Dimming titan revealed by the Cassini observations.

Liming Li

doi:10.1038/srep08239

Abstract

Here we report the temporal variation of Titan's emitted energy with the Cassini/CIRS observations. In the northern hemisphere, the hemispheric-average emitted power decreased from 2007 to 2009 and increased from 2009 to 2012–13, which make the net change insignificant (0.1 ± 0.2%) during the period 2007–2013. The decrease from 2007 to 2009 is mainly due to the cooling around the stratospause, and the increase from 2009 to 2012–13 is probably related to temporal variation of atmospheric temperature around the tropopuase in the northern hemisphere. In the southern hemisphere, the emitted power continuously decreased by 5.0 ± 0.6% from 2.40 ± 0.01 W/m2 in 2007 to 2.28 ± 0.01 in 2012–13, which is mainly related to Titan's seasonal variation. The asymmetry in the temporal variation between the two hemispheres results in the global-average emitted power decreasing by 2.5 ± 0.6% from 2.41 ± 0.01 W/m2 in 2007 to 2.35 ± 0.01 W/m2 in 2012–13. The solar constant at Titan decreased by ~13.0% in the same period 2007–2013, which is much stronger than the temporal variation of emitted power. The measurements of Titan's absorbed solar power are needed to determine the temporal variation of the global energy budget.

Highlights

We report the temporal variation of Titan’s emitted energy with the Cassini/Composite Infrared Spectrometer (CIRS) observations
The meridional profiles of emitted power suggest that the temporal variation of emitted power behaves differently at different latitudes
The seasonal change of emitted power is different between the two hemispheres during the period of 2007–2013

Summary

Liming Li

We report the temporal variation of Titan’s emitted energy with the Cassini/CIRS observations. The measurements of Titan’s absorbed solar power are needed to determine the temporal variation of the global energy budget. For a basically equilibrium climate like the current one on our home-planet Earth, the two energy components (i.e., the emitted thermal energy and the absorbed solar energy) are roughly balanced[1,2], even though there are small fluctuations[3,4,5,6] with a magnitude of ,0.1% in the global-average energy components. The Cassini/CIRS observations have already been used to examine the global emitted thermal energies of some astronomical bodies[10,11,12]. We explore the temporal variation of Titan’s emitted power, which is one component of its global energy budget, with the long-term Cassini/CIRS observations.

Results

Observational Time

Discussion

Additional information