Answer :
Final answer:
Space vehicles heat up upon re-entry due to the high temperatures in the thermosphere, despite the thinness of the atmosphere.
Explanation:
Space vehicles heat up as they enter the atmosphere despite its thinness because the upper atmosphere, specifically the thermosphere, absorbs high energy ultraviolet and x-ray radiation from the sun, causing the temperature to increase significantly. This results in space vehicles heating up due to the high temperatures encountered during re-entry.
Additionally, even though the overall atmosphere is thin, the thermosphere's temperature can reach as high as 2,000°C, which contributes to the heating of space vehicles traveling through it. The low density of air at this level means the heat content is low, but the absorbed energy is enough to cause a significant temperature rise in objects entering this layer.
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