A Comparative Investigation of Exobase Temperatures at Venus, Earth, Mars, and Titan: Role of Solar Forcing

Abstract Understanding the mechanisms controlling exobase temperature is essential for constraining planetary atmospheric escape and long‐term climate evolution. While this has been extensively studied on individual bodies, comparative analyses across multiple bodies remain limited. Here, we compare exobase temperatures on Venus, Earth, Mars, and Titan, all showing a clear positive correlation with integrated solar extreme ultraviolet flux, thus identifying solar heating as the primary driver. Notably, the observed temperature responses exhibit trends that are consistent with theoretical expectations for all three inner planets. For Titan, although a clear response trend to solar EUV forcing remains evident, the absolute magnitude deviates substantially from the theoretical estimate. This supports a common energy balance between solar heating and thermal conduction in the upper atmosphere across a variety of solar system bodies that differ greatly in heliocentric distance, local gravity, and dominant atmospheric composition. Deviations from this general trend suggest additional energy sources, including geomagnetic heating on Earth, dust‐induced solar absorption on Mars, and magnetospheric plasma precipitation on Titan.