The Penetration of Solar Radiation Into Carbon Dioxide Ice

H E Chinnery,S R Lewis,E Kaufmann,A Hagermann

doi:10.1002/2018je005539

H E Chinnery, S R Lewis + Show 2 more

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https://doi.org/10.1002/2018je005539

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Abstract

AbstractIcy surfaces behave differently to rocky or regolith‐covered surfaces in response to irradiation. A key factor is the ability of visible light to penetrate partially into the subsurface. This results in the solid‐state greenhouse effect, as ices can be transparent or translucent to visible and shorter wavelengths, while opaque in the infrared. This can lead to significant differences in shallow subsurface temperature profiles when compared to rocky surfaces. Of particular significance for modeling the solid‐state greenhouse effect is the e‐folding scale, otherwise known as the absorption scale length, or penetration depth, of the ice. While there have been measurements for water ice and snow, pure and with mixtures, to date, there have been no such measurements published for carbon dioxide ice. After an extensive series of measurements we are able to constrain the e‐folding scale of CO2 ice for the cumulative wavelength range 300 to 1,100 nm, which is a vital parameter in heat transfer models for the Martian surface, enabling us to better understand surface‐atmosphere interactions at Mars' polar caps.

Highlights

Carbon dioxide ice is a major component of the seasonal ice caps on Mars
Based on the hypothesis of Kieffer (2000) that a largegrained slab of CO2 ice covers the Cryptic region during the southern winter and spring, Piqueux, Bryne, and Richardson (2003) were the first to define and map the distribution of the “spider” features observed in the southern polar region, confirming the correlation of spiders with the existence of highly transparent CO2 slab ice, which overlies the poorly consolidated particulate regolith of the south polar layered deposits
CO2 ice samples were prepared by condensing CO2 directly from the gas phase within a pressure vessel cooled by liquid nitrogen, following the methodology detailed in Kaufmann and Hagermann (2017)

Summary

Introduction

Carbon dioxide ice is a major component of the seasonal ice caps on Mars. Each autumn and winter, around one-third of the atmosphere condenses out to form the polar cap. Kieffer et al (2006) expanded on this, reporting that the spots and fans observed in the southern polar regions of Mars are associated with surface temperatures consistent with that of CO2 ice (~145 K) based on Mars Odyssey Thermal Emission Imaging System data, combined with anomalously low albedos These conditions persist for at least 120 sols following sunrise after the polar winter. This trapped CO2 gas eventually overcomes the cryostatic pressure, rupturing the overlying ice and causing high-velocity vents which carry particulate material along with the gas to the surface. By updating any of these parameters, of which the penetration depth (e-folding scale) of solar irradiation in CO2 slab ice is important, future models can be improved

Theory

Measurements

Results and Discussion

Conclusions