What turns some of a comet's ice into gas?

Explanation

**Step-by-Step Solution:**

1. **Understanding Comets**: Comets are celestial bodies made up of ice, dust, and rocky material. They originate from the outer regions of the solar system.

2. **Approaching the Sun**: When a comet travels towards the Sun, it enters a region of increased solar radiation and heat.

3. **Effect of Solar Radiation**: As the comet gets closer to the Sun, the intense solar radiation causes the surface temperature of the comet to rise.

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