Upsilon Andromedae

υ Andromedae was the first main sequence star determined to have more than one extrasolar planet. So far, three planets have been discovered within the system; all three are believed to be gas giants.

Extrasolar planets

υ Andromedae b is a gas giant that orbits extremely close to the star.
:* Distance from the star: 0.06 AU
:* Minimum mass: 0.71 M_J
:* Orbital period: 4.6 days

υ Andromedae c is a gas giant with twice the mass of Jupiter that orbits closer to the star than Earth is to the Sun.
:* Distance from the star: 0.83 AU
:* Minimum mass: 2.11 M_J
:* Orbital period: 242 days

υ Andromedae d is a large gas giant 4 times the mass of Jupiter. It has an eccentric orbit within the star's habitability zone.
:* Distance from the star: 2.5 AU
:* Minimum mass: 4.61 M_J
:* Orbital period: 3.5 years

History of discovery

The innermost planet (b) was discovered in 1996 and announced in January of 1997 by Geoffrey Marcy and R. Paul Butler, both astronomers at San Francisco State University (SFSU). Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. However, some additional wobble in the star remained unexplained, and it was suggested there might be a second planet in orbit. In the end, astronomers at both SFSU and the Harvard-Smithsonian Center for Astrophysics independently concluded that, in fact, a three-planet model best fit the data. These results were announced on April 15, 1999.

The existence of further planets too small to detect has not been ruled out.

See also