Photon-limited transit surveys in V band are in principle about 20 times more sensitive to planets of fixed size in the habitable zone around M stars than G stars .
In I band the ratio is about 400 .
The advantages that the habitable zone lies closer and that the stars are smaller ( together with the numerical superiority of M stars ) more than compensate for the reduced signal due to the lower luminosity of the later-type stars .
That is , M stars can yield reliable transit detections at much fainter apparent magnitudes than G stars .
However , to achieve this greater sensitivity , the later-type stars must be monitored to these correspondingly fainter magnitudes , which can engender several practical problems .
We show that with modest modifications , the Kepler mission could extend its effective sensitivity from its current M _ { V } = 6 to M _ { V } = 9 .
This would not capture the whole M dwarf peak , but would roughly triple its sensitivity to Earth-like planets in the habitable zone .
However , to take advantage of the huge bump in the sensitivity function at M _ { V } = 12 would require major changes .