An analysis of the stability and transport of carbon dioxide on Mars and Iapetus: Increasing accuracy via experiments and photometry.

摘要

Volatile transport of carbon dioxide is most relevant on two planetary bodies in our solar system: Mars and Iapetus. We experimentally measured the sublimation rate of CO2 ice under simulated martian conditions and developed a model based on our experimental results. We experimentally verified that solar irradiance is the primary control for the sublimation of CO2 ice on the martian poles with the amount of radiation striking the surface being controlled by variations in the optical depth, ensuring the formation and sublimation of the seasonal cap. Our model, supported by comparison of MGS-MOC and MRO-HiRISE images, shows that ∼ 0.4 m is currently being lost from the south perennial cap per martian year. In order to build a similar model for Iapetus, one key parameter was needed: the bolometric Bond albedo. We used photometry of Cassini VIMS observations of Iapetus to produce the first phase integrals calculated directly from solar phase curves of Iapetus for the leading hemisphere and to estimate the phase integrals for the trailing hemisphere. Our phase integrals, which are lower than previous results, have profound implications for the analyses of the energy balance and volatile transport on this icy satellite. We also utilized Cassini VIMS and ISS and Voyager ISS observations of Iapetus to produce the first bolometric Bond albedo map of Iapetus; the average albedo values for the leading and trailing hemispheres are 0.25 +/- 0.03 and 0.05 +/- 0.01 respectively. On Iapetus, which has no detectable atmosphere, any carbon dioxide sublimating from the dark material, where it was discovered by reflectance spectroscopy, would either escape the body or migrate on ballistic trajectories to a possible polar cold trap. However, through proof by contradiction, we show that if dry ice is the source of the detected signal in the dark material, it produces an impossible scenario where an extensive polar cap is produced along with incorrect temperatures for the dark material at equatorial latitudes. After ruling out surface dry ice as the source, we set upper limits on the amount of CO2 transport that can occur on Iapetus without forming a polar cap.