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Why does Mercury have such extreme temperature changes?
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Mercury
Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.
Mercury experiences extreme temperature fluctuations primarily because it lacks a significant atmosphere to trap heat or distribute it across the planet's surface.1
Because the planet is so small and hot, it cannot retain a substantial gaseous envelope; its surface pressure is less than one-trillionth that of Earth. Without an insulating atmosphere, heat absorbed during the long days is rapidly lost to space during the long nights.123
These temperature extremes are further influenced by Mercury's unique orbital and rotational characteristics:
- Slow Rotation: Mercury’s solar day lasts 176 Earth days, meaning the surface is exposed to intense sunlight for an extended period, followed by an equally long, frigid night.3
- Orbital Eccentricity: Mercury has a highly elongated orbit, which causes the intensity of solar radiation to vary significantly as the planet moves between perihelion and aphelion.3
Consequently, surface temperatures can soar above 700 K (800 °F) at the equator during the day and plummet to about 90 K (−300 °F) before sunrise.23