Thermal radiation from the Galilean satellites measured at 10 and 20 microns

[摘要] The four Galilean Satellites have been observed in two broad bandpasses, centered near 10μ and 20μ respectively, during Jupiter's 1971-apparition.Two types of measurements were obtained. The first consisted of monitoring the infrared flux as a function of each satellite's orbital position, the other of flux measurements during satellite eclipses. The latter type was obtained only in the 10μ bandpass, and only for lo (J1), Europa (J2), and Ganymede (J3), because Callisto (J4) was not eclipsed in 1971.The flux measurements obtained as a function of orbital position were averaged for each satellite and bandpass, and from the mean values the following quantities were derived: (1) the maximum (~subsolar) surface temperature, T_(max), (2) the ratio between the effective 20μ emissivity, ε_(20), and the effective 10μ, emissivity, ε_(10), (3) the bolometric Bond albedo, A_(bol), and (4) the effective phase integral, q. The results, listed in Table (i), indicate very low "ε_(20)/ε_(10) " ratios and high q-values.The 10μ flux measurements obtained during eclipses of J1, J2, and J3 have been compared to thermal models, and the following conclusions were drawn. (1) No homogeneous model [single parameter, y = (kpc)^(-1/2) can account for the observed temperature variations during eclipses. (2) A two- layer model with a thin, thermally insulating layer covering a highly conductive subsurface is adequate to explain all the observations. (3) The atmospheric surface pressure on J1, J2, and J3 is less than 1 mbar. (4) The results, listed in Table (ii), show that the surface covering of J1 is distinctly different from that of J2 or J3.

[发布机构] University:California Institute of Technology;Department:Geological and Planetary Sciences

[关键词] Geology