18 Scorpii
Encyclopedia
18 Scorpii is a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 located some 45.3 light years 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...

 at the northern edge of the Scorpius constellation
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...

.

18 Scorpii has many physical properties in common with 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...

. Cayrel de Strobel (1996) included it in her review of the stars most similar to the Sun, and Porto de Mello & da Silva (1997) identified it as a solar twin. Some scientists therefore believe the prospects for life
Life
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...

 in its vicinity are good.

Star characteristics

18 Scorpii is a 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...

 star of spectral and luminosity type
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...

 G2 Va. Sousa et al (2008) found its metallicity
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...

 to be about 1.1 times that of the Sun, which means the abundance of elements other than hydrogen or helium is 110% greater. The radius of this star, as measured using interferometry
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....

 by Bazot et al (2011), is 101% the radius of the Sun. When combined with the results of astroseismology measurements, this allows the mass of the star to be estimated as 102% 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...

.

According to Lockwood (2002), it has a temporal photometric behavior very similar to the Sun. Its brightness variation over its entire activity cycle is 0.09%, about the same as the Sun's brightness variations during recent solar cycles. Using the technique of Zeeman-Doppler imaging
Zeeman-Doppler imaging
In astrophysics, Zeeman–Doppler imaging is a tomographic technique dedicated to the cartography of stellar magnetic fields.This method makes use of the ability of magnetic fields to polarize the light emitted in spectral lines formed in the stellar atmosphere...

, Petit et al. (2008) have detected its surface magnetic field, showing that its intensity and geometry are very similar to the large-scale solar magnetic field. The estimated period for the activity cycle of 18 Scorpii is about seven years, which is significantly shorter than the Sun's, and its overall chromospheric activity level is noticeably higher.

18 Scorpii is a solitary star, and radial velocity measurements have not yet revealed the presence of planets orbiting it.

Though 18 Scorpii is only slightly more metal-rich overall than the Sun, its lithium abundance is about three times as high; for this reason, Meléndez & Ramírez (2007) have suggested that 18 Scorpii be called a "quasi solar twin", reserving the term solar twin for stars (such as HIP 56948
HIP 56948
HIP 56948 is a solar twin star of type G5V, which as of March 2011, is the most sun-like star yet discovered in terms of size, mass, temperature, chemical makeup and, arguably, age...

) that match the Sun, within the observational errors, for all parameters.

Prospects for life

18 Scorpii was identified in September 2003 by astrobiologist Margaret Turnbull
Margaret Turnbull
Margaret Carol Turnbull is an American astronomer. She received her PhD in Astronomy from the University of Arizona in 2004. Turnbull is an authority on "Habstars," solar twins and planetary habitability....

 from the University of Arizona
University of Arizona
The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...

 in Tucson as one of the most promising nearby candidates for hosting life based on her analysis of the HabCat
HabCat
The Catalog of Nearby Habitable Systems is a catalogue of star systems which conceivably have habitable planets. The list was developed by scientists Jill Tarter and Margaret Turnbull under the auspices of Project Phoenix, a part of SETI....

list of stars.

External links

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