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Upsilon Andromedae (or υ Andromedae) is a star, approximately 44 light-years from Earth, and approximately 3 billion years old, two thirds the age of our Sun. Viewed from Earth, Upsilon Andromedae is in the Andromeda Constellation, and is about 10 degrees east of the Andromeda Galaxy.
Upsilon Andromedae was the first main sequence star determined to have more than one extrasolar planet. So far, three such objects have been discovered within the system; all three are believed to be gas giants.
Extrasolar planets
Upsilon Andromedae b is a gas giant that orbits extremely close to the star. It is probably so hot that it glows red. [1] (http://www.extrasolar.net/planettour.asp?StarCatId=&PlanetId=3)
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Upsilon Andromedae c is a gas giant with twice the mass of Jupiter that orbits closer to the star than Earth is to the Sun. Its composition and position means that it would be blue in colouring.
- Distance from UA: 0.83AU
- Mass: 2.11 MJ
- Orbital Period: 242 days
Upsilon Andromedae d is a large gas giant of 4 times the mass of Jupiter. It has an eccentric orbit within the star's habitability zone.
- Distance from UA: 2.5AU
- Mass: 4.61 MJ
- Orbital Period: 3.5 years
History of discovery
The inner 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 3-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
External links
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