HD 82943 (164 G. Hydrae) is a yellow dwarf

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

approximately 89

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

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 origins of the e ...

Hydra Hydra generally refers to: * Lernaean Hydra, a many-headed serpent in Greek mythology * ''Hydra'' (genus), a genus of simple freshwater animals belonging to the phylum Cnidaria Hydra or The Hydra may also refer to: Astronomy * Hydra (constel ...

. Two

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

s have been confirmed to be orbiting it, and it is thought that the system had more giant planets that were "swallowed" by the parent star. HD 82943 is estimated at 1.15 times the mass of the Sun.

Planetary system

The first planet discovered (designated HD 82943 b) was announced in 2000 by a team of

French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...

astronomers led by

Michel Mayor Michel Gustave Édouard Mayor (; born 12 January 1942) is a Swiss astrophysicist and professor emeritus at the University of Geneva's Department of Astronomy. He formally retired in 2007, but remains active as a researcher at the Observatory ...

. The planet orbits its parent star at a mean distance of 1.19

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s (AU) and taking approximately 441

day A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours, 1440 minutes, or 86,400 seconds. In everyday life, the word "day" often refers to a solar day, which is the length between two so ...

s to complete the orbit. Nearly a year later, a second planet (designated HD 82943 c) was announced by the same discoverers of the previous planet. This planet orbits closer than the other, at a mean distance of 0.746 AU and taking 219 days to complete its orbit. The two known planets appear to have a 2:1

resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...

with one another. Further radial velocity analysis hinted at either long-period stellar activity or presence of a third Jovian planet with an orbital period of 1075 days. Announced in 2001, HD 82943 was found to contain an unusually high amount of

lithium-6 Naturally occurring lithium (3Li) is composed of two stable isotopes, lithium-6 and lithium-7, with the latter being far more abundant on Earth. Both of the natural isotopes have an unexpectedly low nuclear binding energy per nucleon ( for lit ...

. Stars do not naturally contain lithium-6, but unlike stars,

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

s never reach temperatures that are high enough to burn their initial content of lithium-6 (planets should retain lithium-6). The simplest and most convincing answer to explain this observation is that one or more planets, or at least planetary material, have fallen into the star, sometime after it passed through its early evolutionary stage.

References

External links

* * *
Extrasolar Planet Interactions
by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona {{DEFAULTSORT:HD 82943 F-type main-sequence stars 082943 047007 Hydra (constellation) Planetary systems with two confirmed planets Durchmusterung objects

Planetary system

See also

References

External links