Publications

The enigmatic Medusae Fossae Formation (MFF) is one of the youngest surficial deposits on Mars. Previously proposed modes of origin include pyroclastic volcanism, eolian mantling, polar sedimentation, carbonate platform, and paleoshorelines. In order to assess mapped member boundaries and constrain likely origin processes we analyze five topographic transects from the Mars Orbiter Laser Altimeter (MOLA) collected during the aerobraking hiatus orbit period of the Mars Global Surveyor (MGS) mission together with several simultaneously acquired Mars Orbiter Camera (MOC) images to examine the regional and local variations in the relief, slopes, vertical roughness, and relative elevations of mapped MFF members. We find that the members are not particularly flat or level but have average thicknesses of many hundreds of meters and substantially more internal relief than previously thought. Locally, the MFF members are sometimes distinguishable by slope, elevation, and surface roughness characteristics, but no unique formation‐wide characteristics are apparent in this analysis of the limited initial data. The relative elevations of the mapped members are not consistent with undeformed planar horizontal layers but may be consistent with layers draped over preexisting topography with subsequent partial removal. Analysis of the initial coincident MOC and MOLA hiatus data suggests the possible presence of local layers, as well as the mislocation of at least a few MFF member and formation boundaries. We conclude that carbonate and shoreline deposit origins are not as well supported in the initial MGS data as they were in the Viking data and that the MFF formation and member boundaries should be reexamined in conjunction with the incoming new MGS data.

Pioneer Venus radar data on surface properties have been used to compare the Vega spacecraft landing sites with the northern 1/4 of Venus mapped by the orbiters Venera 15 and 16. The regions surrounding both landing sites possess surface reflectivity and small-scale roughness properties most similar to those of mapped volcanoes and volcanic plains regions and different surface properties than those of mapped tectonic units. Regions analogous to the Vega 1 site are relatively rare, covering 2.8% of the mapped surface. Vega 2 analogs are much more common and cover 22.6% of the surface. Neither landing site is representative of the nearby highlands of Aphrodite, but the Vega 2 landing site is similar to much of the northern plains of Venus.

We characterize and model small volcanoes in the martian mid-latitude and near-polar regions. Regional differences and possible latitude-dependent geometry parameters hint that subsurface volatiles may be significant for polar eruptions. Additional information is contained in the original extended abstract.

Recently, an airborne lidar system that measures laser pulse time-of-flight and the distortion of the pulse waveform upon reflection from earth surface terrain features was developed and is now operational. This instrument is combined with Global Positioning System (GPS) receivers and a two-axis gyroscope for accurate recovery of aircraft position and pointing attitude. The laser altimeter system is mounted on a high-altitude aircraft platform and operated in a repetitively-pulsed mode for measurements of surface elevation profiles at nadir. The laser transmitter makes use of recently developed short-pulse diode-pumped solid-state laser technology in Q-switched Nd:YAG operating at its fundamental wavelength of 1064 nm. A reflector telescope and silicon avalanche photodiode are the basis of the optical receiver. A high-speed time-interval unit and a separate high-bandwidth waveform digitizer under microcomputer control are used to process the backscattered pulses for measurements of terrain. Other aspects of the lidar system are briefly discussed.

NASA is in the final throes of implementing the most powerful surface reconnaissance mission ever undertaken to Mars. Dubbed the Mars Science Laboratory (MSL), it represents NASA's first life inference mission equipped with instruments capable of detecting the chemical building blocks of life more than an order of magnitude more sensitive than those used by the Viking mission of the 1970s. MSL will also demonstrate multiple technical capabilities needed to enable a future robotic Mars sample return mission. In his 31 October Letter (“Viewing NASA's Mars budget with resignation,” p. [672][1]), former NASA Associate Administrator S. A. Stern suggested that excessive cost growth of MSL is deeply damaging NASA's overall planetary exploration agenda and destroying the opportunity for a future Mars sample return mission. He blames senior NASA leaders for disbanding his MSL independent technical review team, which he claims forced his resignation. ![Figure][2] Let's roll. Wheels have been fitted to NASA's Mars Science Laboratory (MSL) rover, which is being assembled at NASA's Jet Propulsion Laboratory, Pasadena, California. The rover has a ground clearance of about 60 cm, or 2 feet, and is about the size of a small automobile. CREDIT: NASA/JPL Now is the time to set the record straight. NASA consolidated its independent standing review boards to streamline the process for all major flight programs in 2007. The MSL Standing Review Board remains in effect and was never disbanded. Stern also claims that MSL was “assigned” a cost level of $650 million. He fails to mention when and by whom. The $650 million cost was a placeholder assigned to a medium-class Mars rover mission by the National Research Council Solar System Decadal Survey committee in 2002, before NASA had developed a basis of cost estimate for MSL. This served as input to NASA studies from 2000 to 2004 to fully define the MSL mission and culminated in the competitive selection of its science payload in late 2004. At that time, the overall mission was baselined at a cost of $1.4 billion, not including several costs associated with the radioisotope power system. Given the experience with the cost of the Mars Exploration Rovers and the increased scientific and technical scope of the MSL mission, the so-called assigned value of $650 million is not credible. Stern's own New Horizons flyby mission to Pluto cost NASA more than $650 million; it is unrealistic to expect that a 700-kg analytical laboratory that must soft-land on Mars and drive around with 100 kg of scientific instruments could possibly cost less than a planetary flyby mission. Indeed, MSL's 2 years of intensive surface science operations are difficult to compare to any missions in the $650 million price class given typical science-per-dollar metrics. The established NASA cost to implement MSL as of the time of its confirmation review was $1.55 billion (August 2006), which grew due to NASA-wide issues with thermal protection system materials in 2007 to approximately $1.7 billion. The total cost growth of the MSL mission development since NASA confirmed the mission is typical of other Mars exploration missions successfully flown over the past decade. The cost to fly MSL in 2009 will be less than the cost (in today's dollars) of flying a nonmobile Viking Lander laboratory to Mars, and MSL includes a whole new generation of instruments and mobility. NASA has an exemplary record of honoring its commitments to implement flagship-class missions that frequently “rewrite the textbooks” as they discover how the universe operates. To abandon MSL at this time would represent an unprecedented break with this guiding philosophy. As President John F. Kennedy once stated, we choose to do these things not because they are easy, but because they are hard. NASA succeeded with Apollo to the Moon, Hubble to the universe, and Cassini to Saturn. The agency is ready now to assault the martian frontier with MSL. [1]: /lookup/doi/10.1126/science.322.5902.672b [2]: pending:yes

Two geodetic airborne laser altimeter (ALA) systems coupled to Global Positioning System receivers acquired submeter-resolution topographic profiles of the lower parts of Breidamerkurjökull and Skeidarárjökull, Iceland, in May 1989 and September 1991 (Skeidarárjökull) and of Jakobshavns Isbræ, Greenland, in April 1992. Maximum measured crevasse depths on Breidamerkurjökull, Skeidarárjökull and Jakobshavns Isbræ were 20.7, 36.1 and 50.2 m, respectively. Crevasse spacings were 43 m (45 crevasses km −1 ) for Breidamerkur jökull, 46–51 m (25 crevasses km −1 ) for Skeidarárjökull and 20–40 m (lower part) or 50–80 m (upper part) of Jakobshavns Isbræ (27 crevasses km −1 ). Surface slopes were ~2.4° for the lower 11 km of Breidamerkurjökull, ~0.8° for the lower 10 km of Skeidarárjökull and 1.55° for the lower 28 km of Jakobshavns Isbræ (with a range of 0.55° for the final 17 km to ~6.3° for a steep central part several km in length). Average longitudinal strain-rate values, estimated by assuming a bulk ice temperature of 0°C and a density of 880 kg m −3 , ranged from 0.12 a −1 for Breidamerkurjökull, to 0.63 a −1 for Skeidarárjökull; values for Jakobshavns Isbræ fell between 1.3 and 1.7 a −1 . Remote sensing of glacier microtopography by ALA offers a potential new tool for determining crevasse morphology, spatial density and spacing, meter-scale local slopes, long-wavelength gradients and derived strain rates.

This study focuses on the depth/diameter (d/D) relationships of impact craters within Utopia Basin (25 deg. N - 70 deg. N, 88 deg. W - 150 deg. W), Mars. In order to search for spatial variations in the study area, d/D values for a total of 1,430 craters have been grouped by sub-regions based upon their similar d/D characteristics. This has revealed a significant difference in d/D relationship for craters in north central Utopia basin compared with other parts of the basin, and withother areas on Mars. Preliminary measurements have also been collected in four additional test areas (Acidalia, Sinai, Sirenum, and south of Argyre) for comparison purposes.