I'm not good at physics, but it seems to me if this 9mm object had the mass of earth, then at a distance of about 6400 km it would exert 1G, and at minimal distance, it would exert about a zillion Gs. So even assuming it didn't pull in matter per se, the gravity and tidal forces ought to destroy earth about as effectively as colliding with a regular earth sized planet.

No it wouldn't, but I'm thinking it would be able to transfer some kinetic energy to the earth which would be a very very bad thing.