Radar Images of the Ice Deposits at Mercury's North Pole at 70-cm Wavelength

Details Radar Images of the Ice Deposits at Mercury's North Pole at 70-cm Wavelength Radar Images of the Ice Deposits at Mercury's North Pole at 70-cm Wavelength

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.3507b&link_type=abstract

American Astronomical Society, DPS meeting #41, #35.07

Astronomy and Astrophysics

Astronomy

Scientific paper

Radar imaging of Mercury's north polar region was done using the Arecibo Observatory's 70-centimeter wavelength radar system during the inferior conjunction of July 1999. We have clearly detected the highly reflective region at Mercury's north pole first identified in radar images at the shorter wavelengths 3.6-cm and 13-cm [1,2]. The average 70-cm wavelength reflectivity of this polar region is similar to that measured at the other wavelengths over a comparable area, and the polarization ratio of 0.87 is only slightly lower. This ratio is formed from echo power returned in both circular polarizations when only one polarization is transmitted, and the observed depolarization is indicative of a multiple scattering mechanism. High resolution delay-Doppler radar maps at 3.5-cm and 13-cm wavelengths (most recently [3,4]) have demonstrated that these enhancements are located within craters near the pole, suggesting they result from ice deposits in these cold permanently shadowed depressions. Characterizing these areas is also a key goal of the current MESSENGER mission. The low absorption coefficient of ice at radio wavelengths can permit sub-surface multiple scattering mechanisms and enhance radar backscattering. Persistence of this effect over more than an order of magnitude in wavelength scale has implications for the depth and thickness of the deposits. A strong effect at the shortest wavelength implies a thin attenuating overburden. Since multiple scattering mechanisms generally require a medium many wavelengths thick, the strong effect at the long wavelength may set a minimum depth of the deposits. We acknowledge support from the NASA PG&G Program. Arecibo Observatory is part of the National Astronomy and Ionosphere Center, operated by Cornell University under cooperative agreement with the NSF.
[1] Slade et al., 1992, Science 258, 635; [2] Harmon & Slade, 1992, Science 258, 640; [3] Harmon et al., 1994, Nature 369, 213; [4] Harcke, 2005, PhD Thesis, Stanford.

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