Because of their large numbers , low mass stars may be the most abundant planet hosts in our Galaxy .
Furthermore , terrestrial planets in the habitable zones ( HZs ) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied .
Recently ( 11 ) used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15 ^ { +0.13 } _ { -0.06 } per star for Earth-size planets ( 0.5 - 1.4 R _ { \oplus } ) .
However , this estimate was derived using the ( 21 ) HZ limits , which were not valid for stars with effective temperatures lower than 3700 K. Here we update their result using new HZ limits from ( 23 ) for stars with effective temperatures between 2600 K and 7200 K , which includes the cool M stars in the Kepler target list .
The new habitable zone boundaries increase the number of planet candidates in the habitable zone .
Assuming Earth-size planets as 0.5 - 1.4 R _ { \oplus } , when we reanalyze their results , we obtain a terrestrial planet frequency of 0.48 ^ { +0.12 } _ { -0.24 } and 0.53 ^ { +0.08 } _ { -0.17 } planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries , respectively .
Assuming Earth-size planets as 0.5 - 2 R _ { \oplus } , the frequency increases to 0.51 ^ { +0.10 } _ { -0.20 } per star for the conservative estimate and to 0.61 ^ { +0.07 } _ { -0.15 } per star for the optimistic estimate .
Within uncertainties , our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs ( 0.41 ^ { +0.54 } _ { -0.13 } , ( 6 ) ) .
So , the potential for finding Earth-like planets around M stars may be higher than previously reported .