  The ''radius valley" is a relative dearth of planets between two potential
populations of exoplanets, super-Earths and mini-Neptunes. This feature appears
in examining the distribution of planetary radii, but has only ever been
characterized on small samples. The valley could be a result of
photoevaporation, which has been predicted in numerous theoretical models, or a
result of other processes. Here, we investigate the relationship between
planetary radius and orbital period through 2-dimensional kernel density
estimator and various clustering methods, using all known super-Earths
($R<4.0R_E$). With our larger sample, we confirm the radius valley and
characterize it as a power law. Using a variety of methods, we find a range of
slopes that are consistent with each other and distinctly negative. We average
over these results and find the slope to be $m=-0.319^{+0.088}_{-0.116}$. We
repeat our analysis on samples from previous studies. For all methods we use,
the resulting line has a negative slope, which is consistent with models of
photoevaporation and core-powered mass loss but inconsistent with planets
forming in a gas-poor disk.
