Gliese 229 (also written as Gl 229 or GJ 229) is a binary system composed of a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

and the first

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

seen by astronomers, 18.8

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 ...

Lepus Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores, and live solitarily or in pairs. They nest in slight depressions called forms, and their young are able to fend for themselves shortly after birth. The gen ...

. The primary component has 58% of the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s at the stellar equator. The star is known to be a low activity

flare star A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to the magnetic energy stored in th ...

, which means it undergoes random increases in luminosity because of

magnetic activity A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magn ...

at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s has been detected from the

corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...

of this star. These may be caused by magnetic loops interacting with the gas of the star's outer atmosphere. No large-scale star spot activity has been detected. The space velocity components of this star are U = +12, V = –11 and W = –12 km/s. The orbit of this star through the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy has an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...

of 0.07 and an orbital

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of 0.005.

Companions

Brown dwarf

substellar companion A substellar object, sometimes called a substar, is an astronomical object the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and fo ...

was discovered in 1994 by Caltech astronomers Kulkarni, Tadashi Nakajima, Keith Matthews, and

Rebecca Oppenheimer Rebecca Oppenheimer is an American astrophysicist and one of four curator/professors in the Department of Astrophysics at the American Museum of Natural History (AMNH) on Manhattan's Upper West Side. Oppenheimer is a comparative exoplanetary sci ...

, and Johns Hopkins scientists Sam Durrance and David Golimowski. It was confirmed in 1995 as Gliese 229B, one of the first two instances of clear evidence for a

, along with

Teide 1 Teide 1 was the first brown dwarf to be verified, in 1995. It is located in the Pleiades open star cluster, approximately from Earth. This object is more massive than a planet (), but less massive than a star (0.0544 MSun). The radius ...

. Although too small to sustain

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

-burning

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...

as in 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 Her ...

star, with a mass of around 40 to 60 times that of

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 mass more than two and a half times that of all the other planets in the Solar System combined, but ...

(0.06 solar masses), it is still too massive to be a

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 ...

. As a brown dwarf, its core temperature is high enough to initiate the fusion of

deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...

with a proton to form

helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the ...

, but it is thought that it used up all its deuterium fuel long ago. This object has a surface temperature of 950 K. The most recent parameters for Gliese 229 B as of 2022 come from a combination of data from

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. His ...

, and imaging, showing that it is about 60.4 times the mass of Jupiter, and on an

eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...

orbit with a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of about 28.9 AU and an orbital period of about 217 years.

Planetary system

In March 2014, a

super-Neptune A super-Neptune is a planet that is more massive than the planet Neptune. These planets are generally described as being around 5–7 times as large as Earth with estimated masses of 20–80 ; beyond this they are generally referred to as gas gian ...

mass planet candidate was announced in a much closer-in orbit around GJ 229. Given the proximity to the Sun, the orbit of GJ 229 Ab might be fully characterized by the

Gaia In Greek mythology, Gaia (; from Ancient Greek , a poetical form of , 'land' or 'earth'),, , . also spelled Gaea , is the personification of the Earth and one of the Greek primordial deities. Gaia is the ancestral mother—sometimes parthenog ...

space-astrometry mission or via direct imaging. In 2020, a

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 ...

mass planet was discovered around GJ 229. GJ 229 Ac orbits the star closer in than GJ 229 Ab, located towards the outer edge but still well inside the star's

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

and in that sense similar to

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

in our own

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

. While considering GJ 229 Ab an unconfirmed candidate, the study estimated a significantly lower

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

for it. , most sources consider both planets to be confirmed. If the planets Gliese 229 Ab & c orbit in the same plane as the brown dwarf Gliese 229 B, their true masses would be significantly greater than their

es, making them both

s nearly as massive as

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 nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

./sin(5.497°) =
/sin(5.497°) =

References

Notes

External links

Brown dwarfs (NASA)
{{DEFAULTSORT:Gliese 229 Binary stars Flare stars 0229 Lepus (constellation) M-type main-sequence stars T-type stars 042581 ? Durchmusterung objects 029295 Planetary systems with two confirmed planets TIC objects