The stability of the residual carbon dioxide cap near the south pole of Mars is currently not well understood. The cap's survival depends on its radiation budget, controlled by the visible albedo and infrared emissivity. We investigated the role of CO 2 snowfall in altering the albedo and emissivity, leading to the observed asymmetry in the net CO 2 accumulation at the two poles. Uncontaminated snowfall increases albedo, and lowers emissivity, due to scattering by optically thick clouds and granular surface deposits. Data from the Mars Climate Sounder (MCS) show that fall and winter snowfall is correlated with higher springtime albedo at both poles. For the seasonal CO 2 deposits in each polar region > 60 • latitude, we find mean albedo values of 0.39 in the north and 0.51 in the south, and winter 32-μm emissivity values of 0.84 in the north and 0.87 in the south. Using a radiative transfer model and the MCS data, we find that the north polar deposits have ∼ 10× higher dust content than those in the south, explaining the ∼31% lower albedo of the north seasonal cap during spring. Our model shows that greater amounts of snowfall can explain the ∼4% lower emissivity of the north polar seasonal cap. These findings demonstrate that winter snowfall and dust transport affect the composition of Mars' seasonal ice caps and polar energy balance. Snowfall and dust loading are therefore important in modeling the CO 2 cycle on Mars, as well as the planet's long-term climate variations. Plain Language SummaryThe permanent carbon dioxide (CO 2 , also known as dry ice) deposits on Mars control the planet's global atmospheric pressure. Seasonal fluctuations of the CO 2 cycle drive pressure variations measured at the surface anywhere on the planet. These variations are buffered by the stable permanent CO 2 deposit at the south pole. The north pole has the more favorable altitude and pressure to be in equilibrium with the atmosphere, but satellite observations showed that the residual cap at the south pole was in equilibrium and not the north. Other studies found evidence of carbon dioxide snowfall in both polar regions. Using data from Mars Climate Sounder on board the Mars Reconnaissance Orbiter, we found that there is an asymmetry between the optical properties of the northern and the southern permanent caps. We attribute this asymmetry to dust and snowfall quantities, which promote more CO 2 accumulation in the south, relative to the north.
The Diviner Lunar Radiometer Experiment on board the Lunar Reconnaissance Orbiter has been mapping the temperature of the lunar surface since 5 July 2009. Past Diviner data has been used to produce global maps of nighttime temperature and to determine the thermal properties of the surface. However, the most recently published global maps only used data collected from 2009 to 2016. We recreate these global maps using all data available through July 2022: over 5 years of additional data. We implement several improvements, including a correction for errors in instrument pointing, which result in an increase in effective resolution of ∼3.5× and ∼1.3× in the longitudinal and latitudinal directions, respectively. This allows lateral brightness temperature variations to be resolved at a finer scale than was previously possible. In addition, we develop a model that mostly removes the effect of topography on nighttime temperatures. The resulting maps better highlight differences in temperature that are caused by variations in the thermal properties of the surface.
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