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.