Publications

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.

Today, humans explore deep-space locations such as Mars, asteroids, and beyond, vicariously here on Earth, with noteworthy success. However, to achieve revolutionary breakthroughs that have punctuated history of science since dawn of Space Age has always required humans as the discoverers, as Daniel Boorstin contends in this book of same name. During Apollo 17, human explorers on lunar surface discovered genesis rock, orange glass, and humans in space revamped optically crippled Hubble Space Telescope to enable some of greatest astronomical discoveries of all time. Science-driven human exploration is about developing opportunities for such events, perhaps associated with challenging problems such as whether we can identify life beyond Earth within universe. At issue, however, is how to safely insert humans and spaceflight systems required to allow humans to operate as they do best in hostile environment of deep space. The first issue is minimizing problems associated with human adaptation to most challenging aspects of deep space space radiation and microgravity (or non-Earth gravity). One solution path is to develop technologies that allow for minimization of exposure time of people to deep space, as was accomplished in Apollo. For a mission to planet Mars, this might entail new technological solutions for in-space propulsion that would make possible time-minimized transfers to and from Mars. The problem of rapid, reliable in-space transportation is challenged by celestial mechanics of moving in space and so-called rocket equation. To travel to Mars from Earth in less than time fuel-minimizing trajectories allow (i.e., Hohmann transfers) requires an exponential increase in amount of fuel. Thus, month-long transits would require a mass of fuel as large as dry mass of ISS, assuming existence of continuous acceleration engines. This raises largest technological stumbling block to moving humans on site as deep-space explorers, delivering masses required for human spaceflight systems to LEO or other Earth orbital vantage points using existing or projected fleet of Earth-to-orbit (ETO) launch vehicles. Without a return to Saturn V-class boosters or an alternate path, one cannot imagine emplacing masses that would be required for any deep-space voyage without a prohibitive number of Shuttle-class launches. One futurist solution might involve mass launch systems that could be used to move consumables, including fuel, water, food, and building materials, to LEO in pieces rather than launching integrated systems. This approach would necessitate development of robotic assembly and fuel-storage systems in Earth orbit, but could provide for a natural separation of low-value cargo (e.g., fuel, water).

The north polar residual ice deposits of mars are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter images. A handful of possible impact features were identified, but available data were inconclusive. Determining the number and current topographic characteristics of any craters on the polar residual ice surface is important in constraining the surface age, relative importance of polar cap resurfacing processes and ice flow dynamics, and the role of the cap deposits in the global volatile and climate cycles. Subsequent image processing advances and new Mars Orbiter Laser Altimeter (MOLA) data in the north polar region are now a considerable aid in impact feature identification. This study reconsiders the abundant Viking high-resolution polar images along with the new altimetry data. We examine possible impact features, compare their topography with known mars high-latitude impact features, and use their morphology as a constraint on crater modification processes.

The nature of the Venusian surface was revealed by Pioneer-Venus (PV) observations to be diverse at scales from tens to hundreds of kilometers. Spatial correlations of elevation, surface roughness, and radar reflectivity were investigated as a means of assessing the degree of homogeneity of surface radar properties within topographic provinces and develop a map of possible geologic boundaries. Correlations were performed in a supervised fashion whereby unit boundaries were selected on the basis of statistical and empirical studies of the individual data sets. Interpretations of these units in terms of geologic characteristics are based on the determination of physical units which are model dependent.

The north polar residual ice deposits of mars are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter images. A handful of possible impact features were identified, but available data were inconclusive. Determining the number and current topographic characteristics of any craters on the polar residual ice surface is important in constraining the surface age, relative importance of polar cap resurfacing processes and ice flow dynamics, and the role of the cap deposits in the global volatile and climate cycles. Subsequent image processing advances and new Mars Orbiter Laser Altimeter (MOLA) data in the north polar region are now a considerable aid in impact feature identification. This study reconsiders the abundant Viking high-resolution polar images along with the new altimetry data. We examine possible impact features, compare their topography with known mars high-latitude impact features, and use their morphology as a constraint on crater modification processes.

Global geometric characteristics of topographically fresh impact craters have been assessed, for the first time, from gridded MOLA topography. Global trends of properties such as depth/diameter differ from previous estimates. Regional differences are observed.

Studied features in the northern near polar regions of Mars have morphologies suggesting volcanic origin. The results of this study suggest that these features may represent martian effusive shield volcanics.