An Investigation of the Feedbacks between Pluto's Atmosphere and Surface

Grant #: NNX13AH77G
Senior Scientist: Tim Michaels

Pluto is a dynamic world. It currently possesses a significant globally-extant atmosphere that shares its composition with N2-rich volatile surface ices, and the two are assumed to be in vapor pressure equilibrium. Stellar occultations have revealed an apparent doubling in atmospheric mass since perihelion in 1989 (Elliot et al. 2003, Sicardy et al. 2003, Pasachoff et al. 2005), which is likely due to increased surface temperature driving an increase in vapor pressure – but why/how was the surface temperature still increasing more than 10 Earth-years after perihelion? Pluto's greatly elongated orbit subjects it to large seasonal variations of incoming solar energy, potentially resulting in atmospheric collapse near aphelion (next in 2112). Its icy surface exhibits an albedo field that is complex even at large scales and is known to be capable of changing quickly and markedly (Stern et al. 1997, Buie et al. 2010).

While the bulk, long-term change in global atmospheric mass can be explained using surface energy balance considerations alone (Hansen and Paige 1996), such models are not entirely consistent with the details revealed in increasingly-rich observational data sets. The full array of mechanisms producing Pluto's dynamic displays remain a mystery. However, the atmosphere may be much more than merely a passive player in the global energy and volatile mass cycles. Initial general circulation model (GCM) studies using simplified approximations of physical processes suggest strong and robust circulations in Pluto's atmosphere, including highspeed, high-altitude polar jets (Zalucha and Gulbis 2011). Therefore, the strong vapor pressure coupling between Pluto's atmosphere and surface suggests that further consideration of the atmospheric transport of energy and volatile mass beyond that assumed by Hansen and Paige (1996) has the potential to more accurately explain and resolve inconsistencies between extant volatile cycle models and observations. The work proposed herein would directly investigate the global character of Pluto's atmosphere and its two-way feedbacks with N2 ice on the surface by combining a state-of-the-art three-dimensional atmospheric model with a detailed surface/subsurface thermal model.