The authors of this paper suggest that the peculiar orbits of Trans-Neptunian Objects (TNOs) and an excess of microlensing events in the OGLE dataset can both be explained by the existence of a new population of astrophysical bodies with a mass several times that of Earth. They propose that these objects are primordial black holes (PBHs) and argue that the capture of a PBH by the Solar System could account for the hypothesized ninth planet (Planet 9). They point out that the probability of capturing a PBH is comparable to that of capturing a free-floating planet. The presence of a PBH in the outer Solar System would have different observable effects than a ninth planet, and this scenario could potentially be confirmed through the detection of annihilation signals from the dark matter microhalo around the PBH.
https://arxiv.org/abs/1909.11090