Asteroid
The dwarf planet Ceres is by far the largest asteroid, with a diameter of . The next largest are 4 Vesta and 2 Pallas, both with diameters of just over . Vesta is the only main-belt asteroid that can, on occasion, be visible to the naked eye. On some rare occasions, a near-Earth asteroid may briefly become visible without technical aid; see 99942 Apophis.
1299 Mertona
According to the surveys carried out by the Japanese Akari satellite and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, "Mertona" measures between 14.14 and 14.60 kilometers in diameter, and its surface has an albedo between 0.219 and 0.243. Although such a high albedo is typical for stony asteroids, the "Collaborative Asteroid Lightcurve Link" assumes an albedo of 0.057, which it uses as the generic albedo for all carbonaceous C-type asteroids. It therefore calculates a larger diameter of 27.90 kilometers (as the lower the albedo or reflectivity, the larger a body's diameter at an unchanged absolute magnitude or brightness). Carbonaceous asteroids are the predominant type in the outer main-belt, while stony asteroids are mostly found in the inner regions of the asteroid belt.