Gliese 176
Encyclopedia
Gliese 176 is a red dwarf
star
in the constellation
of Taurus
. Based upon parallax
measurements from the Hipparcos
mission, it is located approximately 31 light years away. It has half the mass of the Sun
, 53% of the Sun's radius and an apparent magnitude
of +9.97.
The corona
of this star has a moderate emission of X-ray
s at . This indicates the star is active, and may exhibit starspots and flares much like the Sun. This is considered normal for a main sequence
star of spectral class M. The proportion of elements with atomic numbers higher than helium (or metallicity
) is also similar to that of the Sun.
The space velocity components of this star are U = –26, V = –63 and W = –14 km/s.
. This was based upon a five year program of radial velocity
measurements at the Hobby-Eberly telescope
. The estimated lower bound for the planet's mass was 24.5 times the mass of the Earth, or 0.0771 times the mass of Jupiter
. The orbital period
of the planet is 10.24 days. Rotational modulation due to star spots was deemed unlikely as the star is thought unlikely to rotate that rapidly.
A subsequent four-year study of the star showed that the original detection may have been spurious. Instead, strong evidence was detected of a planet with a lower bound of 8.4 times the mass of the Earth. The signal indicated an orbital period of 8.78 days and a semi-major axis
of 0.066 AU
. The thermal equilibrium temperature at that distance is 450 K
. Most of the planet's mass is likely to be rock, but it may have acquired a gas atmosphere.
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
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...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Taurus
Taurus (constellation)
Taurus is one of the constellations of the zodiac. Its name is a Latin word meaning 'bull', and its astrological symbol is a stylized bull's head:...
. Based upon parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...
measurements from the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
mission, it is located approximately 31 light years away. It has half the mass of the Sun
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
, 53% of the Sun's radius and an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of +9.97.
The corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
of this star has a moderate emission of X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s at . This indicates the star is active, and may exhibit starspots and flares much like the Sun. This is considered normal for 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 class M. The proportion of elements with atomic numbers higher than helium (or 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...
) is also similar to that of the Sun.
The space velocity components of this star are U = –26, V = –63 and W = –14 km/s.
Planetary system
In 2008 it was announced that this star had a planetary companionExtrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
. This was based upon a five year program of radial velocity
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...
measurements at the Hobby-Eberly telescope
Hobby-Eberly Telescope
The Hobby-Eberly Telescope is a 9.2-meter aperture telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs...
. The estimated lower bound for the planet's mass was 24.5 times the mass of the Earth, or 0.0771 times the mass of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. The orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of the planet is 10.24 days. Rotational modulation due to star spots was deemed unlikely as the star is thought unlikely to rotate that rapidly.
A subsequent four-year study of the star showed that the original detection may have been spurious. Instead, strong evidence was detected of a planet with a lower bound of 8.4 times the mass of the Earth. The signal indicated an orbital period of 8.78 days and a semi-major axis
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
of 0.066 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
. The thermal equilibrium temperature at that distance is 450 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
. Most of the planet's mass is likely to be rock, but it may have acquired a gas atmosphere.