Mercury: Epilith Physical Parameters and a Hermocentric Longitude Dependence of its 3.3‐mm Radiation

Abstract

Observations of Mercury at 3.3 mm were made on 35 days in 1967 and 82 days in 1968 to (1) search for a dependence of the disk‐average brightness temperature T B on hermocentric longitude and (2) to provide constraints on the range of values of the thermal parameters of the epilith (subsurface layers) of Mercury. The observations can be represented by urn:x-wiley:00486604:media:rds223:rds223-math-0001 where the statistical standard errors are indicated, ϕ is the phase angle, and l′ is the hermocentric longitude of the subearth point. The estimated over‐all system calibration error is 10%. The longitude dependence is demonstrated more clearly when individual phase variation curves are plotted for separate longitude intervals. The ratio of electrical to thermal skin depths (normalized by the wavelength) δ/λ (cm −1 ) is 1.3 (+ 1.4, ‐ 0.8); the error estimate is very conservative. The observations have been compared with the series of models by Morrison [1969]; of these models, the one with δ/λ = 1.37 and a conductivity independent of temperature best represents the data.