For the past few decades, our understanding of structure formation on sub-galactic scales has been thought to have several outstanding issues, including the “missing satellites problem.” In the advent of improved sensitivity to faint satellites with galaxy surveys, as well as purely gravitational probes of dark low-mass sub-halos, it appears that there is no missing satellites problem and the satellites predicted by the cold dark matter paradigm have been found. In this talk, I will describe these advances on the astro side and will discuss the implications for two types of particle dark matter models: (1) IR-dominated freeze-in and (2) ultralight scalars. Existing and upcoming probes of low-mass halos, in combination with terrestrial experiments, will be able to discover or exclude entire broad classes of qualitatively distinct dark matter behaviour: (1) that dark matter was made from decaying light in the early Universe and (2) that dark matter behaves like a classical wave on galactic scales.