HD 40307 c
Encyclopedia
HD 40307 c is an extrasolar planet
orbiting the star
HD 40307, located 42 light-year
s 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. Of the three known planets in the HD 40307 star system, it is the second largest of three "Super-Earth
" planets, and has the second furthest orbit from the star. 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.
and HD 40307 d
, orbiting the star HD 40307, HD 40307 c was discovered by measuring variations in the radial velocity
of HD 40307 caused by the star's orbit around the center of mass of the planetary system. These measurements were made by the High Accuracy Radial Velocity Planet Searcher
spectrograph apparatus (HARPS) at the La Silla Observatory
in Chile
's Atacama Desert
. The discovery of planets in the HD 40307 system was announced in an astrophysics convention that took place in Nantes
, France
in mid-June 2008.
and the larger HD 40307 d
. The planet orbits HD 40307 at 0.081 astronomical unit
s (AU), as compared to the Earth
's distance from the Sun
at 1 AU; as a result, one year on the planet constitutes approximately 9.6 Earth days. Analysis of the radial velocity data used to detect the planet does not yield a statistically-significant deviation from a circular orbit.
The star around which the planet HD 40307 orbits has a low metallicity, unusual when compared to 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 c 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 HD 40307 c was detected through the radial velocity method, rather than observed directly or via a transit, more specific characteristics (such as surface temperature
, composition and radius
) cannot be determined.
Since strong tidal forces
are predicted to result in the destruction of larger natural satellite
s of planets located close to their parent star, it is unlikely that HD 40307 c 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 away 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. Of the three known planets in the HD 40307 star system, it is the second largest of three "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, and has the second furthest orbit from the star. 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
Like the other two exoplanets, 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...
and HD 40307 d
HD 40307 d
HD 40307 d is an extrasolar planet orbiting the star HD 40307, located 42 light-years 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...
, orbiting the star HD 40307, HD 40307 c was discovered by measuring variations in 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...
of HD 40307 caused by the star's orbit around the center of mass of the planetary system. These measurements were made 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...
spectrograph apparatus (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 discovery of planets in the HD 40307 system was announced in an astrophysics convention that took place 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...
in mid-June 2008.
Orbit and mass
HD 40307 c is the second most massive planet in the system, with a lower mass bound, 6.8 times the mass of the Earth, which is between those of the smaller 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...
and the larger HD 40307 d
HD 40307 d
HD 40307 d is an extrasolar planet orbiting the star HD 40307, located 42 light-years 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...
. The planet orbits HD 40307 at 0.081 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s (AU), as compared to the 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 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...
at 1 AU; as a result, one year on the planet constitutes approximately 9.6 Earth days. Analysis of the radial velocity data used to detect the planet does not yield a statistically-significant deviation from a circular orbit.
The star around which the planet HD 40307 orbits has a low metallicity, unusual when compared to 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 c's small mass of at least 6.9 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 c 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 (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
, 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 HD 40307 c was detected through the radial velocity method, rather than observed directly or via a transit, more specific characteristics (such as 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...
, composition and 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...
) cannot be determined.
Since 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....
are predicted to 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 of planets located close to their parent star, it is unlikely that HD 40307 c hosts any satellites.