Asteroid
Although their location in the asteroid belt excludes them from planet status, the three largest objects, Ceres, Vesta, and Pallas, are intact protoplanets that share many characteristics common to planets, and are atypical compared to the majority of "potato"-shaped asteroids. The fourth largest asteroid, Hygiea, has an undifferentiated interior, like the majority of asteroids. Between them, the four largest asteroids constitute half the mass of the asteroid belt.
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.