Publications

The vertical roughness of the martian surface at ∼250 m spatial scales has been determined in two global latitude bands: an equatorial and a high northern band acquired from 18 tracks of data by the Mars Orbiter Laser Altimeter (MOLA) during the Fall of 1997. The distribution of RMS vertical roughness, as derived from MOLA pulse widths, for the equatorial band is non‐gaussian, with an overall mean of 2.8 m RMS, but with secondary populations at 1.5 m and 2–6 m RMS. The higher latitude northern plains of Mars are almost uniformly ∼1 m RMS in their vertical roughness characteristics, suggesting that they are smoother than virtually any terrestrial deserts. We suggest that dust mantling has muted the local topography of Mars, rendering it as smooth as 1–2 m RMS. Heavily cratered uplands near the martian equator are noticeably rougher, indicating more rugged and less‐mantled local topography.

A lidar system is described that measures laser pulse time-offlight and the distortion of the pulse waveform for reflection from Earth surface terrain features. This instrument system is mounted on a highaltitude aircraft platform and operated in a repetitively pulsed mode for measurements of surface elevation profiles. The laser transmitter makes use of recently developed short-pulse diode-pumped solid-state laser technology. Aircraft position in three dimensions is measured to submeter accuracy by use of differential Global Positioning System receivers. Instrument construction and performance are detailed.

This is a white paper submitted to the Planetary Science and Astrobiology Decadal Survey. The deep atmosphere of Venus is largely unexplored and yet may harbor clues to the evolutionary pathways for a major silicate planet with implications across the solar system and beyond. In situ data is needed to resolve significant open questions related to the evolution and present-state of Venus, including questions of Venus' possibly early habitability and current volcanic outgassing. Deep atmosphere probe-based in situ missions carrying analytical suites of instruments are now implementable in the upcoming decade (before 2030), and will both reveal answers to fundamental questions on Venus and help connect Venus to exoplanet analogs to be observed in the JWST era of astrophysics.

Images of the surface of Venus obtained by the Soviet Venera 9, 10, 13, and 14 landers have been analyzed to provide a basis for understanding the nature of geologic processes operating there. The four spacecraft landed in the Beta‐Phoebe region at median elevations in the upland rolling plains province. The landing points are each separated by distances of more than a thousand kilometers. The Venera panoramas were digitized and transformed into various perspectives in order to facilitate analysis and comparison with other planetary surfaces. Bedrock is exposed at the Venera 10, 13, and 14 sites and is characterized by semicontinuous, flat polygonal to subrounded patches up to several meters in width. The bedrock surface is often dominated by subhorizontal to horizontal layered plates with thicknesses of several centimeters and abundant linear and polygonal vertical fractures. Angular to subangular layered to platy blocks in the 5‐ to 70‐cm range dominate the Venera 9 site and occur much less frequently at the other sites. Blocks appear to share many characteristics with the exposed bedrock and are interpreted to be largely derived from it. Soils (particles <1 cm) are abundant at the Venera 9, 10, and 13 sites but are uncommon at Venera 14. Features indicative of a strong eolian influence (moats, dunes, wind tails) are not observed. A striking aspect of the Venera landing sites is their extreme similarity despite separation distances of thousands of kilometers. Several hypotheses are considered for the origin of the bedrock surfaces, and we investigate in detail the hypothesis that bedrock originated from surface lava flows. In this interpretation, the broadly platy nature of the surface is analogous to the rolling and undulating nature of terrestrial pahoehoe flows caused by the formation and deformation of a semisolid crust. The layering is interpreted to be formed by a combination of upper thermal boundary layer formation and horizontal sheets formed by cooling and shearing during flow emplacement. Vertical fractures are attributed largely to joint patterns formed during cooling. This interpretation made on the basis of surface morphology is consistent with Venera 13 and 14 geochemical results which reported high potassium basalt and tholeiitic basalt compositions, respectively. If this interpretation is correct, large regions of the Beta‐Phoebe area are likely to be characterized by lava flows. The relative freshness of features observed by Venera 14 suggests that some bedrock surfaces are geologically young or that erosion rates are low.

Key science and exploration objectives of lunar robotic precursor missions can be achieved with the Lunar Explorer (LEx) low-cost, robotic surface mission concept described herein. Selected elements of the LEx concept can also be used to create a lunar surface sample return mission that we have called Boomerang.

To prepare for the exploration of Mars by humans, as outlined in the new national vision for Space Exploration (VSE), the Mars Exploration Program Analysis Group (MEPAG), chartered by NASA's Mars Exploration Program (MEP), formed a Human Exploration of Mars Science Analysis Group (HEM-SAG), in March 2007. HEM-SAG was chartered to develop the scientific goals and objectives for the human exploration of Mars based on the Mars Scientific Goals, Objectives, Investigations, and Priorities.1 The HEM-SAG is one of several humans to Mars scientific, engineering and mission architecture studies chartered in 2007 to support NASA s plans for the human exploration of Mars. The HEM-SAG is composed of about 30 Mars scientists representing the disciplines of Mars biology, climate/atmosphere, geology and geophysics from the U.S., Canada, England, France, Italy and Spain. MEPAG selected Drs. James B. Garvin (NASA Goddard Space Flight Center) and Joel S. Levine (NASA Langley Research Center) to serve as HEMSAG co-chairs. The HEM-SAG team conducted 20 telecons and convened three face-to-face meetings from March through October 2007. The management of MEP and MEPAG were briefed on the HEM-SAG interim findings in May. The HEM-SAG final report was presented on-line to the full MEPAG membership and was presented at the MEPAG meeting on February 20-21, 2008. This presentation will outline the HEM-SAG biology and climate/atmosphere goals and objectives. A companion paper will outline the HEM-SAG geology and geophysics goals and objectives.

Precision atmospheric measurements from the Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission will be used to describe columnar chemical variations for a broad range of atomic masses, relative abundances of trace species, and isotope ratios of noble gases. The Gas Processing System (GPS) in DAVINCI’s Venus Mass Spectrometer (VMS) plays a critical role in this characterization. While the GPS is still under development, flow simulations were performed with a simplified computational model to inform trade studies and to examine the nuances of timestamping samples admitted into the Quadrupole Mass Spectrometer (QMS). We use fluid physical parameters to derive temporal signatures for QMS scans, in relation to the altitudes from which samples are retrieved. Samples are considered concomitant when the residence time of “old” atmosphere is minimized. Assuming it is possible to sample across an integrated section of plumbing, preliminary results indicate that the GPS could operate at 95% measurement concomitance with altitude, on average. The method applies to laminar pipe flow, without accounting for thermal convective mixing, Taylor diffusion, or secondary friction losses. For continuous sampling applications, targeting a high level of concomitance alleviates some aspects of data uncertainty that could be associated with temporal smearing.