Mercury is much denser than Ganymede and Titan. Of course, there are thousands of smaller asteroids and comets . All of these can be seen with the naked eye or with binoculars. Object's magnitude in visible light at opposition . Do NOT look directly at the Sun.
Density is in grams per cubic centimeter.
There are also many dense asteroids, especially the M-types . The Mars meteor results notwithstanding, all of this remains very speculative . None of these prospects are really very good.