HR: 1340h
AN: P13A-0974    [Abstracts]
TI: Martian residual-ice cap albedos from MOLA radiometry
AU: * Byrne, S
EM: shane@quake.mit.edu
AF: MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Zuber, M T
EM: zuber@tharsis.gsfc.nasa.gov
AF: MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Neumann, G
EM: neumann@tharsis.gsfc.nasa.gov
AF: MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: The retreat of the Martian seasonal CO$_2$ ice caps uncovers bright residual ice caps that persist throughout the rest of the year and partially cover the underlying polar layered deposits. On the north polar layered deposits this residual ice is composed of dirty H$_2$O ice [Kieffer et al., Science, 1976]. Its thickness is unknown; however, it is thin enough to vary in lateral extent from year to year [Malin and Edgett, JGR, 2001]. On the south polar layered deposits this residual ice is composed of high-albedo solid CO$_2$ [Kieffer, JGR, 1979]. It is on the order of a few meters thick [Byrne and Ingersoll, Science, 2003]. MOLA has been operating as a high resolution (both spectrally and spatially) radiometer since the end of altimetry operations in mid-2001. The convergence of orbital tracks at the poles means that complete albedo maps of both residual caps can be generated with MOLA radiometry data spanning a short range of season and with little or no interpolation. The high resolution nature of these data presents an opportunity to attempt new measurements and revisit old problems. The albedo of the southern residual cap has been observed to increase during the summer season in response to increased insolation [Paige, Caltech thesis 1985; James et al., Mars book, 1992, Kieffer et al., JGR, 2000]. The reasons behind this phenomenon are unclear but may be related to heating of surface dust grains which can then sublimate ice beneath them allowing the grains to burrow into the ice or microphysical changes in the ice in response to the increased incident energy. Initial examination of MOLA radiometry indicates the same effect can be observed with this dataset. The high spatial resolution of these data will resolve which areas of the southern residual cap are responsible for this brightening, as well as the true magnitude of the effect i.e. unaffected by averaging with areas where this effect does not operate. Thomas et al. [Nature, 2000] reported a wide range of morphologies on the southern residual CO$_2$ ice cap. We will report on correlations between geomorphology and this brightening behavior. High-resolution imagery [Thomas et al., Nature, 2000] shows that the surface of the northern residual cap has an extremely rough but homogenous texture at length scales of a few meters. This contrasts sharply with its smooth appearance at longer length scales. The variation in the reflectance of this surface at various incidence angles indicates the relief of this texture as the fraction of the field of view that is shadowed varies with incidence angle. The thickness of the northern residual cap is unconstrained and a measurement of the relief of these features would provide a minimum bound. We will report on how this limit on the northern residual cap thickness varies with location.
UR: http://www.gps.caltech.edu/$\sim$shane
DE: 5416 Glaciation
DE: 5462 Polar regions
DE: 5494 Instruments and techniques
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting