Ten-Micron Eclipse Observations of Io, Europa, and Ganymede

Eclipse observations of Jupiter's satellites Io, Europa, and Ganymede have been obtained in an 8 to 14-μm band pass during 1971. The simplest thermal model able to explain the data for each satellite is a two-layer surface structure with an upper layer, only a few millimeters thick, having low thermal conductivity consistent with fine rock powder or frost, and a subsurface having high thermal conductivity consistent with solid rock or dense ice. The upper layer on Io (γ = 1100 ± 100) ² appears to be different from that on Europa (γ = 3000 ± 1000) and Ganymede (γ = 3400 ± 700), but the two-layer model fits all three satellites.