# Explain why a planet with a thin atmosphere has a much greater diurnal (day–night) temperature variation than a planet with a thick atmosphere containing greenhouse gases.

> IB DP Physics Higher Level (2023 syllabus) — B.2 Greenhouse effect · Explain · 4 marks

> Astronomers compare the surface temperatures of two similarly sized rocky planets orbiting the same star at the same distance. Planet A has a thick atmosphere rich in greenhouse gases; Planet B has a very thin atmosphere with negligible greenhouse gas concentration.

## Mark scheme (4 marks)

1. The surface of Planet B absorbs shortwave radiation from the star during the day, causing its temperature to rise, but with no significant atmosphere it cannot retain this energy at night.
2. Greenhouse gases in Planet A's atmosphere absorb outgoing longwave (infrared) radiation emitted by the surface.
3. The atmosphere of Planet A re-emits this infrared radiation in all directions, including back towards the surface, keeping the surface warmer at night.
4. Planet A's atmosphere therefore acts as a thermal buffer, reducing both the daytime maximum and raising the night-time minimum, so the overall diurnal range is much smaller than for Planet B.

## Key terms

- [greenhouse gas](https://www.gradenine.co.uk/glossary/greenhouse-gas)

## Related

- [Revision notes for IB DP Physics Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-planet-with-a-cdb0a90e) · Published by Druglandscape Ltd.