42 Draconis (abbreviated 42 Dra), formally named Fafnir ( or ), is a 5th

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

K-type

giant In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

located approximately 295

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

s away in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Draco. An

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

(designated 42 Draconis b, later named Orbitar) was once thought to be orbiting the star, but its existence has since been refuted. Of

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

K1.5III, the star has a mass similar to the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

but with a radius 22 times greater. It is a metal-poor star with metallicity as low as 35% that of the Sun and its age is 9.49 billion years. It is the southern

pole star A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles. On Earth, a pole star would lie directly overhead when ...

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

. A 2019 study using

Gaia DR2 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia (spacecraft), Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also mis ...

data found a companion star to 42 Draconis, about half the Sun's mass, at a separation of 24

arcsecond A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s, corresponding to 2220 AU.

Nomenclature

42 Draconis is the star's

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the 88 modern constellations, modern constellations visible from southern England. They are named after John Flamsteed, au ...

. Following its discovery the planet was designated 42 Draconis b. In July 2014 the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

launched

NameExoWorlds NameExoWorlds (also known as IAU NameExoWorlds) were various projects managed by the International Astronomical Union (I.A.U.) to encourage names to be submitted for astronomical objects, notably exoplanets. The accepted names would later be cons ...

, a process for giving proper names to certain exoplanets and their host stars. The process involved public nomination and voting for the new names. In December 2015, the IAU announced the winning names were Fafnir for this star and Orbitar for its planet. The winning names were submitted by the Brevard Astronomical Society of

Brevard County, Florida Brevard County ( ) is a county in the U.S. state of Florida. It is on the Atlantic coast of eastern Central Florida. As of the 2020 census, the population was 606,612, making it the 10th-most populated county in Florida. The official county s ...

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. Fafnir was a Norse mythological dwarf who turned into a dragon, it is also the name of a fictional planet in

Larry Niven Laurence van Cott Niven (; born April 30, 1938) is an American science fiction writer. His 1970 novel ''Ringworld'' won the Hugo Award for Best Novel, Hugo, Locus Award, Locus, Ditmar Award, Ditmar, and Nebula Award for Best Novel, Nebula award ...

Known Space Known Space is the fictional setting of about a dozen science fiction novels and several collections of short stories by American writer Larry Niven. It has also become a shared universe in the spin-off ''Man-Kzin Wars'' anthologies. The Inter ...

universe of similar description, ('Draco' is

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for 'dragon'); Orbitar is a contrived word paying homage to the space launch and orbital operations of

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 ...

. In 2016, the IAU organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. In its first bulletin of July 2016, the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.

Disproven planet

The discovery of 42 Draconis b (later named Orbitar) by the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in th ...

was announced in 2009. It was thought to be a

super-Jupiter A super-Jupiter is a gas giant exoplanet that is more massive than the planet Jupiter. For example, substellar companion, companions at the planet–brown dwarf borderline have been called super-Jupiters, such as around the star Kappa Andromedae. ...

, with a

minimum mass In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars, binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets detected by the radial velocit ...

4 times that of Jupiter, an orbital period of 479 days, and an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.38. However, the existence of this planet was questioned in a 2021 study by the same authors, which found that more recent radial velocity measurements were inconsistent with the proposed planetary orbit. With further observations, by 2025 the planet hypothesis could be conclusively ruled out. The star appears to have intrinsic radial velocity variations that mimic a planetary companion, as observed in other giant stars such as

Gamma Draconis Gamma Draconis (γ Draconis, abbreviated Gamma Dra, γ Dra), formally named Eltanin , is a star in the northern constellation of Draco. Contrary to its gamma-designation (historically third-ranked), it is the brightest object in Draco a ...

and

Aldebaran Aldebaran () is a star in the zodiac constellation of Taurus. It has the Bayer designation α Tauri, which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Aldebaran varies in brightness from an apparent vis ...

. In a 2024 study, 42 Draconis b was listed as one of several doubtful planets around giant stars, along with other named planets around

14 Andromedae 14 Andromedae, abbreviated 14 And, also named Veritate , is a single, orange-hued giant star situated 248 light-years away in the northern constellation of Andromeda. It is dimly visible to the naked eye with an apparent visual magnitude ...

and 41 Lyncis. With the 2025 refutation, it is now the second named exoplanet to be conclusively disproven, after

Fomalhaut b TW Piscis Austrini (also known as Fomalhaut B) is a main sequence star in the constellation Piscis Austrinus. It lies relatively close to the Sun, at an estimated distance of . To an observer on Earth the star is visually separated from i ...

(Dagon) in 2020.

References

External links

* K-type giants Draconis, 42 170693 090344 6945 Draco (constellation) Hypothetical planetary systems BD+65 1271 Fafnir {{exoplanet-stub

Nomenclature

Disproven planet

See also

References

External links