JPL fits for 2016 NJ33 and 2013 XY20 require sphere density times diameter below 4100 kg/m² if sunlight supplies the force

We tested whether sunlight can supply the extra forces beyond gravity in eight archived JPL fits for dark comets. A photon momentum bound gives a minimum illuminated area per unit mass. We used the full covariance of the three force terms. We formed nominal joint 95% limits under a Gaussian fit model. For spheres, the density times diameter must be at most 4051 kg/m² for 2016 NJ33 and 3788 kg/m² for 2013 XY20. With albedo from 0.04 to 0.60 and catalog absolute magnitude shifted by up to 0.3 magnitudes, both density limits are below 350 kg/m³. The bound allows any direction for reflected light and thermal radiation. It requires passive energy balance and the released constant inverse-square force model. It does not measure density or identify gas loss. Model error, data bias, and fit selection are outside the formal coverage. The package contains 14 native JPL records, source hashes, code, numerical witnesses, figures, and offline reproduction instructions.

dark comets · nongravitational acceleration · solar radiation pressure · photon momentum · orbit covariance · small bodies · reproducible research