Hottest planets in the solar system
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Hottest Planets in the Solar System: Key Temperature Insights
Mercury and Venus: The Solar System’s Hottest Planets
In our solar system, Venus is the hottest planet, not Mercury, despite Mercury being closer to the Sun. Venus’s thick atmosphere, rich in carbon dioxide, traps heat through a runaway greenhouse effect, resulting in surface temperatures that can exceed 460°C (860°F) . Mercury, while extremely hot on its sunlit side, lacks a substantial atmosphere to retain heat, so its surface temperatures can swing dramatically between day and night.
Exoplanet Comparisons: Hot Jupiters and Ultra-Hot Jupiters
When comparing to planets outside our solar system, so-called "hot Jupiters" and "ultra-hot Jupiters" are among the hottest known planets. These are gas giants that orbit very close to their stars, leading to dayside temperatures often exceeding 1,700 K (about 1,430°C or 2,600°F) Deming2023Baxter2020. Some of the hottest exoplanets, like WASP-18b and Kepler-13Ab, have dayside temperatures measured at over 3,000 K (about 2,700°C or 4,900°F) Shporer2014Nymeyer2010. KELT-9b, the hottest known exoplanet, has a dayside temperature above 4,500 K (about 4,200°C or 7,600°F), hotter than some stars Lothringer2018Jones2022.
Temperature Transitions and Atmospheric Effects
Research shows a clear transition in atmospheric properties for hot Jupiters at around 1,660–1,800 K. Above this threshold, planets often develop temperature inversions in their atmospheres, where the temperature increases with altitude due to the absorption of stellar radiation by atomic metals and other species Deming2023Lothringer2018Baxter2020. These inversions make the hottest planets even more efficient at trapping and emitting heat.
Notable Hot Exoplanets
- KELT-9b: The hottest known exoplanet, with a dayside temperature over 4,500 K Lothringer2018Jones2022.
- WASP-18b: Dayside temperatures around 3,100–3,300 K, with almost no heat redistribution to the night side .
- Kepler-13Ab: Dayside temperature of about 2,750 K, with evidence of a temperature inversion .
- HD 149026b: Brightness temperature measured at 2,300 K, challenging previous models of planetary heat emission .
Ultra-Short-Period Terrestrial Planets
Some rocky exoplanets with very short orbital periods also reach extreme temperatures. For example, TOI-2260 b, a terrestrial planet candidate, is estimated to have an equilibrium temperature of about 2,600 K .
Conclusion
Within our solar system, Venus is the hottest planet due to its thick, heat-trapping atmosphere. However, many exoplanets, especially hot Jupiters and ultra-hot Jupiters, reach much higher temperatures, with KELT-9b being the hottest known planet overall. These extreme temperatures are driven by close proximity to their stars and unique atmospheric processes, including temperature inversions and efficient heat trapping by atomic and molecular species Deming2023Lothringer2018Shporer2014+3 MORE.
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