HD 74156
Encyclopedia
HD 74156 is a yellow dwarf
star
(spectral type
G0V) in the constellation
of Hydra
, 211 light years
from our solar system
. It is known to be orbited by two giant planet
s.
. The total luminosity is 2.96 times that of our Sun and its temperature 5960 K. The age of the star is estimated at approximately 3.7 billion years, with metallicity 1.35 times that of the Sun based on its abundance of iron
.
orbits the star at a distance closer than Mercury
is to our Sun, in an extremely eccentric orbit. The second planet HD 74156 c
is a long-period, massive planet (at least 8 times the mass of Jupiter), which orbits the star in an elliptical orbit with a semimajor axis of 3.90 astronomical unit
s.
es, an additional Saturn-mass planet would be stable in a region between 0.9 and 1.4 AU between the orbits of the two known planets. Under the "packed planetary systems" hypothesis, which predicts that planetary systems form in such a way that the system could not support additional planets between the orbits of the existing ones, the gap would be expected to host a planet.
In September 2007, a third planet with a mass at least 0.396 Jupiter masses was announced to be orbiting between planets b and c with an eccentric orbit
. The planet, orbiting in a region of the planetary system previously known to be stable for additional planets, was seen as a confirmation of the "packed planetary systems" hypothesis. However, Roman V. Baluev has cast doubt on this discovery, suggesting that the observed variations may be due to annual errors in the data. A subsequent search using the Hobby-Eberly Telescope
also failed to confirm the planet, and further data obtained using HIRES instrument strongly contradicts its existence.
Yellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
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...
(spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
G0V) 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 Hydra
Hydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...
, 211 light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
from 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...
. It is known to be orbited by two giant 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,...
s.
Star
This star is 24% more massive and 64% larger than our SunSun
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...
. The total luminosity is 2.96 times that of our Sun and its temperature 5960 K. The age of the star is estimated at approximately 3.7 billion years, with metallicity 1.35 times that of the Sun based on its abundance of 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...
.
Planetary system
In April 2001, two giant planets were announced orbiting the star. The first planet HD 74156 bHD 74156 b
HD 74156 b is an extrasolar planet at least 1.88 times the mass of Jupiter that orbits the star HD 74156. It is most likely a gas giant. This planet was discovered in April 2001 by Dominique Naef and Michel Mayor along with the second planet HD 74156 c....
orbits the star at a distance 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...
is to our Sun, in an extremely eccentric orbit. The second planet HD 74156 c
HD 74156 c
HD 74156 c is an extrasolar planet at least eight times the mass of Jupiter orbiting the star HD 74156. It is most likely a gas giant. This planet was discovered by Dominique Naef and Michel Mayor in April 2001 together with the first planet HD 74156 b....
is a long-period, massive planet (at least 8 times the mass of Jupiter), which orbits the star in an elliptical orbit with a semimajor axis of 3.90 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s.
Claims of a third planet
Given the two-planet configuration of the system under the assumption that the orbits are coplanar and have masses equal to their minimum massMinimum 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...
es, an additional Saturn-mass planet would be stable in a region between 0.9 and 1.4 AU between the orbits of the two known planets. Under the "packed planetary systems" hypothesis, which predicts that planetary systems form in such a way that the system could not support additional planets between the orbits of the existing ones, the gap would be expected to host a planet.
In September 2007, a third planet with a mass at least 0.396 Jupiter masses was announced to be orbiting between planets b and c with an eccentric orbit
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...
. The planet, orbiting in a region of the planetary system previously known to be stable for additional planets, was seen as a confirmation of the "packed planetary systems" hypothesis. However, Roman V. Baluev has cast doubt on this discovery, suggesting that the observed variations may be due to annual errors in the data. A subsequent search using the Hobby-Eberly Telescope
Hobby-Eberly Telescope
The Hobby-Eberly Telescope is a 9.2-meter aperture telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs...
also failed to confirm the planet, and further data obtained using HIRES instrument strongly contradicts its existence.