Upsilon Andromedae c (υ Andromedae c, abbreviated Upsilon And c, υ And c), formally named Samh (a homophone with the star Salm), is an

extrasolar planet 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 detect ...

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

ing 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 ...

-like

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 ...

Upsilon Andromedae A every 241.3 days at an average distance of . Its discovery in April 1999 by

Geoffrey Marcy Geoffrey William Marcy (born September 29, 1954) is an American astronomer. He was an early influence in the field of exoplanet detection, discovery, and characterization. Marcy was a professor of astronomy at the University of California, Berke ...

and R. Paul Butler made this the first multiple- planet system to be discovered around a

main-sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of star ...

star, and the first multiple-planet system known in a

multiple star A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...

system. Upsilon Andromedae c is the second-known planet in order of distance from its star.

Name

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 name was Samh for this planet. The winning name was submitted by the Vega Astronomy Club of

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

and honours the 11th-century astronomer Ibn al-Samh of

Muslim Spain Al-Andalus () was the Muslim-ruled area of the Iberian Peninsula. The name refers to the different Muslim states that controlled these territories at various times between 711 and 1492. At its greatest geographical extent, it occupied most o ...

Discovery

Upsilon Andromedae c was detected by measuring variations in its star's

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 ...

as a result of the planet's

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

. This was done by making precise measurements of the

Doppler shift The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...

of the

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 ...

of Upsilon Andromedae A. At the time of discovery, Upsilon Andromedae A was already known to host one extrasolar planet, 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 ...

Upsilon Andromedae b Upsilon Andromedae b (υ Andromedae b, abbreviated Upsilon And b, υ And b), formally named Saffar , is an extrasolar planet approximately 44 light-years away from the Sun in the constellation of Andromeda (constellation), Andromeda. The planet o ...

; however, by 1999 it was clear that the inner planet could not explain the velocity curve. In 1999, astronomers at both

San Francisco State University San Francisco State University (San Francisco State, SF State and SFSU) is a Public university, public research university in San Francisco, California, United States. It was established in 1899 as the San Francisco State Normal School and is ...

and the Harvard-Smithsonian Center for Astrophysics independently concluded that a three-planet model best fit the data. The two new planets were designated Upsilon Andromedae c and

Upsilon Andromedae d Upsilon Andromedae d (υ Andromedae d, abbreviated Upsilon And d, υ And d), formally named Majriti , is a super-Jupiter exoplanet orbiting within the habitable zone of the Sun-like star Upsilon Andromedae A, approximately 44 light-years (13.5 p ...

Host star

The planet orbits a (

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 ...

)

named Upsilon Andromedae A. The star has a mass of 1.27 and a radius of around 1.48 . It has a temperature of 6,074 K and is 3.12 billion years old. In comparison, the Sun is about 4.6 billion years old. The star is slightly metal-rich, with a

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 ...

( e/H of 0.09, or about 123% of the solar amount. Its luminosity () is 3.57 times that of the Sun. The star's

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), ...

, or how bright it appears from Earth's perspective, is 4.09. Therefore, Upsilon Andromedae can be seen with the naked eye.

Orbit and mass

Like the majority of long-

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

extrasolar planets, the orbit of Upsilon Andromedae c is eccentric, more so than any of the major planets in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

(including

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

). If placed in the Solar System, Upsilon Andromedae c would lie between the orbits of Earth and

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 ...

. The high orbital eccentricity may be the result of

gravitational In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force be ...

perturbations from the planet Upsilon Andromedae d. Simulations suggest that the orbit of Upsilon Andromedae c returns to its original circular state roughly once every 9,000 years. One proposal is that interactions between Upsilon Andromedae d and a (now lost) outer planet moved Upsilon Andromedae d into an orbit closer to the star, where it gradually caused the orbit of Upsilon Andromedae c to become eccentric. If so, the rogue planet would have had to eject immediately. A limitation of the radial velocity method used to detect Upsilon Andromedae c is that the orbital inclination is unknown, and only a lower limit on the planet's

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

can be obtained. Because the planet's orbit is inclined by only about 8 degrees from the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

, the radial velocity signal is comparatively weak, and c was consequently thought at first to have a mass closer to only 2 Jupiter masses. However, subsequently astrometry was used to ascertain the planet's true mass; by combining radial velocity measurements from ground-based telescopes with astrometric data from the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

, astronomers have determined the orbital inclination as well as the actual

of Upsilon Andromedae c, which is about 13.98 times the mass of

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

. The mutual

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 Eart ...

between c and d is 29.9 degrees.

Characteristics

Given the planet's high mass, it is likely that Upsilon Andromedae c is a

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...

with no solid surface. Since the planet has only been detected indirectly through observations of its star, properties such as its

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

, composition, and

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

are unknown. Since its actual mass is approximately 14 times that of Jupiter, and its star's metallicity is similar to that of the Sun, Upsilon Andromedae c may actually be a small

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 ...

, but this may not be the case. Deuterium burning, which by some criteria defines brown dwarf status, can occur in bodies larger than about 13 Jupiter masses, and it may or may not be occurring in planet c.

References