Alien planet and its sun. Artwork of the planet HD 209458 b with its parent star (HD 209458), as seen from the surface of a moon. This planet was detected as it transited (passed in front of) its star, causing a dip in brightness of 1.7%, at the time predicted from orbital calculations. This was the first direct evidence of a planet orbiting another star when it was first observed in 1999. The presence of the planet was detected by observing the wobble its orbit had on the star's motion through space. HD 209458 B is about 200 times the mass of Earth, but orbits only 6.5 million kilometres from its star, where one orbit takes just 3.5 days. HD 209458 is a Sun-like star (yellow dwarf) that lies 153 light years from Earth, in the constellation Pegasus.