  Using the Kepler planet sample from Buchhave et al. and the statistical
method clarified by Schlaufman, I show that the shorter-period super-Earths
have a different dependence on the host star metallicity from the longer-period
super-Earths, with the transition period being in the period range from 70 to
100 days. The hosts of shorter-period super-Earths are on average more
metal-rich than those of longer-period super-Earths. The existence of such a
transition period cannot be explained by any single theory of super-Earth
formation, suggesting that super-Earths have formed via at least two
mechanisms.
