<P> Red giants with known planets: the M - type HD 208527, HD 220074 and, as of February 2014, a few tens of known K - giants including Pollux, Gamma Cephei and Iota Draconis . </P> <P> Although traditionally it has been suggested the evolution of a star into a red giant will render its planetary system, if present, uninhabitable, some research suggests that, during the evolution of a 1 M star along the red - giant branch, it could harbor a habitable zone for several times 10 years at 2 AU out to around 10 years at 9 AU out, giving perhaps enough time for life to develop on a suitable world . After the red - giant stage, there would for such a star be a habitable zone between 7 and 22 AU for an additional 10 years . Later studies have refined this scenario, showing how for a 1 M star the habitable zone lasts from 10 years for a planet with an orbit similar to that of Mars one to 7015662709600000000 ♠ 2.1 × 10 yr for one that orbits at Saturn's distance to the Sun, the maximum time (7016116763120000000 ♠ 3.7 × 10 yr) corresponding for planets orbiting at the distance of Jupiter . However, for planets orbiting a 0.5 M star in equivalent orbits to those of Jupiter and Saturn they would be in the habitable zone for 7017183034080000000 ♠ 5.8 × 10 yr and 7016662709600000000 ♠ 2.1 × 10 yr respectively; for stars more massive than the Sun, the times are considerably shorter . </P> <P> As of June 2014, 50 giant planets have been discovered around giant stars . However, these giant planets are more massive than the giant planets found around solar - type stars . This could be because giant stars are more massive than the Sun (less massive stars will still be on the main sequence and will not have become giants yet) and more massive stars are expected to have more massive planets . However, the masses of the planets that have been found around giant stars do not correlate with the masses of the stars; therefore, the planets could be growing in mass during the stars' red giant phase . The growth in planet mass could be partly due to accretion from stellar wind, although a much larger effect would be Roche lobe overflow causing mass - transfer from the star to the planet when the giant expands out to the orbital distance of the planet . </P> <P> Many of the well known bright stars are red giants, because they are luminous and moderately common . The asymptotic giant branch variable star Gamma Crucis is the nearest M class giant star at 88 light years . The K0 red giant branch star Arcturus is 36 light years away . </P>

How are red giants different from main sequence stars