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.
List of instrument-resolved minor planets
Because of their distance from Earth and their small dimension, minor planets such as asteroids represent a challenge for astronomical instruments to resolve. Even two of the largest objects in the asteroid belt, 2 Pallas and 4 Vesta, have maximum angular diameters of less than an arcsecond. With a ground-based optical telescope, resolution of these objects through the Earth's thick atmosphere can require techniques such as speckle interferometry or adaptive optics.