A sensor to perform in-situ thermal conductivity determination of cometary and asteroid material

Measurements of the physical properties of surface and subsurface layers of planetary bodies often provide important information about the structure of the medium and processes that occur there. Thermal properties of the subsurface material of cometary nuclei are crucial in determining the heat and gas transport. Similarly, asteroids’ regolith is a buffering zone for the process of heat transfer from the surface to the interior of a body and vice versa. There are space experiments planned to perform temperature and thermal conductivity measurements on a comet (ROSETTA) and one can easily foresee such measurements carried out by future robotic missions on Mars, planetary satellites and asteroids. In this paper we present the results of measurements carried out with a new type of thermal sensors. The elementary cylindrical sensor is made of platinum wire (resistance thermometer) and isotan wire (heating element) that can operate independently. Their advantage is that they use very well known and calibrated materials for temperature sensors (platinum) and for heaters (isotan). By choosing these materials the problems of temperature measurement, calibration and constant heating power are resolved. We interpret the results of measurements made for a number of sensors combined into a long cylinder in teflon, delrin, ice-dust mixture (comet analogue) and regolith-like material in terms of numerical models and show that the obtained values of thermal conductivity are in agreement with what one could expect. Therefore, we can recommend both the sensors and the method of data interpretation for the thermal conductivity determination as very useful tools for future space missions and in laboratory experiments on cometary and asteroid material analogues.