Upsilon Andromedae c

Upsilon Andromedae c is an extrasolar planet orbiting the Sun-like star Upsilon Andromedae A every 241.2 days. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first known star (excluding the pulsar PSR 1257+12) to host a multiple-planet planetary system. Upsilon Andromedae c is the second known planet in order of distance from its star.
==Discovery==
Like the majority of known extrasolar planets, Upsilon Andromedae c was detected by measuring variations in its star's radial velocity as a result of the planet's gravity. This was done by making precise measurements of the Doppler shift of the spectrum of Upsilon Andromedae A. At the time of discovery, Upsilon Andromedae A was already known to host one extrasolar planet, the hot Jupiter Upsilon Andromedae b, however by 1999 it was clear that the inner planet could not explain the velocity curve.
In 1999, astronomers at both San Francisco State University and the Harvard-Smithsonian Center for Astrophysics independently concluded that a three-planet model best fit the data. The two new planets were designated Upsilon Andromedae c and Upsilon Andromedae d.
==Orbit and mass==
Like the majority of long-period extrasolar planets, the orbit of Upsilon Andromedae c is eccentric, more so than any of the major planets in our solar system (including Pluto). (web version) If placed in our solar system, Upsilon Andromedae c would lie between the orbits of Earth and Venus.
The high orbital eccentricity may be the result of gravitational perturbations from the planet Upsilon Andromedae d. Simulations suggest that the orbit of Upsilon Andromedae c returns to its original circular state roughly once every 6,700 years.
One proposal is that interactions between Upsilon Andromedae d and a (now lost) outer planet moved Upsilon Andromedae d into an orbit closer to the star, where it gradually caused the orbit of Upsilon Andromedae c to become eccentric. If so, the rogue planet would have had to eject immediately; it is unclear how likely this situation might be. Other models are possible.
A limitation of the radial velocity method used to detect Upsilon Andromedae c is that the orbital inclination is unknown, and only a lower limit on the planet's mass can be obtained. However, by combining radial velocity measurements from ground-based telescopes with astrometric data from the Hubble Space Telescope, astronomers have determined the orbital inclination as well as the actual mass of Upsilon Andromedae c, which is about 13.98 times the mass of Jupiter. The mutual inclination between c and d is 29.9 degrees.
==Characteristics==
Given the planet's high mass, it is likely that Upsilon Andromedae c is a gas giant with no solid surface. Since the planet has only been detected indirectly through observations of its star, properties such as its radius, composition, and temperature are unknown.
==References==
==See also==
* Eccentric Jupiter
Category:Upsilon Andromedae
Category:Exoplanets discovered in 1999
Category:Gas giants
Category:Exoplanets detected by radial velocity