The Heat Flow and Physical Properties Package HP3 on InSight: Status and First Results

Abstract

The Heat Flow and Physical Properties Package HP3 in March 2019 started to deploy a self-burrowing probe to a depth of up to 5m, deep enough to reach beyond the temperature waves from diurnal and annual perturbations. The probe - nicknamed the mole - carries a tether to depth equipped with temperature sensors to measure the temperature gradient and houses a set of self-heated sensors to measure the thermal conductivity at depth at 50 cm intervals. It further includes a tiltmeter to measure the attitude upon penetration and a device to measure the length of tether buried. From the temperature gradient and the thermal conductivity, the planetary heat flow will be calculated. In addition, the package includes a radiometer, the results of which are presented in Müller et al. (2019) at this meeting. Unfortunately, the mole got stuck at a depth of 35cm. Interpretation of the available penetration data suggests that the mole punched through a duricrust of perhaps about 10cm thickness that provided significant initial resistance to the penetration. While the mole penetrated further to 35cm depth using the weight of its support structure to balance recoil, the duricrust and the regolith underneath failed to provide the necessary friction once the mole had left the support structure. By the time of the fall meeting, InSight will have attempted to use its robotic arm to break the duricrust, compact the porous regolith and load it to provide sufficient friction for further penetration, hopefully to the target depth. The pit that the mole has carved is twice as wide as the diameter of the mole. Together with the inclination of 20° of the mole axis with respect to gravity this suggests precession of the mole and/or lateral movement. Images of the pit further suggest that the duricrust fails upon being stressed and compacts significantly thus indicating a substantial porosity of the latter.