Marcy and Butler had suspected that the star was unusual when they discovered the first planet around it in 1996, but didn't have enough data until this year to study it in further detail. They were able to fit a second planet to the variations in wavelength of light from the star, caused by the Doppler effect as the planet's gravity tugs on the star, but weren't satisfied. We arrived at the conclusion that 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 such massive planets could exist so close to their parent star. This will shake up the theory of planet formation. Robert Noyes of the Harvard-Smithsonian Center of Astrophysics, part of a group that independently discovered the two new planets, said the discovery confirms that the objects seen are planets and not more massive brown dwarfs. 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.