Upsilon Andromedae b
Encyclopedia
Upsilon Andromedae b, occasionally referred to as Upsilon Andromedae Ab (to distinguish it from the red dwarf
star
Upsilon Andromedae B
), is an extrasolar planet
approximately 44 light-year
s away from Earth in the constellation
of Andromeda
(the Chained Maiden
). The planet was discovered orbiting the Solar twin star, Upsilon Andromedae
, approximately every five days. Discovered in June 1996 by Geoffrey Marcy
and R. Paul Butler
, it was one of the first hot Jupiter
s to be discovered. Upsilon Andromedae b is the innermost known planet in its planetary system
.
caused by the planet's gravity. The variations were detected by making sensitive measurements of the Doppler shift of Upsilon Andromedae's spectrum
. The planet was announced in January 1997, together with 55 Cancri b
and the planet orbiting Tau Boötis
.
Like 51 Pegasi b
, the first extrasolar planet discovered around a normal star, Upsilon Andromedae b orbits very close to its star, closer than Mercury
does to our Sun. The planet takes 4.617 day
s to complete an orbit, with a semimajor axis of 0.0595 AU
.
A limitation of the radial velocity method used to detect Upsilon Andromedae b is that only a lower limit on the mass
can be found. In the case of Upsilon Andromedae b, this lower limit is 68.7% of the mass of Jupiter
, though depending on the inclination
of the orbit, the true mass
may be much greater. However, astronomers found recently that inclination of the orbital plane
is around 25° and the true mass
may be about 1.4 MJ
. Coplanarity is not to be assumed; the mutual inclination between c and d is 35 degrees.
with no solid
surface. Since the planet has only been detected indirectly, properties such as its radius
and composition are unknown.
The Spitzer Space Telescope
measured the planet temperature
, and found that the difference between the two sides of Upsilon Andromedae b of about 1,400 degrees Celsius, ranging from minus 20 to 230 degrees to about 1,400 to 1,650 degrees Celsius. The temperature difference has led to speculation that Upsilon Andromedae b is tidal locked
with the same side always facing Upsilon Andromedae A.
Sudarsky had, on the assumption that the planet is similar to Jupiter in composition and that its environment is close to chemical equilibrium
, predicted Upsilon Andromedae b to have reflective cloud
s of silicates
and iron
in its upper atmosphere
. The cloud deck instead absorbs the sun's radiation; between that and the hot, high pressure gas surrounding the mantle, exists a stratosphere
of cooler gas. The outer shell of dark, opaque, hot cloud is assumed to consist of vanadium and titanium oxides ("pM planets"), but other compounds like tholins cannot be ruled out as of yet.
The planet is unlikely to have large moons
, since tidal forces
would either eject them from orbit or destroy them on short timescales compared to the age of the system.
The planet (with 51 Pegasi b
) is deemed a candidate for direct imaging by Planetpol
.
activity on its parent star. Observations suggest that there is a "hot spot" on the star around 169° away from the sub-planetary point. This may be the result of interactions between the magnetic field
s of the planet and the star. The mechanism may be similar to that responsible for the activity of RS Canum Venaticorum variable
stars, or the interaction between Jupiter and its moon Io
.
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
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 B
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...
), is an extrasolar planet
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...
approximately 44 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away from Earth in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Andromeda
Andromeda (constellation)
Andromeda is a constellation in the northern sky. It is named after Andromeda, the princess in the Greek legend of Perseus who was chained to a rock to be eaten by the sea monster Cetus...
(the Chained Maiden
Virginity
Virginity refers to the state of a person who has never engaged in sexual intercourse. There are cultural and religious traditions which place special value and significance on this state, especially in the case of unmarried females, associated with notions of personal purity, honor and worth...
). The planet was discovered orbiting the Solar twin star, Upsilon Andromedae
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...
, approximately every five days. Discovered in June 1996 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...
, it was one of the first hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
s to be discovered. Upsilon Andromedae b is the innermost known planet in its 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...
.
Discovery
Like the majority of known extrasolar planets, Upsilon Andromedae b was detected by the 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...
caused by the planet's gravity. The variations were detected by making sensitive measurements of the Doppler shift of Upsilon Andromedae's 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...
. The planet was announced in January 1997, together with 55 Cancri b
55 Cancri b
55 Cancri b is an extrasolar planet orbiting the Sun-like star 55 Cancri A every 14.65 days. It is the second planet in order of distance from its star, and is an example of a hot Jupiter. Discovered in 1996 by Geoffrey Marcy and R...
and the planet orbiting Tau Boötis
Tau Boötis
Tau Boötis is a yellow-white dwarf approximately 51 light-years away in the constellation of Boötes. The system is also a binary star system, with the secondary star being a red dwarf...
.
Like 51 Pegasi b
51 Pegasi b
51 Pegasi b , sometimes though unofficially named Bellerophon, is an extrasolar planet approximately 50 light-years away in the constellation of Pegasus...
, the first extrasolar planet discovered around a normal star, Upsilon Andromedae b orbits very close to its star, closer than Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
does to our Sun. The planet takes 4.617 day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
s to complete an orbit, with a semimajor axis of 0.0595 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
.
A limitation of the radial velocity method used to detect Upsilon Andromedae b is that only a lower limit on the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
can be found. In the case of Upsilon Andromedae b, this lower limit is 68.7% of 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,...
, though depending on the 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...
of the orbit, the true 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...
may be much greater. However, astronomers found recently that inclination of the orbital plane
Orbital plane (astronomy)
All of the planets, comets, and asteroids in the solar system are in orbit around the Sun. All of those orbits line up with each other making a semi-flat disk called the orbital plane. The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded...
is around 25° and the true 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...
may be about 1.4 MJ
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
. Coplanarity is not to be assumed; the mutual inclination between c and d is 35 degrees.
Physical characteristics
Given the planet's high mass, it is likely that Upsilon Andromedae b 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...
with no solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
surface. Since the planet has only been detected indirectly, 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...
and composition are unknown.
The Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
measured the planet 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...
, and found that the difference between the two sides of Upsilon Andromedae b of about 1,400 degrees Celsius, ranging from minus 20 to 230 degrees to about 1,400 to 1,650 degrees Celsius. The temperature difference has led to speculation that Upsilon Andromedae b is tidal locked
Tidal locking
Tidal locking occurs when the gravitational gradient makes one side of an astronomical body always face another; for example, the same side of the Earth's Moon always faces the Earth. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner...
with the same side always facing Upsilon Andromedae A.
Sudarsky had, on the assumption that the planet is similar to Jupiter in composition and that its environment is close to chemical equilibrium
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
, predicted Upsilon Andromedae b to have reflective cloud
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
s of silicates
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
in its upper atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
. The cloud deck instead absorbs the sun's radiation; between that and the hot, high pressure gas surrounding the mantle, exists a stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
of cooler gas. The outer shell of dark, opaque, hot cloud is assumed to consist of vanadium and titanium oxides ("pM planets"), but other compounds like tholins cannot be ruled out as of yet.
The planet is unlikely to have large moons
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
, since tidal forces
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
would either eject them from orbit or destroy them on short timescales compared to the age of the system.
The planet (with 51 Pegasi b
51 Pegasi b
51 Pegasi b , sometimes though unofficially named Bellerophon, is an extrasolar planet approximately 50 light-years away in the constellation of Pegasus...
) is deemed a candidate for direct imaging by Planetpol
PlanetPol
PlanetPol is a ground based extrasolar planet search device. Based at William Herschel Telescope....
.
Effect on its sun
Upsilon Andromedae b appears to be responsible for increased chromosphericChromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....
activity on its parent star. Observations suggest that there is a "hot spot" on the star around 169° away from the sub-planetary point. This may be the result of interactions between the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s of the planet and the star. The mechanism may be similar to that responsible for the activity of RS Canum Venaticorum variable
RS Canum Venaticorum variable
RS Canum Venaticorum variables are a type of variable star. They are close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity...
stars, or the interaction between Jupiter and its moon Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
.