HR: 0800h
AN: P31A-0194    [Abstracts]
TI: Summer Season Variability of the North Residual Cap of Mars
AU: * Calvin, W M
EM: wcalvin@unr.edu
AF: University of Nevada, Geological Sciences, MS172, Reno, NV 89557
AU: Titus, T N
EM: ttitus@usgs.gov
AF: U. S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001
AB: Previous observations have noted the change in albedo in a number of north pole bright outliers and in the overall coverage by bright ice deposits between Mariner 9, Viking, and Mars Global Surveyor (MGS) data sets. This effect may be in part due to the affects of global dust storms; however significant within season variation occurred among Viking imagery as well as in Mars Observer Camera (MOC) images within a given Mars summer season. Changes in the cap appearance at the same Ls between MGS years have also been noted. The early season appearance was may depend in part on the presence or absence of large dust events in the previous year, and late season ice extent is generally similar to that observed by Viking but exhibits small-scale inter-year variations that may not be related to globally repeated weather events. We used the bolometric albedo channel of the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor spacecraft to monitor north polar residual ice cap variations between Mars years and within the summer season for three Martian summers between July 1999 and April 2003. For this analysis we have used the visual bolometer data calibrated to albedo by the TES standard data processing pipeline. The data have been binned into 5 degrees of Ls and spatial averages of 1/4 degree in latitude and longitude in order to improve signal to noise. This spatial and seasonal averaging allows a synoptic view of frost migration and mobility within the northern summer season as well as examination of interannual variation of specific terrains. Coverage in the first year is somewhat sparse but still allows comparison with later Mars years. Our analysis focuses on data acquired between Ls 65 and 165, roughly bounding the spring disappearance and fall onset of deposition of the seasonal CO₂ frost. Large scale brightness variations are observed in four general areas: (1) The patchy outlying frost deposits from 90 to 270 east, 75 to 80 north. (2) The large tail below the Chasma Boreal and its associated plateau from 315 to 45 east, 80 to 85 north, that we call the ``Boreale Tongue''. This also includes variations on the end of tongue (Hyperboreae Undae). (3) The troughed terrain in the region from 0 to 120 east longitude (the lower right on a polar stereographic projection) referred to as ``Shackleton's Grooves''. (4) The unit mapped as residual ice in Olympia Planitia. We also note two areas which seem to persist as cool and bright throughout the summer and between Mars years. One is at the source of Chasma Boreal (~15E, 85N) dubbed ``McMurdo'', and the ``Cool and Bright Anomaly (CABA)'' noted by Kieffer and Titus ( Icarus, 154, 162, 2001) at ~330E, 87N called here ``Vostok''. The conversion from albedo to frost coverage includes many parameters. In general lower albedo can imply loss of water ice frost, increase in dust levels or evolution of frost grain size to larger values. We will present preliminary calculations to quantify amount of frost transport and grain size in relation to the albedo variations observed.
DE: 5462 Polar regions
DE: 5464 Remote sensing
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005