Seasonal Variations of Titan's Brightness

The absolute brightness of astronomical bodies can be represented by the emitted power, which plays important roles in their radiated energy budgets. The Cassini observations include three seasons of Titan, which provides an unprecedented opportunity to examine the seasonal variations of Titan's emitted power. Our analyses show that Titan's emitted power displays different seasonal behaviors between the Northern Hemisphere and the Southern Hemisphere. The global-average emitted power decreased by 6.8 +/- 0.4% during the Cassini period (2004-2017). Such a temporal variation represents the magnitude of the seasonal cycle of Titan's emitted power, which is at least one order of magnitude stronger than the seasonal variation of Earth's emitted power (<0.5%). More importantly, the similar to 6.8% decrease of the emitted power is much smaller than the similar to 18.6% decrease of the solar flux from the change of Sun-Titan distance, implying a significantly dynamical energy budget on Titan.