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What causes a Kuiper belt object to develop a coma and tail after moving closer to the Sun?

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Kuiper belt binary object — Kuiper belt An artist's rendition of a binary object in the Kuiper belt. The two objects depicted orbit each other at the edge of the solar system.

When a Kuiper belt object moves closer to the Sun, it may develop a coma and tail due to the sublimation of its volatile ices.1

Kuiper belt objects are composed largely of volatile ices—such as water, carbon dioxide, and ammonia—mixed with dust particles. While these objects remain inactive in the cold, distant reaches of the Kuiper belt, their approach to the Sun exposes them to increased solar radiation. This heat causes the ices to sublimate, transitioning directly from solid to gas.123

As these gases evolve from the nucleus, they expand into the vacuum of space, carrying fine dust particles with them to form a bright, outflowing atmosphere known as a coma. Subsequently, solar radiation pressure and the solar wind act upon the gas and dust, pushing them away from the Sun to create the characteristic cometary tail.214