Final answer:
Objects in the asteroid belt consist largely of fragments of planetesimals or undifferentiated bodies from the early solar system. While some asteroids are differentiated, most retain their original composition, serving as chemical fossils that shed light on the formation of the solar system. They are not actively accreting material and growing, nor are they unbroken planetesimals.
Step-by-step explanation:
The objects located in the asteroid belt are indeed remnants of fragmented planetesimals. The asteroid belt, which lies between Mars and Jupiter, is a region where these remnants can exist in stable orbits, escaping impacts with the planets or ejection from the solar system. Most of the bodies in this region are either undifferentiated or are fragments of differentiated bodies. The largest bodies in the belt, such as Vesta, may have differentiated interiors, but many asteroids are unmodified material dating back to the formation of the solar system and represent the original composition of the solar nebula.
Some planetesimals were able to grow by accreting smaller bodies through a process called accretion, eventually becoming protoplanets. However, not all objects in the asteroid belt are actively accreting and growing more massive today; most are stable in their current form. Furthermore, many asteroids in the belt are rubble piles or aggregates of smaller pieces, suggesting they are not unbroken planetesimals. Thus, these asteroids are like chemical fossils, providing scientists with a glimpse into the early solar system.