Marcy and Butler had suspected that the star was unusual when they discovered its first planet in 1996, but couldn't study it more till 1999. The extra observed wobble could only be explained by the presence of a third planet. Those conclusions are supported by computer models, which show such a three-planet system is viable.
Astronomers are both elated and perplexed by the new discovery.
However, theories of planetary formation can't explain how three massive planets could exist so close to their star. But all three giant planets around Upsilon Andromedae now reside inside this theoretical ice boundary. A number of theories have been proposed to explain the existence of such massive planets, ranging from their formation close to a star to the migration of planets from the outer to the inner portions of the solar system .