The total mass and distribution of dark matter within the Solar system are poorly known, albeit constraints from measurements of planetary orbits exist. We have discovered, however, that different sorts of determinations of the Sun’s gravitational quadrupole moment can combine to yield new and highly sensitive constraints on the mass distribution within Mercury’s orbit. The best determinations point with high confidence to the existence of a non-luminous disk coplanar with Mercury’s orbit, and the mass estimates associated with known matter, although uncertain, point to a significant dark-matter contribution, for which macroscopic dark matter or macroscopic constructs of ultralight dark matter may suit best. I will review the possibilities and consider how our constraints may be refined still further and our suppositions tested.
