Components of the HP3 heat flow probe. Top left: the radiometer (RAD), which is used to measure the radiation temperature (roughly equivalent to the ground temperature) of the surface. Right: the casing with the mole penetrometer, the temperature measuring cable (TEM-P) and the data cable (ET) connected to the lander. In addition, the casing contains an optical length meter for determining the length of the temperature measuring cable that has been pulled from the casing. The mole contains the TEM-A active thermal conductivity sensor and the STATIL tiltmeter. Bottom left: the electronic control unit, known as the back end electronics (BEE), which remains on the lander and is connected to the probe via the ET.