HD 40307 is an orange ( K-type)

main-sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of star ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

located approximately 42

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Pictor (the

Easel An easel is an upright support used for displaying and/or fixing something resting upon it, at an angle of about 20° to the vertical. In particular, painters traditionally use an easel to support a painting while they work on it, normally stan ...

), taking its primary name from its

Henry Draper Catalogue The ''Henry Draper Catalogue'' (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the ''Henry Draper Extension'' (HDE), published between 192 ...

designation. It is calculated to be slightly less massive than the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. The star has six known

planets A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the te ...

, three discovered in 2008 and three more in 2012. One of them, HD 40307 g, is a potential

super-Earth A super-Earth is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to t ...

in the

habitable zone In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressu ...

, with an orbital period of about 200 days. This object might be capable of supporting liquid water on its surface, although much more information must be acquired before its habitability can be assessed. No stellar companions to HD 40307 were detected as of 2018.

History and nomenclature

HD 40307 was observed during or before 1900 as part of the Cape Photographic Durchmusterung. The designation ''HD 40307'' is from the

, which is based on spectral classifications made between 1911 and 1915 by

Annie Jump Cannon Annie Jump Cannon (; December 11, 1863 – April 13, 1941) was an American astronomer whose cataloging work was instrumental in the development of contemporary stellar classification. With Edward C. Pickering, she is credited with the creation of ...

and her co-workers, and was published between 1918 and 1924.

Characteristics

As a K-type star, HD 40307 emits orange-tinted light. It has only about three-quarters of the

's radius and mass. Its temperature is measured at slightly under . The astronomers who discovered the planets orbiting HD 40307 suggested that the metallicities of stars determine whether or not the planetary bodies that orbit them will be terrestrial, like Earth, or gaseous, like

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

and

Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

Distance and visibility

Despite its relative proximity to the Sun at 42 light-years, HD 40307 is not visible to the naked eye, given its

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 7.17. It came within 6.4 light-years of the Sun about 413,000 years ago.

Planetary system

A planetary system around HD 40307 contains four confirmed planets and two other possible planets, all within of the star. After spending five years observing the star, the European Organisation for Astronomical Research in the Southern Hemisphere (''ESO'') announced that they had discovered three

s in orbit around HD 40307 in June 2008. All three planets were detected by the

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

method, using the

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision Echelle grating, echelle planet-finding spectrograph installed in 2002 on the ESO 3.6 m Telescope, ESO's 3.6m telescope at La Silla Observatory in Chile. The First l ...

spectrograph system. In 2012, an independent analysis carried out by a team of astronomers led by Mikko Tuomi of the University of Hertfordshire confirmed the existence of these planets and found an additional three planets in the systems. The planet HD 40307 f on 51.6-day orbit was confirmed in 2015, with inconclusive evidence for the planets HD 40307 e and HD 40307 g. Five of the planets orbit very close to the star, with the farthest of them located twice as close to HD 40307 than is the planet Mercury is to the

.Mercury orbits at approx. 0.39 AU The outermost planet orbits at a distance similar to the distance of

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

to the

and is situated well in the system's

liquid water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known living organisms ( ...

. The

minimum mass In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars, binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets detected by the radial velocit ...

es of the planets in the system ranges from three to ten times the mass of the Earth, placing them somewhere between

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

and gas giants like

Uranus Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a Supercritical fluid, supercritical phase of matter, which astronomy calls "ice" or Volatile ( ...

and

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

. Dynamical analysis of the innermost planets suggests that planet b is unstable at its age unless it is an ice giant, having migrated from further away. That implies similar for the other planets, even further out. The most recent discovery also indicates via dynamical analysis that the true planetary masses can not be much higher than their minimum masses.

Notes

References

External links

A Trio of Super-Earths: A harvest of low-mass exoplanets discovered with HARPS
press release,

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 m ...

, ESO 19/08, June 16, 2008. {{DEFAULTSORT:HD 40307 040307 027887

2046 In contemporary history, the third millennium is the current millennium in the ''Anno Domini'' or Common Era, under the Gregorian calendar. It began on 1 January 2001 ( MMI) and will end on 31 December 3000 ( MMM), spanning the 21st to 30 ...

CD-60 01303 K-type main-sequence stars HD, 040307 Pictor Planetary systems with four confirmed planets J05540421-6001245