54 Piscium b
Encyclopedia
54 Piscium b occasionally catalogued as 54 Piscium Ab in order to differentiate from the brown dwarf
in the system, is an extrasolar planet
approximately 36 light-year
s away in the constellation
of Pisces
. The planet was discovered orbiting the orange dwarf star
54 Piscium
. The planet's minimum mass
is one fifth that of Jupiter
, and it orbits the star in a very eccentric orbit about every two month
s.
around 54 Piscium using the radial velocity
method, a process utilizes the "wobbling" effect that a star may experience if something is tugging on it, to define the presence of a planetary body. The planet has been estimated to have a mass
of only 20 percent that of Jupiter (making the planet around the same size and mass of Saturn
).
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The planet orbits its sun at a distance of 0.28 astronomical unit
s (which would be within the orbit of Mercury
), which takes approximately 62 day
s to complete. The planet has a high eccentricity
of about 0.63. The highly elliptical orbit, however, suggested that the gravity of an unseen object farther away from the star was pulling the planet outward. The eccentric orbit became clear with the discovery of the brown dwarf
within the system.
-like planet would need to be centered within 0.68 AU (around the orbital distance of Venus), which in a Keplerian system means a 240 day orbital period. In a 2006 simulation with the brown dwarf, 54 Piscium b's orbit "sweeps clean" most test particles within 0.5 AU, leaving only asteroids "in low-eccentricity orbits near the known planet’s apastron distance, near the 1:2 mean-motion resonance". Also, observation has ruled out Neptune-class or heavier planets with a period of one year or less; which still allows for Earth-sized planets at 0.6 AU or more.
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
in the system, 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 36 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 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 Pisces
Pisces (constellation)
Pisces is a constellation of the zodiac. Its name is the Latin plural for fish, and its symbol is . It lies between Aquarius to the west and Aries to the east...
. The planet was discovered orbiting the orange dwarf 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...
54 Piscium
54 Piscium
54 Piscium is an orange dwarf star approximately 36 light-years away in the constellation of Pisces. In 2002, an extrasolar planet was confirmed to be orbiting the star, and in 2006, a brown dwarf was also discovered orbiting it....
. The planet's minimum 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...
is one fifth 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,...
, and it orbits the star in a very eccentric orbit about every two month
Month
A month is a unit of time, used with calendars, which was first used and invented in Mesopotamia, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately...
s.
Discovery
On January 16, 2002, a team of astronomers (led by Geoff Marcy) announced the discovery of an extrasolar planetExtrasolar 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...
around 54 Piscium using the radial velocity
Radial 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...
method, a process utilizes the "wobbling" effect that a star may experience if something is tugging on it, to define the presence of a planetary body. The planet has been estimated to have 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:...
of only 20 percent that of Jupiter (making the planet around the same size and mass of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
).
Orbit and mass
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s (which would be within the orbit of 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...
), which takes approximately 62 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. The planet has a high eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of about 0.63. The highly elliptical orbit, however, suggested that the gravity of an unseen object farther away from the star was pulling the planet outward. The eccentric orbit became clear with the discovery of the brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
within the system.
Perturbation
The orbit of an EarthEarth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
-like planet would need to be centered within 0.68 AU (around the orbital distance of Venus), which in a Keplerian system means a 240 day orbital period. In a 2006 simulation with the brown dwarf, 54 Piscium b's orbit "sweeps clean" most test particles within 0.5 AU, leaving only asteroids "in low-eccentricity orbits near the known planet’s apastron distance, near the 1:2 mean-motion resonance". Also, observation has ruled out Neptune-class or heavier planets with a period of one year or less; which still allows for Earth-sized planets at 0.6 AU or more.