Initial Results from MGS Pass 3: MOLA Capture Orbit Calibration Data
Press Release Figures from First Mars Global Surveyor
Science Press Conference, October 2, 1997
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"Picket fence" rendition of surface topography in the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter (MOLA). The profile was obtained during the Mars Global Surveyor Capture Orbit Calibration Pass on September 15, 1997. The profile runs from 73°N to 10°S latitude and passes through the topographically subdued northern plains, the western part of the Elysium volcanic province, which shows 3 miles (5 kilometers) of relief, and the
chaotic "dichotomy" boundary between the northern plains and ancient
southern highlands. The MOLA profile is approximately 3000 miles (5000 kilometers) long and has a resolution on the surface of 1000 feet (330 meters) and a vertical resolution of approximately 3 feet (1 meter). (Credit: MOLA Science Team)
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Topographic profile across the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter (MOLA). The profile was obtained during the Mars Global Surveyor Capture Orbit Calibration Pass on September 15, 1997 and represents 20 minutes of data collection. The profile has a length of approximately 3000 miles (5000 kilometers). The large bulge is the western part of the Elysium rise, the second largest volcanic province on Mars, and shows over 3 miles (5 kilometers) of vertical relief. This area contains deep chasms that reflect tectonic, volcanic and erosional processes. In contrast is the almost "featureless" northern plains region of Mars, which shows only hundreds of meters of relief at scales the size of the United States. Plotted for comparison is the elevation of the Viking Lander 2 site, which is located 275 miles (445 kilometers) west of the profile. At the southernmost extent of the trace is the transition from the northern plains to the ancient southern highlands. Characterizing the fine-scale nature of topography in this chaotic region is crucial to testing theories for how the dichotomy between the geologically distinctive northern lowlands and southern uplands formed and subsequently evolved. The spatial
resolution of the profile is approximately 1000 feet (330 meters) and the vertical resolution is approximately 3 feet (1 meter). When the Mars Global Surveyor mapping mission commences in March, 1998, the MOLA instrument will collect 72 times as much data every day for a period of two years. (Credit: MOLA Science Team)
Among the myriad of interesting landforms sampled by MOLA on its first traverse
across the Red Planet on 15 September 1997 is this 13-mile (21-kilometer) diameter impact crater located at ~ 48°N. The figure shows the topography, the computed position of the spacecraft groundtrack (solid line) and the track adjusted to correct for image location error (dashed line). The topographic profile provides some of the first indications of how landscape modification has operated in Martian geologic history. The relief of the crater rim, in combination with the steepness (over 20°) of the inner crater wall, are intriguing in that most craters of this size are much more subdued. The shape of the outer ejecta blanket of the crater likely indicates impact into an H2O-rich crust. Issues concerning how craters such as this can be used to understand the properties of the uppermost crust of Mars in regions where the role of water and other volatiles may be important can be addressed with the high spatial and vertical resolution topographic profiles that will be acquired by MOLA once it
starts its detailed mapping of the Red Planet in March of 1998. (Credit: MOLA Science Team)
Comparison of the cross-sectional relief of the deepest portion of the Grand Canyon (Arizona) on Earth versus a Mars Orbiter Laser Altimeter (MOLA) view of a common type of chasm on Mars in the western Elysium region. The MOLA profile was collected during the Mars Global Surveyor Capture Orbit Calibration Pass on September 15, 1997. The Grand Canyon topography is shown as a trace with a measurement every 295 feet (90 meters) along track, while that from MOLA reflects measurements about every 970 feet (400 meters) along track. The slopes of the steep inner canyon wall of the Martian feature exceed the angle of repose, suggesting relative youth and the potential for landslides. The inner wall slopes of the Grand Canyon are less than those of the Martian chasm, reflecting the long period of erosion necessary to form its mile-deep character on Earth. (Credit: MOLA Science Team)
Other Charts of Interest from Pass 3
Plot of the groundtrack of the MOLA calibration pass.
(Click here to download a postscript plot.) The predicted profile location is based on the actual navigation trajectory that was used to set the MOLA tracking parameters. The profile was located just west of the Elysium Mons volcano, cross through the Elysium Fossae, and traverse the enigmatic boundary of the hemispheric dichotomy.
Plot of the full uncorrected Pass 3 dataset. The blue line corresponds to the range of the
Mars Global Surveyor (MGS) spacecraft to the Martian surface as measured by MOLA. The elliptical shape is due to the capture orbit. The red and green lines correspond to the range gates which bound the
period of time that return pulses were expected at the MOLA receiver.
The gating is used to exclude from the detector background noise at the
laser wavelength. (Credit: MOLA Science Team)
Comparison of Mars elevations from MOLA (black points) with previous estimates of Mars topography along the groundtrack of the Mar Global Surveyor Capture Orbit Science Pass. Shown is the USGS Digital Terrain Model [Wu et al., 1991] (green line), an eighth degree and order spherical harmonic model [Smith and Zuber, 1996] that emphasizes long wavelength vertical control, and individual Mariner 9 and Viking orbiter occultation measurements (red dots) that lie within about 100 km of the MOLA track [Smith and Zuber, 1996]. (Credit: MOLA Science Team)
Direct inquiries to: dsmith@tharsis.gsfc.nasa.gov