Alien planet. Artwork of the Upsilon Andromedae b planet (at upper right) orbiting the Upsilon Andromedae star (at lower left). Gases in the planet's atmosphere are streaming from the point near the Sun to the far side. Upsilon Andromedae b has a mass which is at least 60% of that of Jupiter and orbits the star in 4.61 days. One side of the planet may always face the star. This is because the star's mass most strongly attracts the heaviest part of the planet and stops it from spinning. This planet was discovered by Geoff Marcy and Paul Butler.