HD 200964
Encyclopedia
HD 200964 is a 7th magnitude
star
located approximately 223 light-year
s away in the constellation
of Equuleus
. It is a K-type subgiant
with 44% more mass than the Sun
, but cooler. At the age of 3 billion years, it indicates that it is an evolved A-type star. At a magnitude
of 6.64, this star is too faint to be seen with the naked eye
for most people, but binoculars
would make it easy to see this star. Only people with a very clear eyesight and very dark sky can barely see this star.
The star is known to have two giant extrasolar planet
s.
. The inner planet is nearly twice as massive as Jupiter and takes 614 days to orbit the star in a circular orbit at the average distance of 1.60 AU (240 Gm). The outer planet is 9/10 the mass of Jupiter and takes 825 days to orbit eccentrically around the star at the average distance of 1.95 AU (292 Gm).
The two planets are in a 4:3 resonance
, meaning that every time the outer planet orbits the star three times, the inner planet orbits the star four times. The two planets are separated by only 0.35 AU (52 Gm). Because of the small separation between the two massive planets, the gravitational tugs between the two planets is merely 3 million times greater than the gravitational force between Earth and Mars, 700 times larger than that between Earth and the Moon, and 4 times larger than the pull of the Sun on Earth.
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...
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 approximately 223 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away 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 Equuleus
Equuleus
Equuleus is a constellation. Its name is Latin for 'little horse', a foal. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations. It is the second smallest of the modern constellations , spanning only 72 square degrees...
. It is a K-type subgiant
Subgiant star
A subgiant star is a star that is slightly brighter than a normal main-sequence star of the same spectral class, but not as bright as true giant stars...
with 44% more mass than 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...
, but cooler. At the age of 3 billion years, it indicates that it is an evolved A-type star. At a 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 6.64, this star is too faint to be seen with the naked eye
Naked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
for most people, but binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
would make it easy to see this star. Only people with a very clear eyesight and very dark sky can barely see this star.
The star is known to have two giant extrasolar planet
Extrasolar 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...
s.
Planetary system
On July 26, 2010 the California and Carnegie Planet Search team announced the discovery of two planets around HD 200964 along with two planets around 24 Sextantis24 Sextantis
24 Sextantis is a 7th magnitude star located approximately 244 light-years away in the constellation of Sextans. It is a G-type subgiant with 54% more mass than the Sun, but cooler. At the age of 2.7 billion years, it indicates that it is an evolved A-type star...
. The inner planet is nearly twice as massive as Jupiter and takes 614 days to orbit the star in a circular orbit at the average distance of 1.60 AU (240 Gm). The outer planet is 9/10 the mass of Jupiter and takes 825 days to orbit eccentrically around the star at the average distance of 1.95 AU (292 Gm).
The two planets are in a 4:3 resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
, meaning that every time the outer planet orbits the star three times, the inner planet orbits the star four times. The two planets are separated by only 0.35 AU (52 Gm). Because of the small separation between the two massive planets, the gravitational tugs between the two planets is merely 3 million times greater than the gravitational force between Earth and Mars, 700 times larger than that between Earth and the Moon, and 4 times larger than the pull of the Sun on Earth.