The obscure Planet Nine

Planet Nine is an hypothetical plante in Our Souls System. Its existence is inferred by the orbital data of a group of extreme trans-Neptunian objects, that seemed influenced by the presence of an undiscovered planet, or something else. Recently Amir Siraj and Abraham Loeb proposed a new hypothesys: Planet Nine could be a little black hole, about five times more massive than Earth with the dimension of an orange:

Planet Nine has been proposed to potentially be a black hole in the outer solar system. We investigate the accretion flares that would result from impacts of small Oort cloud objects, and find that the upcoming LSST observing program will be able to either rule out or confirm Planet Nine as a black hole within a year. We also find that LSST could rule out or confirm the existence of trapped planet-mass black holes out to the edge of the Oort cloud, indirectly probing the dark matter fraction in subsolar mass black holes and potentially improving upon current limits by orders of magnitude.

Siraj, A., & Loeb, A. (2020). Searching for Black Holes in the Outer Solar System with LSST. ApJL 898 L4 arXiv:2005.12280. doi:10.3847/2041-8213/aba119 (arXiv).