Zeta Reticuli
Encyclopedia
Zeta Reticuli is a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 system located about 39 ly away from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. It is located in the constellation Reticulum
Reticulum
Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions...

, and is visible to the unaided eye in very dark skies. Because of the southerly location of the system, it is not visible north of the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

.

Characteristics

This system consists of a pair of stars that are both similar in physical characteristics to the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. Their stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 is nearly identical to the Sun, and they are considered solar analog
Solar analog
Solar-type, solar analog, and solar twin stars are those stars that are particularly similar to the Sun. The classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type...

s. ζ1 has 96% of the Sun's mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

 and 84% of the Sun's radius. ζ2 is slightly larger and more luminous than ζ1, with 99% of the Sun's mass and 88% of the Sun's radius.

The two stars are somewhat deficient in metals
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...

, having only 60% of the proportion of elements other than hydrogen and helium compared to the Sun. For reasons that remain uncertain, they have an anomalously low abundance of beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

. Both stars are considered unusual because they have a lower luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...

 than is normal for main sequence
Main sequence
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 Hertzsprung and Henry Norris Russell...

 stars of their age and surface temperature. That is, they lie below the main sequence curve on the Hertzsprung-Russell diagram for newly formed stars. Most stars will evolve above this curve as they age.

ζ1 has an intermediate level of magnetic activity in its chromosphere
Chromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....

. Although the kinematics of this system suggest that they belong to a population of older stars, the properties of their stellar chromosphere
Chromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....

s suggests that they are only about 2 billion years old.

On September 20, 1996, a tentative discovery of a hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...

 around ζ2 was reported, but the discovery was quickly retracted as the signal was shown to be caused by pulsations of the star. In 2002, ζ1 was examined at an infrared wavelength of 25 μm, but no indication of an excess of infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 radiation was found. In 2007, the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...

 was used to find an infrared excess at a wavelength of 70 μm around ζ2. This radiation is likely being emitted by a debris disk
Debris disk
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a...

 with a mean temperature of 150 K (-123.2 °C) that is orbiting the host star at a distance of 4.3 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

. In 2010, the Herschel Space Observatory
Herschel Space Observatory
The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....

, looking for debris disks analogous to the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...

, around sun like stars, detected signs of a possible exo-kuiper belt, with a semi-major axis of 100 AU around ζ2.

Both stars share similar proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...

s, radial velocities
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...

 and distances, confirming that they form a wide binary star system. The stars have an angular separation of 309.2 arc seconds (5.2 arc minutes); far enough apart to appear as a close pair of separate stars to the naked eye with a dark sky. The distance between the two stars is about 3,750 AU.

This star system belongs to the Zeta Herculis Moving Group
Zeta Herculis Moving Group
Zeta Herculis Moving Group is a set of stars that share a common motion through space.The existence of this moving group was first published in 1958 by Olin J. Eggen. Based upon the high velocity motion of the star Zeta Herculis through space, he searched for stars that were following a similar...

 of stars with common motions through space. The space velocity components of this system are = (−70.2/−69.7, −47.4/−46.4, +16.4/+16.8) km/s. They are currently on an orbit through the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 galaxy that has an eccentricity of 0.24. This orbit will carry the system as close as 17.4 kly and as far as 28.6 kly from the galactic core. The inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...

 of this orbit will carry the stars as much as 1.3 kly from the plane of the galactic disk. This likely puts them outside the thick disk population of stars.

See also

  • Zeta Reticuli in fiction
  • Role of Zeta reticuli in the story of the purported Betty and Barney Hill abduction
    Betty and Barney Hill abduction
    Betty and Barney Hill were an American couple who claimed to have been abducted by extraterrestrials in a rural portion of New Hampshire on September 19–20, 1961....

     by space alien
    Extraterrestrial life
    Extraterrestrial life is defined as life that does not originate from Earth...

    s (Greys)
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