The thermal and electrical conductivity probe (TECP), a component of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA), was included on the Phoenix Lander to conduct in situ measurements of the exchange of heat and water in the Martian polar terrain. TECP measured regolith thermal conductivity, heat capacity, temperature, electrical conductivity, and dielectric permittivity throughout the mission. A relative humidity sensor returned the first in situ humidity measurements from the Martian surface. The dry overburden above the ground ice is a good thermal insulator (average κ = 0.085 W m−1 K−1 and average Cρ = 1.05 × 106 J m−3 K−1). Surface thermal inertia (I) calculated from these values agrees well with daytime orbital determinations, but differences in the spatial and temporal scale of heat transport lead to very different measurements at night. Electrical conductivity was consistent with open circuit throughout the mission; an upper limit conductivity of 2 nS cm−1 is derived. Bulk dielectric permittivity (ɛb) shows several puzzling signals but also a systematic increase overnight in the latter half of the mission, contemporaneous with H2O adsorption. The magnitude of the increase is difficult to reconcile with expected changes in unfrozen water. Atmospheric H2O averages around 1.8 Pa during the day, corresponding to a RH < 5%. At night, much of the H2O disappears from the atmosphere, and RH increases to ∼100%. Temperature and H2O partial pressure data suggest that adsorption on mineral surfaces plays a major role in scrubbing H2O, with a possible contribution from perchlorate salts.

Thermochron iButtons incorporate the latest in digital technology, making them smaller, less expensive, durable and potentially more reliable than many other temperature logging devices. The objective of this study was to test the accuracy of an inexpensive air temperature measurement system, composed of a Thermochron iButton and radiation shield. Sixty-one iButtons were subjected to a sequence of two water baths (0°C and 24·9°C) to assess the absolute accuracy of the sensors. Five solar radiation shields were tested in a greenhouse setting to evaluate the reduction in radiative heating. Significant differences (p < 0·05) were detected between instruments subsequent to both water-bath treatment analyses. The accuracy of the sensors was well within the manufacturer's stated specification of ±1·0°C with a collective temperature variance of ±0·21°C. Temperature responses generated by the Thermochron iButtons in different radiation shields were consistent, but varied significantly (p < 0·05) from 28 to 44°C based on diurnal temperature ranges. Results indicate that the Thermochron iButton is an accurate, inexpensive alternative to more expensive temperature datalogging systems, and is well suited for obtaining quality spatially distributed data for hydrologic and water quality investigations.

[1] The Thermal and Electrical Conductivity Probe (TECP) is a component of the Microscopy, Electrochemistry and Conductivity Analyzer (MECA) payload on the Phoenix Lander. TECP will measure the temperature, thermal conductivity, and volumetric heat capacity of the regolith. It will also detect and quantify the population of mobile H 2 O molecules in the regolith, if any, throughout the polar summer, by measuring the electrical conductivity of the regolith as well as the dielectric permittivity. In the vapor phase, TECP is capable of measuring the atmospheric H 2 O vapor abundance as well as augmenting the wind velocity measurements from the meteorology instrumentation. TECP is mounted near the end of the 2.3 m Robotic Arm and can be placed either in the regolith material or held aloft in the atmosphere. This paper describes the development and calibration of the TECP. In addition, substantial characterization of the instrument has been conducted to identify behavioral characteristics that might affect landed surface operations. The greatest potential issue identified in characterization tests is the extraordinary sensitivity of the TECP to placement. Small gaps alter the contact between the TECP and regolith, complicating data interpretation. Testing with the Phoenix Robotic Arm identified mitigation techniques that will be implemented during flight. A flight model of the instrument was also field tested in the Antarctic Dry Valleys during the