And at 5M⊕ would have a diameter of about 9cm (or at 10M⊕ about the size of a bowling ball).
Do we stand a chance of uncovering it at all?
Edit: from the abstract,
> The observational constraints on a PBH in the outer Solar System significantly differ from the case of a new ninth planet. This scenario could be confirmed through annihilation signals from the dark matter microhalo around the PBH
Wild.