  The nature of dark matter (DM) is unknown. One compelling possibility is DM
being composed of primordial black holes (PBHs), given the tight limits on some
types of elementary particles as DM. There is only one remaining window of
masses available for PBHs to constitute the entire DM density, $10^{17} -
10^{23} \mathrm{\; g}$. Here, we show that the kernel population in the cold
Kuiper belt rules out this window, arguing in favor of a particle nature for
DM.
