  The NASA InSight Lander on Mars includes the Heat Flow and Physical
Properties Package HP$^3$ to measure the surface heat flow of the planet. The
package uses temperature sensors that would have been brought to the target
depth of 3--5 m by a small penetrator, nicknamed the mole. The mole requiring
friction on its hull to balance remaining recoil from its hammer mechanism did
not penetrate to the targeted depth. Instead, by precessing about a point
midway along its hull, it carved a 7 cm deep and 5-6 cm wide pit and reached a
depth of initially 31 cm. The root cause of the failure - as was determined
through an extensive, almost two years long campaign - was a lack of friction
in an unexpectedly thick cohesive duricrust. During the campaign -- described
in detail in this paper -- the mole penetrated further aided by friction
applied using the scoop at the end of the robotic Instrument Deployment Arm and
by direct support by the latter. The mole finally reached a depth of 40 cm,
bringing the mole body 1--2 cm below the surface. The penetration record of the
mole and its thermal sensors were used to measure thermal and mechanical soil
parameters such as the thermal conductivity and the penetration resistance of
the duricrust and its cohesion. The hammerings of the mole were recorded by the
seismometer SEIS and the signals could be used to derive a P-wave velocity and
a S-wave velocity and elastic moduli representative of the topmost tens of cm
of the regolith. The combined data were used to derive a model of the regolith
that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated
layer of sand mixed with dust and above another 10 cm of unconsolidated sand.
Underneath the latter, a layer more resistant to penetration and possibly
consisting of debris from a small impact crater is inferred.
