HD 217107 b
Encyclopedia
HD 217107 b is an extrasolar planet
approximately 64 light-year
s away from Earth in the constellation
of Pisces
(the Fish
). The planet was discovered orbiting the star HD 217107
approximately every seven day
s, classifying the planet as a hot Jupiter
. Because of the planet's somewhat eccentric
orbit, scientists were able to confirm another planet within the system (HD 217107 c
).
of the star it orbits, caused by the tug of its gravity. A study of the radial velocity of HD 217107 carried out in 1998 revealed that its motion along the line of sight varied over a 7.1 day cycle. The period and amplitude of this variation indicated that it was caused by a planet
ary companion in orbit around the star, with a minimum mass slightly greater than that of Jupiter
. The planet's mean distance from the star is less than one fifth of Mercury's
distance from the Sun
.
s (AU). Confirmation of the existence of a second planet, HD 217107 c
, followed in 2005.
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 64 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 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 Fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
). The planet was discovered orbiting the star HD 217107
HD 217107
HD 217107 is a yellow subgiant star approximately 65 light-years away from Earth in the constellation of Pisces . Its mass is very similar to the Sun's, although it is considerably older...
approximately every seven 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, classifying the planet as a hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
. Because of the planet's somewhat eccentric
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...
orbit, scientists were able to confirm another planet within the system (HD 217107 c
HD 217107 c
HD 217107 c is an extrasolar planet approximately 64 light-years away from Earth in the constellation of Pisces . The planet was the second planet to be discovered orbiting the star HD 217107...
).
Discovery
As with the majority of extrasolar planet discoveries so far, it was found by detecting small variations in the 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...
of the star it orbits, caused by the tug of its gravity. A study of the radial velocity of HD 217107 carried out in 1998 revealed that its motion along the line of sight varied over a 7.1 day cycle. The period and amplitude of this variation indicated that it was caused by a planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
ary companion in orbit around the star, with a minimum mass slightly greater than 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,...
. The planet's mean distance from the star is less than one fifth of Mercury's
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...
distance from 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...
.
Indication of second planet
While most planets with orbital periods of less than 10 days have almost circular orbits, HD 217107 b has a somewhat eccentric orbit, and its discoverers hypothesized that this could be due to the gravitational influence of a second planet in the system at a distance of several astronomical unitAstronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s (AU). Confirmation of the existence of a second planet, HD 217107 c
HD 217107 c
HD 217107 c is an extrasolar planet approximately 64 light-years away from Earth in the constellation of Pisces . The planet was the second planet to be discovered orbiting the star HD 217107...
, followed in 2005.