39b's host star was investigated by European astronomers along with three other stars, including the host star of Kepler-40b, using equipment at the

Haute-Provence Observatory The Haute-Provence Observatory (OHP, ) is an astronomical observatory in the southeast of France, about 90 km east of Avignon and 100 km north of Marseille. It was established in 1937 as a national facility for French astronomers. Ast ...

in France. Collection and analysis of data in late 2010 led to the confirmation of Kepler-39b. The discovery paper was published in a journal on June 6, 2011. The location of the

subgiant star A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the object is compared to the celestial equator and is expressed in degrees. For Kepler-39, the location is 19h 47m 50.00 and 46° 02` 04.00 .

Characteristics

Mass, radius, and temperature

Kepler-39b is a Jupiter-like planet or brown dwarf that is eighteen times more massive than Jupiter and 1.22 times Jupiter's size. For a planet of its size, Kepler-39b has a relatively cool

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, th ...

of with respect to other inflated planets, defying most of the common models explaining inflation at the time of its discovery (including

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

and the effect of stellar radiation). Although Kepler-39b and

COROT-3b CoRoT-3b (formerly known as CoRoT-Exo-3b) is a brown dwarf or massive extrasolar planet with a mass 21.66 times that of Jupiter. The object orbits the stellar classification, F-type star CoRoT-3 in the constellation of Aquila (constellati ...

have similar characteristics (in terms of host star and mass), COROT-3b lies on the predicted size of what a planet of its character should look like. Kepler-39b is far larger than this model. A recent study reveals that Kepler-39b probably has a shape that is very oblate, which, if true, is very likely caused by its fast rotation. The estimated rotation period would be about 1.6 hours, very fast compared to about 10 hours for Jupiter and Saturn. Such a fast rotation also provides a natural explanation for its large radius. In 2022, the radius of Kepler-39b was improved based on direct

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measaurements by the

Gaia spacecraft ''Gaia'' was a space observatory of the European Space Agency (ESA) that was launched in 2013 and operated until March 2025. The spacecraft was designed for astrometry: measuring the positions, distances and motions of stars with unprecedented ...

, which allows the distance to the host star to be known. The newly-determined radius of is slightly lower than the previous estimate of .

Host star

Kepler-39 is an

F-type F-type may refer to: *F-type asteroid, a type of carbonaceous asteroid *F-ATPase, a membrane protein *F-type main-sequence star, a hydrogen-fusing star * F-type Prisons, high-security prisons in Turkey *MG F-type Magna, six-cylinder-engined car pr ...

star that is slightly larger and slightly more massive than the Sun (respectively, 1.10

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es and 1.39

solar radii Solar may refer to: Astronomy * Of or relating to the Sun ** Solar telescope, a special purpose telescope used to observe the Sun ** A device that utilizes solar energy (e.g. "solar panels") ** Solar calendar, a calendar whose dates indicat ...

) that is located 1090

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s (3,560

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s) away from Earth. With an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 6260 K, Kepler-39 is hotter than the Sun. Kepler-39 is significantly metal-poor, reflected in its

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

of e/H= -0.29 (51% the amount of iron found in the Sun). Kepler-39 has an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 14.3, and is thus not visible with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

from Earth.

Orbital statistics

The planet orbits at a distance of 0.155 AU, equating to roughly 15% of the average distance between the Earth and Sun, completing one orbit every 21.0874 days. Kepler-39b has a modestly elliptical orbit, as described by its

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

of 0.121. Its

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

is 88.83º, making the planet appear almost entirely edge-on to its host star as seen from Earth.

Discovery

The

Kepler Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of p ...

spacecraft is a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

telescope equipped with photometric equipment. Launched in 2009, Kepler continuously watches 156,000 stars in a small area. A team of astronomers, hoping to learn more about

hot jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...

planets and

s, selected four F-type stars from the

Kepler Input Catalog The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program (SCP) and the Kepler space telescope. Overview The Kepler SCP targets were observed by t ...

flagged as host to a Kepler Object of Interest (a transiting object that could possibly be a planet). Using three quarters of Kepler's data, the science team conducted a follow-up investigation in using the

SOPHIE échelle spectrograph Sophie is a feminine given name, another version of Sophia, from the Greek word for "wisdom". People with the name Born in the Middle Ages * Sophie, Countess of Bar (c. 1004 or 1018–1093), sovereign Countess of Bar and lady of Mousson * Sop ...

at the

in southern France, observing stars Kepler-40, Kepler-39, KOI-552 and KOI-410. Of these, conclusive evidence of a planet orbiting KOI-410 could not be found, and KOI-552 was found to be a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

with an M-type companion. The

Hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...

KOI-428b was the first of these four to be confirmed. SOPHIE collected thirteen

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

measurements of Kepler-39 between July 26, 2010 and September 10, 2010. Seven of the measurements were affected by moonlight, but were corrected. These radial velocity measurements conclusively eliminated the possibility that the observed dips in Kepler-39's brightness were caused by the movements of binary stars and confirming the existence of planet Kepler-39b in the process. SOPHIE's measurements were used to derive Kepler-39's

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

, which was used to define Kepler-39b's characteristics. The astronomers submitted the discovery paper to ''

Astronomy and Astrophysics ''Astronomy & Astrophysics (A&A)'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. It is operated by an editorial team under the supervision of a board of directors re ...

'' on June 16, 2011 with François Bouchy as the leading author. The discovery paper covered the investigations of KOI-410 and KOI-552 along with the discovery of Kepler-39b.

References

{{2011 in space Giant planets Exoplanets discovered in 2011 Transiting exoplanets 39b Cygnus (constellation)