Upsilon Andromedae c
Encyclopedia
Upsilon Andromedae c is an extrasolar planet
or star orbit
ing the Sun
-like star
Upsilon Andromedae A
every 241.2 days. Its discovery in April 1999 by Geoffrey Marcy
and R. Paul Butler
made Upsilon Andromedae the first known star (excluding the pulsar
PSR 1257+12) to host a multiple-planet planetary system
. Upsilon Andromedae c is the second known planet (if a planet) in order of distance from its star.
as a result of the planet's gravity. This was done by making precise measurements of the Doppler shift of the spectrum
of Upsilon Andromedae A. At the time of discovery, Upsilon Andromedae A was already known to host one extrasolar planet, the hot Jupiter
Upsilon Andromedae b
, 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
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
.
extrasolar planets, the orbit of Upsilon Andromedae c is eccentric, more so than any of the major planets in our solar system
(including Pluto
). If placed in our solar system, Upsilon Andromedae c would lie between the orbits of Earth and Venus
.
The high orbital eccentricity may be the result of gravitational 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 6,700 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; it is unclear how likely this situation might be. Other models are possible.
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
can be obtained. However, by combining radial velocity measurements from ground-based telescopes with astrometric data from the Hubble Space Telescope
, astronomers have determined the orbital inclination as well as the actual mass
of Upsilon Andromedae c, which is about 13.98 times the mass of Jupiter
. The mutual inclination
between c and d is 29.9 degrees. That, however, means that Upsilon Andromedae c narrowly exceeds 13 times the mass of Jupiter, which is the dividing line between planets and (brown dwarf) stars.
or brown dwarf with no solid surface. Since the planet has only been detected indirectly through observations of its star, properties such as its radius
, composition, and temperature
are unknown.
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
or star orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
ing the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
-like star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
Upsilon Andromedae A
Upsilon Andromedae
Upsilon Andromedae is a binary star located approximately 44 light-years away from Earth in the constellation Andromeda. The primary star is a yellow-white dwarf star that is somewhat younger than the Sun...
every 241.2 days. Its discovery in April 1999 by Geoffrey Marcy
Geoffrey Marcy
Geoffrey W. Marcy is an American astronomer, who is currently Professor of Astronomy at the University of California, Berkeley, famous for discovering more extrasolar planets than anyone else, 70 out of the first 100 to be discovered, along with R...
and R. Paul Butler
R. Paul Butler
R. Paul Butler is an astronomer who searches for extrasolar planets.He received a BA and an MS from San Francisco State University, completing a Master's thesis with Geoffrey Marcy, and then completed his doctoral studies at the University of Maryland, College Park in 1993...
made Upsilon Andromedae the first known star (excluding the pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
PSR 1257+12) to host a multiple-planet planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
. Upsilon Andromedae c is the second known planet (if a planet) in order of distance from its star.
Discovery
Like the majority of known extrasolar planets, Upsilon Andromedae c was detected by measuring variations in its star's radial velocityRadial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
as a result of the planet's gravity. This was done by making precise measurements of the Doppler shift of the spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
of Upsilon Andromedae A. At the time of discovery, Upsilon Andromedae A was already known to host one extrasolar planet, the hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
Upsilon Andromedae b
Upsilon Andromedae b
Upsilon Andromedae b, occasionally referred to as Upsilon Andromedae Ab , is an extrasolar planet approximately 44 light-years away from Earth in the constellation of Andromeda . The planet was discovered orbiting the Solar twin star, Upsilon Andromedae, approximately every five days...
, 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 University is a public university located in San Francisco, California. As part of the 23-campus California State University system, the university offers over 100 areas of study from nine academic colleges...
and the Harvard-Smithsonian Center for Astrophysics
Harvard-Smithsonian Center for Astrophysics
The Harvard–Smithsonian Center for Astrophysics is one of the largest and most diverse astrophysical institutions in the world, where scientists carry out a broad program of research in astronomy, astrophysics, earth and space sciences, and science education...
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
Upsilon Andromedae d is an extrasolar planet orbiting the Sun-like star Upsilon Andromedae A. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first star to be known to host a multiple-planet planetary system...
.
Orbit and mass
Like the majority of long-periodOrbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
extrasolar planets, the orbit of Upsilon Andromedae c is eccentric, more so than any of the major planets in our solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
(including Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
). If placed in our solar system, Upsilon Andromedae c would lie between the orbits of Earth and Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
.
The high orbital eccentricity may be the result of gravitational 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 6,700 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; it is unclear how likely this situation might be. Other models are possible.
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
Minimum mass
In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets...
can be obtained. However, by combining radial velocity measurements from ground-based telescopes with astrometric data from the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
, astronomers have determined the orbital inclination as well as the actual mass
True mass
The term true mass is synonymous with the term mass, but is used in astronomy to differentiate the measured mass of a planet from the lower limit of mass usually obtained from radial velocity techniques...
of Upsilon Andromedae c, which is about 13.98 times the mass of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. The mutual inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
between c and d is 29.9 degrees. That, however, means that Upsilon Andromedae c narrowly exceeds 13 times the mass of Jupiter, which is the dividing line between planets and (brown dwarf) stars.
Characteristics
Given the planet's high mass, it is likely that Upsilon Andromedae c is a gas giantGas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
or brown dwarf with no solid surface. Since the planet has only been detected indirectly through observations of its star, properties such as its radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
, composition, and temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
are unknown.
See also
- Eccentric JupiterEccentric JupiterAn eccentric Jupiter is a Jovian planet that orbits its star in an eccentric orbit. Eccentric Jupiters may disqualify a planetary system from having Earth-like planets in it because a massive gas giant with an eccentric orbit may remove all Earth mass planets from the habitable zone.To date, it...