HD 40307 d
Encyclopedia
HD 40307 d is an extrasolar planet
orbiting the star
HD 40307, located 42 light-year
s from Earth in the direction of the southern constellation
Pictor
. The planet was discovered by the radial velocity method, using the HARPS
apparatus in June 2008. It is the most massive of the three known "Super-Earth
" planets in the system, and is the most distant known satellite of HD 40307. The planet is of interest as this star has relatively low metallicity
, supporting a hypothesis that different metallicities in protostar
s determine what kind of planets they will form.
method, which functions by measuring the variations in radial velocity
in a star produced by the gravitational effect of orbiting exoplanets. The radial velocities were measured by the High Accuracy Radial Velocity Planet Searcher
spectrography system (HARPS) at the La Silla Observatory
in Chile
's Atacama Desert
. The two other less massive planets, HD 40307 b
and HD 40307 c
, orbiting HD 40307 were discovered in the same way. The discovery of HD 40307 d and other planets in the system was announced at the astrophysics conference that took place on June 16–18, 2008 in Nantes
, France
.
, a planet with at least 4.2 times the mass of Earth. The planet orbits approximately 0.134 astronomical units from its primary star, as compared to Earth
's orbit at approximately one astronomical unit away from the Sun
. As a result, one year on HD 40307 d constitutes approximately 20.46 Earth days, the longest period of all the planets in the system. The eccentricity of the planet's orbit was found to not differ significantly from zero, meaning that there is insufficient data to distinguish the orbit from an entirely circular one.
The star around which HD 40307 d orbits has an unusually low metallicity compared to that of other planet-bearing stars. This supports a hypothesis concerning the possibility that the metallicity of stars during their births may determine whether a protostar
's accretion disk forms gas giants or terrestrial planets.
. This concept was challenged in a 2009 study, which stated that if HD 40307 d is terrestrial, the planet would be highly unstable and would be affected by tidal heating
in a manner greater than Io
, a volcanic satellite of planet Jupiter
; restrictions that seem to bind terrestrial planets, however, do not restrict Jovian planets like Neptune
or Uranus
. However, because the planet was discovered through radial velocity, rather than by transit or direct imaging, more specific physical characteristics such as radius
, composition, and average surface temperature
cannot be observed.
As strong tidal forces
often result in the destruction of larger natural satellite
s in planets orbiting close to a star, it is unlikely that HD 40307 d hosts any satellites.
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...
orbiting the 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...
HD 40307, located 42 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 direction of the southern 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....
Pictor
Pictor
Pictor is a small and faint constellation in the southern sky , located between the brilliant star Canopus and the Large Magellanic Cloud. Its name is Latin for painter, but it is in fact an abbreviation of its original name Equuleus Pictoris, the 'painter's easel', and it is normally represented...
. The planet was discovered by the radial velocity method, using the HARPS
High Accuracy Radial Velocity Planet Searcher
The High Accuracy Radial velocity Planet Searcher is a high-precision echelle spectrograph installed in 2002 on ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003...
apparatus in June 2008. It is the most massive of the three known "Super-Earth
Super-Earth
A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below the mass of the Solar System's gas giants. The term super-Earth refers only to the mass of the planet, and does not imply anything about the surface conditions or habitability...
" planets in the system, and is the most distant known satellite of HD 40307. The planet is of interest as this star has relatively low metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
, supporting a hypothesis that different metallicities in protostar
Protostar
A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...
s determine what kind of planets they will form.
Discovery
HD 40307 d was discovered through the Doppler spectroscopyDoppler spectroscopy
Doppler spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler shifts in the spectrum of the star around which the planet orbits....
method, which functions by measuring the variations in 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...
in a star produced by the gravitational effect of orbiting exoplanets. The radial velocities were measured by the High Accuracy Radial Velocity Planet Searcher
High Accuracy Radial Velocity Planet Searcher
The High Accuracy Radial velocity Planet Searcher is a high-precision echelle spectrograph installed in 2002 on ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003...
spectrography system (HARPS) at the La Silla Observatory
La Silla Observatory
La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory organisation, and several others are partly maintained by ESO...
in Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
's Atacama Desert
Atacama Desert
The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...
. The two other less massive planets, HD 40307 b
HD 40307 b
HD 40307 b is an extrasolar planet orbiting the star HD 40307, located 42 light-years away in the direction of the southern constellation Pictor. The planet was discovered by the radial velocity method, using the HARPS apparatus, in June 2008; it is the smallest of three "Super-Earths", planets...
and HD 40307 c
HD 40307 c
HD 40307 c is an extrasolar planet orbiting the star HD 40307, located 42 light-years away in the direction of the southern constellation Pictor. The planet was discovered by the radial velocity method, using the HARPS apparatus, in June 2008...
, orbiting HD 40307 were discovered in the same way. The discovery of HD 40307 d and other planets in the system was announced at the astrophysics conference that took place on June 16–18, 2008 in Nantes
Nantes
Nantes is a city in western France, located on the Loire River, from the Atlantic coast. The city is the 6th largest in France, while its metropolitan area ranks 8th with over 800,000 inhabitants....
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
.
Orbit and mass
HD 40307 d has a mass of at least 9.2 times Earth's; assuming that all planets in the system have coplanar orbits, it is the most massive planet known in the system and around twice as massive as HD 40307 bHD 40307 b
HD 40307 b is an extrasolar planet orbiting the star HD 40307, located 42 light-years away in the direction of the southern constellation Pictor. The planet was discovered by the radial velocity method, using the HARPS apparatus, in June 2008; it is the smallest of three "Super-Earths", planets...
, a planet with at least 4.2 times the mass of Earth. The planet orbits approximately 0.134 astronomical units from its primary star, as compared to Earth
Earth
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...
's orbit at approximately one astronomical unit away 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...
. As a result, one year on HD 40307 d constitutes approximately 20.46 Earth days, the longest period of all the planets in the system. The eccentricity of the planet's orbit was found to not differ significantly from zero, meaning that there is insufficient data to distinguish the orbit from an entirely circular one.
The star around which HD 40307 d orbits has an unusually low metallicity compared to that of other planet-bearing stars. This supports a hypothesis concerning the possibility that the metallicity of stars during their births may determine whether a protostar
Protostar
A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...
's accretion disk forms gas giants or terrestrial planets.
Characteristics
Despite HD 40307 d's small mass of at least 9.2 times Earth's, it is assumed that the planet is too small to be 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...
. This concept was challenged in a 2009 study, which stated that if HD 40307 d is terrestrial, the planet would be highly unstable and would be affected by tidal heating
Tidal heating
Tidal heating occurs through the tidal friction processes: orbital and rotational energy are dissipated as heat in the crust of the moons and planets involved. Io, a moon of Jupiter, is the most volcanically active body in the solar system, with no impact craters surviving on its surface...
in a manner greater than Io
IO
Io, IO, I/O, i/o, or i.o. may refer to:-An abbreviation:* I.O., a theater in Chicago, Illinois dedicated to improvisational comedy* i.o., "in illo ordine", Latin phrase meaning "respectively"...
, a volcanic satellite of planet 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,...
; restrictions that seem to bind terrestrial planets, however, do not restrict Jovian planets like Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
or Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
. However, because the planet was discovered through radial velocity, rather than by transit or direct imaging, more specific physical characteristics such as 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 average surface 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...
cannot be observed.
As strong 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....
often result in the destruction of larger natural satellite
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....
s in planets orbiting close to a star, it is unlikely that HD 40307 d hosts any satellites.