  The solar system and the hydrogen atom are two well known systems on
different scales and look unrelated: The former is a classical system on the
scale of about billions of kilometers and the latter a quantum system of about
tens of picometers. Here we show a connection between them. Specifically, we
find that the orbital radii of the planets mimic the mean radii of the energy
levels of a quantum system under the Coulomb-like potential. This connection
might be explained by very light dark matter which manifests quantum behavior
in the solar system, thereby hinting at a dark matter mass around $8 \times
10^{-14}$ electron-volts.
