Mars: VLA observations of the Northern Hemisphere and the north polar region at wavelengths of 2 and 6 cm

Donald J. Rudy, Duane O. Muhleman, Glenn L. Berge, Bruce M. Jakosky, Philip Christensen

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Abstract

Observations of Mars at wavelengths of 2 and 6 cm were made using the VLA in its A configuration. The season on Mars was late spring in the Northern Hemisphere (Ls = 60°). The sub-Earth latitude was 25°N, so the geometry for viewing the north polar region was optimal. Whole-disk brightness temperatures were estimated to be 193.2 ± 1.0°K at 2 cm and 191.2 ± 0.6°K at 6 cm (formal errors only). Since measurements of the polarized flux were taken at the same time, whole-disk effective dielectric constants could be estimated and from these estimates of subsurface densities could be made. The results of these calculations yielded a whole-disk effective dielectric constant of 2.34 ± 0.05, which implied a subsurface density of 1.24 ± 0.11 g cm-3 at 2 cm. The same calculations at 6 cm yielded an effective density of 1.45 ± 0.10 g cm-3 and dielectric constant of 2.70 ± 0.10. From the mapped data these parameters were also estimated as a function of latitude between latitudes of 15°S and 60°N. In addition to the effective dielectric constant and subsurface density, the radio absorption length of the subsurface was estimated. The radio absorption length for most of these latitudes was about 15 wavelengths with formal errors on the order of 5 or 10 wavelengths. The estimation of the effective dielectric constant at most latitudes was between 2 and 3.5 with only slight differences between the two different wavelengths. These estimates of the dielectric constant lead to estimation of the subsurface densities as a function of latitude. Most calculations of the subsurface density yielded results between 1 and 2 g cm-3 with errors on the order of 0.5 g cm-3. These results seem to imply that the subsurface is not much different than the surface as observed by the Viking and Mariner missions. In line with this, a comparison of the correlation of the dielectric constant at each wavelength with the thermal inertia determined from infrared measurements of the surface temperature shows that the correlation at 2 cm is slightly stronger than the correlation at 6 cm. Since the 2-cm radiation comes from a region closer to the surface than the 6-cm radiation, this decrease in correlation with depth is consistent with the idea that the physical makeup of the subsurface is varying slowly in the near subsurface region.

Original languageEnglish (US)
Pages (from-to)159-177
Number of pages19
JournalIcarus
Volume71
Issue number1
DOIs
StatePublished - Jul 1987

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ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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