Planetary radar studies

A catalog of lunar and radar anomalies was generated to provide a base for comparison with Venusian radar signatures. The relationships between lunar radar anomalies and regolith processes were investigated, and a consortium was formed to compare lunar and Venusian radar images of craters. Time was scheduled at the Arecibo Observatory to use the 430 MHz radar to obtain high resolution radar maps of six areas of the lunar suface. Data from 1978 observations of Mare Serenitas and Plato are being analyzed on a PDP 11/70 computer to construct the computer program library necessary for the eventual reduction of the May 1981 and subsequent data acquisitions. Papers accepted for publication are presented

Investigating The Retention Of Bright And Dark Ejecta From Small Rayed Craters On Mars

Thesis (Ph.D.) University of Alaska Fairbanks, 2010Impact cratering is one of the principal geologic processes operating throughout the solar system. On Mars, small rayed impact craters (SRC) form continuously and randomly on the surface. Ejecta retention, the timespan and ability of excavated ejecta to remain in place around a crater rim, records a lineage of recent surface processes. However, the timescales under which small rayed craters are produced and their origin, whether terrestrial or cosmic, plays an important role in further investigating surface processes and possible recent climate variations. By examining thousands of randomly chosen panchromatic images from the Mars Orbiter Camera Narrow Angle (MOCNA) camera, a population of 630 SRC was catalogued across three equatorial and two polar regions on Mars. The survey of MOCNA images also revealed intriguing Enigmatic Linear Features (ELFs) in the northern hemisphere of Mars, which a short side study revealed to be a unique form of dust-devil track. From statistically examining several physical parameters, dust deposition and periglacial erosion were found to be the major factors affecting ejecta retention for the SRC. SRC morphology revealed ejecta retention sequences that followed four stages of ejecta retention from the initial impact to eventual erasure from the surface. By reconstructing the current cratering rate from estimates of atmospheric filtering, it was possible to calculate the ejecta retention age across Mars. In general, SRC ejecta are retained on the surface for <100 ka. Based on ejecta morphology and retention age estimates, a possible shift from depositional to erosional processes just south of the Martian equator is suspected to have occurred within this timeframe

Cratering Experiments on the Self Armoring of Coarse-Grained Granular Targets

Recently published crater statistics on the small asteroids 25143 Itokawa and 433 Eros show a significant depletion of craters below approx. 100 m in diameter. Possible mechanisms that were brought up to explain this lack of craters were seismic crater erasure and self armoring of a coarse, boulder covered asteroid surface. While seismic shaking has been studied in this context, the concept of armoring lacks a deeper inspection and an experimental ground truth. We therefore present cratering experiments of glass bead projectiles impacting into granular glass bead targets, where the grain sizes of projectile and target are in a similar range. The impact velocities are in the range of 200 to 300 m/s. We find that craters become fainter and irregular shaped as soon as the target grains are larger than the projectile sizes and that granular craters rarely form when the size ratio between projectile and target grain is around 1:10 or smaller. In that case, we observe a formation of a strength determined crater in the first struck target grain instead. We present a simple model based on the transfer of momentum from the projectile to this first target grain, which is capable to explain our results with only a single free parameter, which is moreover well determined by previous experiments. Based on estimates of typical projectile size and boulder size on Itokawa and Eros, given that our results are representative also for km/s impact velocities, armoring should play an important role for their evolution.Comment: accepted for publication in Icaur

The geophysical evolution of impact basins and volcanic structures on Mercury and the Moon

The geologic histories of most terrestrial bodies are dominated by two major processes: meteorite bombardment and volcanism. The forms that the resulting impact craters and volcanic structures take can tell us a great deal about the ways in which these processes occur and about the environment of the host body at the time of their formation. The surfaces of bodies like Mercury and the Moon are old, however, and most such features formed more than a billion years in the past. Impact craters and volcanic structures are thus generally not visible in their original states, but instead in a form which has evolved over geologic time. ^ In this work, I combine observations of planetary surfaces from spacecraft like MESSENGER and GRAIL with modern numerical modeling techniques in order to explore the various ways in which the long-term geophysical evolution of impact craters and volcanic structures can reveal information about the subsurface environment. I find that the pattern of fractures on the floors of the Rachmaninoff, Raditladi, and Mozart peak-ring impact basins on Mercury reveals the contours of the underlying terrain; that the present-day gravitational and topographic signatures over Orientale Basin emerged due to a combination of syn- and post-impact processes which can help to constrain both the parameters of the impact and the rheology of the lunar mantle; and that the tremendous sizes at which lunar lava tubes can be stable open up both new ways of interpreting GRAIL observations of the lunar gravity field and new possibilities for human exploration of the Moon

Report of Workshop on Methodology for Evaluating Potential Lunar Resources Sites

The type and quantity of lunar materials needed to support a space power satellite program was used to define the type and quality of geological information required to certify a site for exploitation. The existing geological, geochemical, and geophysical data are summarized. The difference between these data and the required data for exploitation is used to define program requirements. Most of these requirements involve linear extensions of existing capabilities, fuller utilization of existing data, or expanded use of automated systems

Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained