HD 200964 is a 7th magnitude star located approximately 223 light-years 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 planets.
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 Sextantis. 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.
* 24 Sextantis
1. ^ a b "Astronomers find planets in unusually intimate dance around dying star". Astronomy Magazine. July 29, 2010. http://www.astronomy.com/en/News-Observing/News/2010/07/Astronomers%20find%20planets%20in%20unusually%20intimate%20dance%20around%20dying%20star.aspx. Retrieved 2011-01-13.