The GP is talking about MACHOs; MAssive Compact Halo Objects. They used to be a valid DM candidate but have been ruled out 20-30 years ago. Planets don't give off any non-negligible amount of light. However, they do consist of baryons (read: atoms) which would contribute to the baryonic accoustic oscillations in the CMB power spectrum, so that's a good probe to set upper limits on baryonic matter in general.

Primordial black holes are a somewhat related candidate; but those are mostly considered ruled out as well. They are not considered baryonic matter.