We confirm and characterize the exoplanetary systems Kepler -445 and Kepler -446 : two mid-M dwarf stars , each with multiple , small , short-period transiting planets . Kepler -445 is a metal-rich ( [ Fe/H ] =+0.25 \pm 0.10 ) M4 dwarf with three transiting planets , and Kepler -446 is a metal-poor ( [ Fe/H ] =-0.30 \pm 0.10 ) M4 dwarf also with three transiting planets . Kepler -445c is similar to GJ 1214b : both in planetary radius and the properties of the host star .
The Kepler -446 system is similar to the Kepler -42 system : both are metal-poor with large galactic space velocities and three short-period , likely-rocky transiting planets that were initially assigned erroneously large planet-to-star radius ratios .
We independently determined stellar parameters from spectroscopy and searched for and fitted the transit light curves for the planets , imposing a strict prior on stellar density in order to remove correlations between the fitted impact parameter and planet-to-star radius ratio for short-duration transits .
Combining Kepler -445 , Kepler -446 and Kepler -42 , and isolating all mid-M dwarf stars observed by Kepler with the precision necessary to detect similar systems , we calculate that 21 ^ { +7 } _ { -5 } % of mid-M dwarf stars host compact multiples ( multiple planets with periods of less than 10 days ) for a wide range of metallicities .
We suggest that the inferred planet masses for these systems support highly efficient accretion of protoplanetary disk metals by mid-M dwarf protoplanets .