What causes a comet's tail to form?

• A. Dust released from the comet as it heats near the Sun
• B. The tail forms when the comet collides with a planet
• C. Dust and gas are pushed away from the Sun by radiation pressure and solar wind as the comet approaches the Sun
• D. The tail forms only after the comet leaves the solar system

Answer: (C)

When a comet gets close to the Sun, heat causes ices on its nucleus to sublimate, releasing gas and dust. The Sun’s radiation pressure pushes dust grains away, while the solar wind—a flow of charged particles—drags ionized gas outward, creating an ion tail. Together, these solar forces drive material away from the Sun, forming the two tails that always point away from the Sun as the comet approaches. This description matches the idea that both dust and gas are propelled by solar radiation and solar wind, not by collisions or by the comet leaving the solar system.