HR 7722
Encyclopedia
HR 7722 is a star
in the constellation
Capricornus
. It is located in the solar neighborhood at a distance of just over 29 light years, and is within the range of luminosity needed to be viewed from the Earth with the unaided eye. HR 7722 is suspected of being a variable star
, but this is unconfirmed.
HR 7722 has about 78% of the Sun's mass
and, depending on the estimation method, 79% to 85% of the radius of the Sun. It is older than the Sun, with age estimates in the range 7.5–8.9 billion years. The proportion of elements other than hydrogen
and helium
, known as the metallicity
, is similar to that of the Sun.
The space velocity components of this star are (U, V, W) = . It is following an orbit through the Milky Way
galaxy that has an orbital eccentricity
of 0.18 at a mean galactocentric distance of 8.1 kpc
.
-mass planet "b
", discovered in 2010. A second planet "c
" was found in this system in 2011 by the HARPS GTO program. The uncertainty in the mass of the second planet is much higher than for the first because of the lack of coverage around the full orbit. Both planets may be similar in composition to Neptune. They are orbiting along the inner and outer edges of the habitable zone
for this 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....
Capricornus
Capricornus
Capricornus is one of the constellations of the zodiac; it is often called Capricorn, especially when referring to the corresponding astrological sign. Its name is Latin for "horned male goat" or "goat horn", and it is commonly represented in the form of a sea-goat: a mythical creature that is half...
. It is located in the solar neighborhood at a distance of just over 29 light years, and is within the range of luminosity needed to be viewed from the Earth with the unaided eye. HR 7722 is suspected of being a variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
, but this is unconfirmed.
HR 7722 has about 78% 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, depending on the estimation method, 79% to 85% of the radius of the Sun. It is older than the Sun, with age estimates in the range 7.5–8.9 billion years. The proportion of elements other than hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, known as the 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 similar to that of the Sun.
The space velocity components of this star are (U, V, W) = . It is following 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 orbital eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of 0.18 at a mean galactocentric distance of 8.1 kpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
.
Planetary system
The system has a NeptuneNeptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
-mass planet "b
HR 7722 b
HR 7722 b is an extrasolar planet orbiting the star HR 7722....
", discovered in 2010. A second planet "c
HR 7722 c
HR 7722 c is an extrasolar planet orbiting the star HR 7722....
" was found in this system in 2011 by the HARPS GTO program. The uncertainty in the mass of the second planet is much higher than for the first because of the lack of coverage around the full orbit. Both planets may be similar in composition to Neptune. They are orbiting along the inner and outer edges of the habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
for this star.