Diurnal Cycles of Surface Temperature and Daily-Mean Emitted Power.

The MGS/TES observations are mainly concentrated at 2 PM and 2 AM, meaning the complete diurnal cycle of Mars’ emitted power cannot be addressed. Here, we use the temperature data from the Mars Science Laboratory Curiosity Rover (43, 44) and InSight Lander (45) to explore the diurnal cycle of surface temperature and hence emitted power for Mars. It should be mentioned that there are other in situ measurements of Mars’ surface temperature (e.g., Phoenix and Mars Exploration Rover Spirit and Opportunity), but their coverage of diurnal cycle is not as good. Therefore, these measurements are not included in our analysis of the diurnal cycle of Mars’ surface temperature.

Data obtained from Curiosity spans all four seasons, covering the first 2,500 sols on Mars, while InSight data only covers Northern spring, summer, and winter, spanning 312 sols in total. The location of the Curiosity Rover is ∼4.5°S latitude, while the InSight Lander is ∼4.5°N latitude. Both Curiosity and InSight have good diurnal coverage, so it is possible to find the 24-h average of surface temperature and hence emitted power in each season.

For processing the Curiosity and InSight data, the first step is to convert the surface temperature to the emitted power. We approximate Mars as a blackbody, so we can use the Stefan–Boltzmann equation (Eq. 2) to compute its emitted power. The main idea is to calculate the daily-mean emitted power at the surface and find the ratio between the daily-mean and 2 AM/PM average given by MGS/TES observations then use this ratio as a correction factor that is applied to the MGS/TES dataset. After calculating the emitted power at the surface based on the Stefan–Boltzmann equation (Eq. 2), we then separate the data by season. For Curiosity, all the observations used occur at evenly spaced one-hour intervals (i.e., 0, 1, 2, …, 23). To calculate the 24-h cycle for Curiosity observations, we average all data points for each individual hour point within each season. For example, we take all the 0-h points in the Northern spring season (Ls = 0 to 90°) and average them together to obtain the 0-h average for the Northern spring season. We do this for both the surface temperature and calculated emitted power. The diurnal cycle of both surface temperature and emitted power for Curiosity observations can be seen in SI Appendix, Fig. S11. For InSight, the observations are not separated by exact 1-h intervals. Therefore, in order to find the 24-h cycle, we collect all points that fall within a 1-h range for each season (i.e., 0 to 1, 1 to 2, …, 23 to 24) and then calculate the average of those points. For example, we collect all points that fall between 0 and 1 h during the Northern spring season and average them together to find the 0-h Northern spring average. This is done again for both surface temperature and calculated emitted power. The diurnal cycle of both surface temperature and emitted power for InSight observations can be seen in SI Appendix, Fig. S12.

Based on SI Appendix, Figs. S11 and S12, we can get the ratios between the daily-mean emitted power based on the complete diurnal cycle and the averaged emitted power over the two local times (2 PM and 2 AM). We take the ratios as the correction factors for the averaged emitted power based on the TES measurements at 2 PM and 2 AM (SI Appendix, Fig. S8). Using Curiosity data, we have the correction factors of 0.821, 0.841, 0.863, and 0.823 for Northern spring, summer, autumn, and winter, respectively, using Curiosity data. The correction factors for InSight are 0.850, 0.878, and 0.870 for Northern spring, summer, and winter, respectively. These correction factors are interpolated/extrapolated to all latitudes and four seasons. Then, we apply the factors to the meridional profile of Mars’ emitted power from TES measurements (SI Appendix, Fig. S8) to get the meridional profiles of the daily-mean emitted power in four seasons (Fig. 1). We also conduct the comparison of the daily-mean emitted power between MY25 autumn and the normal autumns (Fig. 2). Finally, the meridional profiles of daily-mean emitted power (Figs. 1 and ​and2)2) are averaged to global/hemispheric averages, which are shown in Fig. 3. The global/hemispheric values of Mars’ daily-mean emitted power are shown in SI Appendix, Table S2.