How did temperatures in the outer solar system affect the composition of Kuiper belt objects?

In the early solar nebula, temperatures played a critical role in determining the composition of objects based on their distance from the Sun. In the outer regions where the Kuiper belt formed, temperatures were low enough to allow volatile substances—such as water, carbon dioxide, and ammonia—to condense into ice.12

Because these volatiles were abundant in the solar nebula, the planetesimals that coalesced in these cold, outer regions became rich in ices. This contrasts with the inner solar system, where higher temperatures prevented these substances from condensing, resulting in small, rocky bodies composed primarily of silicates. Consequently, Kuiper belt objects (KBOs) are characterized as icy bodies, representing the remnants of these cold-formed planetesimals that remained unconsolidated beyond the orbit of Neptune.213