  The observational signatures of prominences have been detected in single and
binary G and K type stars for many years now, but recently this has been
extended to the M dwarf regime. Prominences carry away both mass and angular
momentum when they are ejected and the impact of this mass on any orbiting
planets may be important for the evolution of exoplanetary atmospheres. By
means of the classification used in the massive star community, that involves
knowledge of two parameters (the co-rotation and Alfv\'en radii, $r_K$ and
$r_A$), we have determined which cool stars could support prominences. From a
model of mechanical support, we have determined that the prominence mass
$m_p/M_\star=(E_M/E_G)(r_\star/r_K)^2 F$ where $E_MB_\star^2r_\star^3$ and $E_G
= GM_\star^2/r_\star$ are magnetic and gravitational energies and $F$ is a
geometric factor. Our calculated masses and ejection frequencies (typically
$10^{16}-10^{17}$g and 0.4 d, respectively) are consistent with observations
and are sufficient to ensure that an exoplanet orbiting in the habitable zone
of an M dwarf could suffer frequent impacts.
