Initial results from the thermal and electrical conductivity probe (TECP) on Phoenix

Abstract

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 × 10 6 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 (ɛ b ) shows several puzzling signals but also a systematic increase overnight in the latter half of the mission, contemporaneous with H 2 O adsorption. The magnitude of the increase is difficult to reconcile with expected changes in unfrozen water. Atmospheric H 2 O averages around 1.8 Pa during the day, corresponding to a R H < 5%. At night, much of the H 2 O disappears from the atmosphere, and R H increases to ∼100%. Temperature and H 2 O partial pressure data suggest that adsorption on mineral surfaces plays a major role in scrubbing H 2 O, with a possible contribution from perchlorate salts.