Inside a planet's core? To a degree of precision that allows us to pin any discrepancy on a poorly understood new form of matter? I can see how we can infer mas

Inside a planet's core? To a degree of precision that allows us to pin any discrepancy on a poorly understood new form of matter? I can see how we can infer mass from orbital ephemeris or gravity measurements, but understood results from both would be affected by both DM and normal matter together.