HD 40307 b
Encyclopedia
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 somewhat larger than the Earth, discovered orbiting the star. The planet is of interest as this star has relatively low metallicity
, supporting a hypothesis that different metallicities in protostars
determine what kind of planets they will form.
of the star it orbits. These measurements were made by the High Accuracy Radial Velocity Planet Searcher
(HARPS) spectrograph at the Chile
-based La Silla Observatory
. The discovery was announced at the astrophysics conference that took place in Nantes, France
between 16 and 18 June 2008. HD 40307 b was one of three "Super-Earth" exoplanets found orbiting the star HD 40307.
The star around which HD 40307 b orbits has a low metallicity, 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.
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, as the planet was discovered via radial velocity measurements rather than by transit or by imaging, more specific characteristics, such as its radius
, composition, and possible surface temperature
cannot be determined.
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 b 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 HD 40307, located 42 light-years away in the direction of the southern constellation 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
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, 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 smallest of three "Super-Earths", planets somewhat larger than the Earth, discovered orbiting 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 protostars
Protostars
Protostars is an anthology of science fiction short stories edited by David Gerrold and Stephen Goldin. It was first published in paperback by Ballantine Books in October 1971, and has been reprinted a number of times since....
determine what kind of planets they will form.
Discovery
As with many other extrasolar planets, HD 40307 b was discovered by measuring 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. 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...
(HARPS) spectrograph at the 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...
-based 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...
. The discovery was announced at the astrophysics conference that took place in Nantes, 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...
between 16 and 18 June 2008. HD 40307 b was one of three "Super-Earth" exoplanets found orbiting the star HD 40307.
Orbit and Mass
While HD 40307 b is considered a "Super-Earth" planet, it is the lightest planet discovered in the system, with at least 4.2 times the mass of the Earth. The planet orbits the star HD 40307 every 4.3 Earth days, corresponding of its location at approximately 0.047 astronomical units from the star. 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 b orbits has a low metallicity, 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
With a lower mass bound of 4.2 times the mass of the Earth, HD 40307 b is presumably too small to be a jovian planet. This concept was challenged in a 2009 study, which stated that if HD 40307 b is terrestrial, the planet would be highly unstable and would be affected by tidal heatingTidal 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, as the planet was discovered via radial velocity measurements rather than by transit or by imaging, more specific characteristics, such as its 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 possible 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 determined.
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 b hosts any satellites.