Structure of the Martian soil directly below the InSight landing site
Structure of the Martian soil directly below the InSight landing site
Temperature measurements in the uppermost Martian soil were taken using DLR's HP³ experiment at the In-Sight landing site and collected over many Martian days and thus across seasonal changes. They provided new insights into the formation and structure (left) of Mars's 'duricrust soil'. The temperatures are high enough for brines (salty liquids) to form when the humidity of the atmosphere in the Martian winter and spring allows it. Thermal conductivity measurements using the HP³ probe have shown that the soil 'breathes' over the seasons. As humidity decreases, the brine crystallises and the salts encrust the Martian soil. This happens at the landing site down to a depth of around 20 centimetres, providing an explanation as to why the InSight 'mole' was unable to penetrate deeper into the Martian soil. When penetrating the duricrust, the mole created a hole as it hammered and therefore failed to generate enough friction in the upper 20 centimetres. The duricrust soil is covered by one to two centimetres of Martian dust and sand, with a layer of volcanic sand and debris below. On the right, the filled pit, traces from the lander's gripper arm can be seen, and the pressure point where the arm was used to compact the soil to enable deeper penetration through higher friction.
Credit:
GRL (T. Spohn et al.); NASA/JPL-Caltech