HD 219134 (also known as Gliese 892 or HR 8832) is a

main-sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hert ...

star 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 ...

of Cassiopeia. It is smaller and less luminous than the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, with a

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of K3V, which makes it an orange-hued star. HD 219134 is relatively close to our system, with an estimated distance of 21.34

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. This star is close to the limit of

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

that can still be seen by the unaided eye. The limit is considered to be magnitude 6 for most observers. This star has a magnitude 9.4 optical companion at an angular separation of 106.6

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

Planetary system

HD 219134 has a system of six known

exoplanet 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. The innermost planet,

HD 219134 b HD 219134 b (or HR 8832 b) is one of at least five exoplanets orbiting HD 219134, a main-sequence star in the constellation of Cassiopeia. HD 219134 b has a size of about 1.6 , and a density of 6.4 g/cm3 and orbits at 21.25 light-years away. ...

, is a rocky

super-Earth A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to ...

based on size (1.6 times the size of Earth), and density (6.4 grams per cubic cm). This and three additional exoplanets; one

(designated ''c'' and later found to be rocky as well), one

Neptunian Neptune was discovered in 1846 and has only made occasional appearances in fiction since then. The first time it was mentioned, then called "Urbain Le Verrier, Leverrier's planet", was in the 1848 novel ''The Triumphs of Woman'' by Charles Rowcrof ...

world (''d''), and one

Jovian Jovian is the adjectival form of Jupiter and may refer to: * Jovian (emperor) (Flavius Iovianus Augustus), Roman emperor (363–364 AD) * Jovians and Herculians, Roman imperial guard corps * Jovian (lemur), a Coquerel's sifaka known for ''Zoboomafo ...

world (''e''); were deduced using HARPS-N radial velocity data by Motalebi ''et al.'' in 2015. Two months later, Vogt ''et al.'' published a paper on this system which found a 6-planet solution, with planets ''b'', ''c'' & ''d'' corresponding to those in Motalebi ''et al.'', ''f'' & ''g'' being new planets, and ''h'' corresponding to Motalebi's ''e'' but with different, and more accurate, estimated parameters. A number of independent studies have been done regarding the planetary system of HD 219134, with some of their results conflicting with each other. As of March 2017, the star is known to have at least 5 planets, with two of them (HD 219134 b and c) known to be transiting, rocky super-Earths. While a 2016 study suggested that the radial velocity signal corresponding to planet ''f'' might be caused by stellar activity, it has been confirmed by subsequent studies in 2017 and 2021. Planet ''g'' has not been reported by subsequent studies, and a 2020 study did not find evidence of its claimed 94-day period, but instead found a period of 192 days.

Habitable Zone

The conservative habitable zone (CHZ) of HD 219134 is estimated to extend from 0.516 to 0.948 AU. None of the planets orbiting the star are confirmed to orbit inside the habitable zone. The planet candidate HD 219134 g may orbit slightly interior to the inner edge of the habitable zone based on its initially published parameters, or may orbit within the habitable zone based on a more recent estimated orbital period of 192 days and semi-major axis of 0.603 AU. This planet is significantly more massive than Earth and therefore it likely retains a dense atmosphere, comparable to the Solar System's

ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary science t ...

References

External links

* {{Sky, 23, 13, 16.98, +, 57, 10, 06.1, 100000 Cassiopeia (constellation) 0892 K-type main-sequence stars Gliese, 0892 Suspected variables 219134 8832 114622 Durchmusterung objects Planetary systems with six confirmed planets Planetary transit variables