Small scale trench in the Martian soil: Conditions for condensation of atmospheric volatiles

This paper analyzes the diurnal evolution of temperature inside and in the vicinity of a small scale trench in the martian soil. Although the work pre sented was motivated by the artificial trench to be dug during the Mars Pol ar Lander (MPL) mission, the results are also applicable to natural structu res, The models are calculated for conditions of region close to the south pole, matching those of the landing site for the MPL. Two trench geometries are considered. One has a rectangular cross section which could be achieve d under the ideal condition of no material falling back during digging and the other has a trapezoidal cross section with the side walls inclined at 4 5 degrees. Both trenches have flat bottoms and are assumed to be long enoug h to allow a 2D treatment of the heat conduction in the soil. In the case o f a rectangular trench it is found that the water frost accumulation is exp ected on a significant part of the inner surfaces of the trench irrespectiv e of the season. Some condensation of carbon dioxide could also proceed if the thermal diffusivity of the soil is close to the lowest available estima tes. Frost formation in a trench with inclined walls is also possible depen ding on the assumed value of thermal diffusivity. The amount of frost shoul d be large enough to allow the imaging of its accumulation with the Robotic Arm Cam era of the Mars Volatile and Climate Surveyor experiment payload o n the MPL. (C) 2000 Academic Press.