Participation in the Mars Orbiting Laser Altimeter Experiment

This NASA Grant, 5-4434, has covered the active participation of the Principal Investigator, Prof. Gordon Pettengill, and his Co-Investigator, Peter Ford, in the Mars Orbiting Laser Altimeter (MOLA) Experiment, over a period of five years. This participation has included attending team meetings, planning observing operations, developing data-reduction software algorithms, and processing data, as well as presenting a number of oral reports at scientific meetings and published papers in refereed journals. This research has concentrated on the various types of Martian clouds that were detected by the laser altimeter

Research Participation in the Mars Orbiter Laser Altimeter Experiment

This report describes the tasks that have been completed by the Principal Investigator, Gordon Pettengill, and his team during the first year of this grant. Dr. Pettengill was assisted by Dr. Peter Ford and Ms. Joan Quigley. Our main task has been to analyze the polar clouds detected by MOLA (Mars Orbiter Laser Altimeter) during the nominal mission of the Mars Global Surveyor (MGS) in 1999-2001 and to correlate the results with other data sets, in particular that from TES, the MGS thermal emission spectrometer. Starting with the Martian cloud database that we constructed prior to the start of this grant, we have examined all TES footprints that overlap MOLA clouds in time and space, correlating the thermal signature against specific categories that we assign to MOLA clouds on the basis of visual inspection. We are particularly interested in clouds in the region of "cold spots", areas of anomalously low thermal brightness temperature that have been detected in the polar winter by several instruments beginning with IRIS on Mariner 9. They are thought to indicate regions of active CO2 sublimation or snowfall, and it is hoped that MOLA measurements may tell us more about these regions

A Conversation with Gordon H. Pettengill

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Magellan: Electrical and Physical Properties of Venus' Surface

Magellan probes Venus' surface by 12.6-cm-wavelength vertical and oblique radar scattering and measures microwave thermal emission. Emissivity and root-meansquare slope maps between 330° and 30°E and 90°N and 80°S are dissimilar, although some local features are exceptions. Inferred surface emissivities typically are ∼0.85, but vary from ∼0.35 at Maxwell to ∼0.95 northeast of Gula Mons and other locations. Lowest emissivities appear in topographically high areas; this relation suggests that a phase change or differences in chemical weathering occur at about 6055-kilometer radius. Initial results indicate that there are significant variations in the surface scattering function

Observations of the North Polar Region of Mars from the Mars Orbiter Laser Altimeter

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H_(2)O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 × 10^6 to 1.7 × 10^6 cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO_2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

The Global Topography of Mars and Implications for Surface Evolution

Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers