Microwave Imaging of Mercury's Thermal Emission: Observations and Models.

Details Microwave Imaging of Mercury's Thermal Emission: Observations and Models. Microwave Imaging of Mercury's Thermal Emission: Observations and Models.

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........59m&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, BERKELEY, 1993.Source: Dissertation Abstracts International, Volume: 54-10, Section: B

Computer Science

1

Scientific paper

We present images of Mercury's thermal emission at wavelengths of 0.3, 1.3, 2.0, 3.6, 6.2, 18.0, and 20.5 cm. In addition, images of the linearly polarized component of this emission were obtained from 2.0 to 20.5 cm. Observations were performed with the BIMA millimeter interferometer at lambda0.3 cm and with the Very Large Array at centimeter wavelengths. The thermal images are compared with a model that is based on Mariner 10 observations and lunar analogy. A re-analysis of the Mariner 10 Infrared Radiometer data shows that Mercury's regolith, like that of the Moon, consists of a thermally insulating surface layer, with a thickness of a few centimeters, atop a highly compacted region that extends to a depth of at least 4 meters. The polarization images reveal an increase in the effective dielectric constant with wavelength and rms surface slopes that range from 15^circ at lambda2.0 cm to 10 ^circ at lambda6.2 cm. These trends are caused at least in part by wavelength -dependent scattering at the surface boundary, although the density gradient near the surface may also be a contributing factor. The observed day-night brightness contrast at each wavelength requires a microwave opacity that is at least a factor of 2-3 lower than the opacity of the lunar regolith. This difference is likely due to lower Fe and Ti abundances in Mercury's regolith. Residual images obtained by subtracting the best-fit level-surface models from the data reveal thermal depressions at the poles and along the sunlit side of the morning terminator. We show that this pattern is due to shadowing by surface topography. Mercury's equatorial nightime brightness temperature spectrum from lambda3.6 cm to lambda20.5 cm shows that radiative heat transport is important within Mercury's regolith. Evidence for a turndown in the spectrum from lambda6.2 cm to lambda20.5 cm suggests that the latter wavelength begins to probe completely through the regolith and into the underlying megaregolith. This possibility does not allow us to place constraints on Mercury's lithospheric heat flow.

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