47 Ursae Majoris b
Encyclopedia
47 Ursae Majoris b (sometimes abbreviated 47 Uma b) is an extrasolar planet
approximately 46 light-year
s from Earth in the constellation
of Ursa Major
. The planet was discovered located in a long-period
orbit around the star 47 Ursae Majoris
in January 1996 and as of 2011 is the innermost of three known planets in its planetary system
. It has a mass
at least 2.53 times that of Jupiter
.
as the planet's gravity pulls the star around. This was achieved by observing the Doppler shift of the spectrum
of 47 Ursae Majoris. After the discovery of the first extrasolar planet around a Sun-like star, 51 Pegasi b
, astronomers Geoffrey Marcy
and R. Paul Butler
searched through their observational data for signs of extrasolar planets and soon discovered two: 47 Ursae Majoris b and 70 Virginis b
. The discovery of 47 Ursae Majoris b was announced in 1996.
47 Ursae Majoris b orbits at a distance of 2.10 AU
from its star, taking 1,078 days or 2.95 years to complete a revolution. It was the first long-period planet around a main sequence
star to be discovered. Unlike the majority of known long-period extrasolar planets, the eccentricity of the orbit of 47 Ursae Majoris b is low.
A limitation of the radial velocity method used to detect 47 Ursae Majoris b is that only a lower limit on the planet's mass can be obtained. Preliminary astrometric measurements made by the Hipparcos
satellite suggest the planet's orbit is inclined
at an angle of 63.1° to the plane of the sky, which would imply a true mass
12% greater than the lower limit determined by radial velocity measurements. However, subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterise the orbits of substellar companions, and the true inclination of the orbit (and hence the true mass) are regarded as unknown.
with no solid
surface. Since the planet has only been detected indirectly, properties such as its radius
, composition, and temperature
are unknown. Due to its mass it is likely to have a surface gravity 6–8 times that of Earth. Assuming a composition similar to that of Jupiter and an environment close to chemical equilibrium
, the upper atmosphere of the planet is expected to contain water clouds, as opposed to the ammonia
clouds typical of Jupiter.
While 47 Ursae Majoris b lies outside its star's habitable zone
, its gravitational influence would disrupt the orbit of planets in the outer part of the habitable zone. In addition, it may have disrupted the formation of terrestrial planet
s and reduced the delivery of water to any inner planets in the system. Therefore planets located in the habitable zone of 47 Ursae Majoris are likely to be small and dry.
It has been theorized that light reflections and infrared emissions from 47 UMa b, along with tidal influence, could warm any moons in orbit around it to be habitable, despite the planet being outside the normally accepted habitable zone.
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 46 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 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 Ursa Major
Ursa Major
Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
. The planet was discovered located in a long-period
Orbital 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...
orbit around the star 47 Ursae Majoris
47 Ursae Majoris
47 Ursae Majoris is a solar analog, yellow dwarf star approximately 46 light-years away from Earth in the constellation of Ursa Major. , it has been confirmed that three Jupiter-like extrasolar planets orbit the star...
in January 1996 and as of 2011 is the innermost of three known planets 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...
. It has a 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:...
at least 2.53 times that 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,...
.
Discovery
Like the majority of known extrasolar planets, 47 Ursae Majoris b was discovered by detecting the changes 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 the planet's gravity pulls the star around. This was achieved by observing 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 47 Ursae Majoris. After the discovery of the first extrasolar planet around a Sun-like star, 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...
, astronomers 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...
searched through their observational data for signs of extrasolar planets and soon discovered two: 47 Ursae Majoris b and 70 Virginis b
70 Virginis b
70 Virginis b is an extrasolar planet approximately 60 light-years away in the constellation of Virgo. Announced in 1996 by Geoffrey Marcy and R. Paul Butler, 70 Virginis was one of the first stars confirmed to have planets orbiting it...
. The discovery of 47 Ursae Majoris b was announced in 1996.
Orbit and mass
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
from its star, taking 1,078 days or 2.95 years to complete a revolution. It was the first long-period planet around a main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star to be discovered. Unlike the majority of known long-period extrasolar planets, the eccentricity of the orbit of 47 Ursae Majoris b is low.
A limitation of the radial velocity method used to detect 47 Ursae Majoris b is that only a lower limit on the planet's mass can be obtained. Preliminary astrometric measurements made by the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
satellite suggest the planet's orbit is inclined
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...
at an angle of 63.1° to the plane of the sky, which would imply a 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...
12% greater than the lower limit determined by radial velocity measurements. However, subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterise the orbits of substellar companions, and the true inclination of the orbit (and hence the true mass) are regarded as unknown.
Physical characteristics
Given the planet's high mass, it is likely that 47 Ursae Majoris 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...
, 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. Due to its mass it is likely to have a surface gravity 6–8 times that of Earth. Assuming a composition similar to that of Jupiter and an environment 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...
, the upper atmosphere of the planet is expected to contain water clouds, as opposed to the ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
clouds typical of Jupiter.
While 47 Ursae Majoris b lies outside its star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
, its gravitational influence would disrupt the orbit of planets in the outer part of the habitable zone. In addition, it may have disrupted the formation of terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
s and reduced the delivery of water to any inner planets in the system. Therefore planets located in the habitable zone of 47 Ursae Majoris are likely to be small and dry.
It has been theorized that light reflections and infrared emissions from 47 UMa b, along with tidal influence, could warm any moons in orbit around it to be habitable, despite the planet being outside the normally accepted habitable zone.
See also
- 47 Ursae Majoris in fiction