CO2 Snow on Mars and Early Earth: Experimental Constraints
✍ Scribed by David L. Glandorf; Anthony Colaprete; Margaret A. Tolbert; Owen B. Toon
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 234 KB
- Volume
- 160
- Category
- Article
- ISSN
- 0019-1035
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✦ Synopsis
Greenhouse warming due to carbon dioxide atmospheres may be responsible for maintaining the early Earth's surface temperature above freezing and may even have allowed for liquid water on early Mars. However, the high levels of CO 2 required for such warming should have also resulted in the formation of CO 2 clouds. These clouds, depending on their particle size, could lead to either warming or cooling. The particle size in turn is determined by the nucleation and growth conditions. Here we present laboratory studies of the nucleation and growth of carbon dioxide on water ice under martian atmospheric conditions. We find that a critical saturation, S = 1.34, is required for nucleation, corresponding to a contact parameter between solid water and solid carbon dioxide of m = 0.95. We also find that after nucleation occurs, growth of CO 2 is very rapid, and we report the growth rates at a number of supersaturations. Because growth would be expected to continue until the CO 2 pressure is lowered to its vapor pressure, we expect particles larger than those being currently suggested for the present and past martian atmospheres. Using this information in a microphysical model described in a companion paper, we find that CO 2 clouds are best described as "snow," having a relatively small number of large particles.