Population I

Population I stars

Population I stars usually have regular elliptical orbits of the Galactic Center, with a low relative velocity. It was earlier hypothesized that the high metallicity of population I stars makes them more likely to possess planetary systems than the other two populations, because planets, particularly terrestrial planets, are thought to be formed by the accretion of metals. However, observations of the Kepler Space Telescope data have found smaller planets around stars with a range of metallicities, while only larger, potential gas giant planets are concentrated around stars with relatively higher metallicity – a finding that has implications for theories of gas-giant formation. Between the intermediate population I and the population II stars comes the intermediate disc population.