Probing Supraglacial Debris on Mars 1: Sources, Thickness, and Stratigraphy

Geomorphic and geophysical evidence supports a debris-covered glacier origin for a suite of landforms at themid-latitudes of Mars, including lobate debris aprons (LDA), lineated valley fill (LVF), and concentric crater fill (CCF). These large reservoirs of ice and their near-surface structure provide a rich record for understanding the planet's climate and history of global volatile exchange over the past billion years. LDA, LVF, and CCF are also potential sites for future robotic and human missions but the accessibility of glacial ice for direct sampling and in situ resource utilization depends largely on the geotechnical properties of the surface debris ("supraglacial debris"), including its thickness, grain sizes, and density structure. The physical properties of this supraglacial debris layer have been poorly constrained. We use images of morphology, digital elevation models, thermal inertia data, and radar sounding data to probe the near surface of LDA, LVF, and CCF in Deuteronilus Mensae in order to place constraints on the sources, grain sizes, thickness, and stratigraphy of supraglacial debris. We find evidence for at least a two-layer stratigraphy. Layered mantle consisting of atmospherically emplaced dust and ice superposes boulder-rich sediment sourced by rockfalls glacially transported downslope. High thermal inertia, boulder-rich termini and debris bands reminiscent of medial moraines are found throughout the study region, supporting a rockfall origin for at least a fraction of the debris exposed at the surface. This supraglacial debris layer would have thickened with time from sublimation of glacial ice and liberation of englacial sediment and dust. At present, the entire supraglacial debris package is a minimum of a few meters in thickness and is likely tens of meters in thickness in many locations, possibly thinning regionally at lower latitudes and locally thinning toward the headwalls. The lack of terracing or interior structures in craters formed within LDA, LVF, and CCF and the absence of near-surface reflectors in SHARAD radar data further suggest that no strong contrasts i

Comparing Volcanic Terrains on Venus and Earth: How Prevalent are Pyroclastic Deposits on Venus?

In the last several years, astronomers have discovered several exoplanets with masses less than 10 times that of the Earth [1]. Despite the likely abundance of Earth-sized planets, little is known about the pathways through which these planets evolve to become habitable or uninhabitable. Venus and Earth have similar planetary radii and solar orbital distance, and therefore offer a chance to study in detail the divergent evolution of two objects that now have radically different climates. Understanding the extent, duration, and types of volcanism present on Venus is an important step towards understanding how volatiles released from the interior of Venus have influenced the development of the atmosphere. Placing constraints on the extent of explosive volcanism on Venus can provide boundary conditions for timing, volumes, and altitudes for atmospheric injection of volatiles. In addition, atmospheric properties such as near-surface temperature and density affect how interior heat and volatiles are released. Radar image data for Venus can be used to determine the physical properties of volcanic deposits, and in particular, they can be used to search for evidence of pyroclastic deposits that may result from explosive outgassing of volatiles. For explosive volcanism to occur with the current high atmospheric pressure, magma volatile contents must be higher than is typical on Earth (at least 2-4% by weight) [2,3]. In, addition, pyroclastic flows should be more prevalent on Venus than convective plumes and material may not travel as far from the vent source as it would on Earth [3]. Areas of high radar backscatter with wispy margins that occur near concentric fractures on Sapho Patera [4] and several coronae in Eastern Eistla Regio [5] have been attributed to collapse of eruption columns and runout of rough materials

Geologic Studies of Planetary Surfaces Using Radar Polarimetric Imaging

Radar is a useful remote sensing tool for studying planetary geology because it is sensitive to the composition, structure, and roughness of the surface and can penetrate some materials to reveal buried terrain. The Arecibo Observatory radar system transmits a single sense of circular polarization, and both senses of circular polarization are received, which allows for the construction of the Stokes polarization vector. From the Stokes vector, daughter products such as the circular polarization ratio, the degree of linear polarization, and linear polarization angle are obtained. Recent polarimetric imaging using Arecibo has included Venus and the Moon. These observations can be compared to radar data for terrestrial surfaces to better understand surface physical properties and regional geologic evolution. For example, polarimetric radar studies of volcanic settings on Venus, the Moon and Earth display some similarities, but also illustrate a variety of different emplacement and erosion mechanisms. Polarimetric radar data provides important information about surface properties beyond what can be obtained from single-polarization radar. Future observations using polarimetric synthetic aperture radar will provide information on roughness, composition and stratigraphy that will support a broader interpretation of surface evolution

Effects of concurrent intravenous morphine sulfate and naltrexone hydrochloride on end-tidal carbon dioxide

<p>Abstract</p> <p>Background</p> <p>Respiratory depression, a potentially fatal side-effect of opioid-overdose, may be reversed by timely administration of an opioid antagonist, such as naloxone or naltrexone. Tampering with a formulation of morphine sulfate and sequestered naltrexone hydrochloride extended release capsules (MS-sNT) releases both the opioid morphine and the antagonist naltrexone. A study in recreational opioid-users indicated that morphine and naltrexone injected in the 25:1 ratio (duplicating the ratio of the formulation) found MS-sNT reduced morphine-induced euphoric effects vs intravenous (IV) morphine alone. In the same study, the effects of morphine + naltrexone on end-tidal carbon dioxide (EtCO₂), a measure of respiratory-depression, were evaluated and these data are reported here.</p> <p>Methods</p> <p>Single-center, placebo-controlled, double-blind crossover study. Non-dependent male opioid users were randomized to receive single IV doses of placebo, 30 mg morphine alone, and 30 mg morphine + 1.2 mg naltrexone. EtCO₂was measured by noninvasive capnography.</p> <p>Results</p> <p>Significant differences in EtCO₂least-squares means across all treatments for maximal effect (E_max) and area under the effect curve (AUE_0-2, AUE_0-8, AUE_0-24) were detected (all p ≤ 0.0011). EtCO₂E_maxvalues for morphine + naltrexone were significantly reduced vs morphine alone (42.9 mm Hg vs 47.1 mm Hg, p < 0.0001) and were not significantly different vs placebo (41.9 mm Hg). Median time to reach maximal effect (TE_max) was delayed for morphine + naltrexone vs morphine alone (5.0 h vs 1.0 h).</p> <p>Conclusions</p> <p>Results provide preliminary evidence that the naltrexone:morphine ratio within MS-sNT is sufficient to significantly reduce EtCO₂when administered intravenously to non-dependent male recreational opioid-users. Further studies with multiple measures of respiratory-function are warranted to determine if risk of respiratory depression is also reduced by naltrexone in the tampered formulation.</p

Beamforming P-Band Synthetic Aperture Radar for Planetary Applications

The Space Exploration Synthetic Aperture Radar (SESAR) is an advanced P-band beamforming radar instrument concept to enable a new class of observations suitable to meet multiple Decadal Survey science goals for planetary exploration. The radar is capable of providing unprecedented surface and near subsurface measurements at full polarimetry and fine (meter scale) resolution, and achieves beam agility through programmable waveform generation and digital beamforming. The radars highly flexible modular architecture employs a novel low power, lightweight design approach to meet stringent planetary instrument requirements, all while minimizing cost and development time

Sedimentary Processes on Venus

The sedimentary cycle, including the processes of erosion, transport, and lithification, is a key part of how planets evolve over time. Early images of Venus’s vast volcanic plains, numerous volcanoes, and rugged tectonic regions led to the interpretation that Venus is a volcanic planet with little sediment cover and perhaps few processes for generating sedimentary rocks. However, in the years since the Magellan mission in the 1990s we have developed a better understanding of sedimentary process on Venus. Impact craters are the largest present-day source of sediments, with estimates from the current crater population suggesting an average sediment layer 8–63 cm in thickness if distributed globally. There is clear evidence of fine-grained material in volcanic summit regions that is likely produced through volcanism, and dune fields and yardangs indicate transport of sediments and erosion of rocks through wind. Landslides and fine-grained materials in highland tessera regions demonstrate erosive processes that move sediment downhill. It is clear that sediments are an important part of Venus’s geology, and it is especially important to realize that they mantle features that may be of interest to future landed or low-altitude imaging missions. The sinks of sediments are less well known, as it has been difficult to identify sedimentary rocks with current data. Layering observed in Venera images and in Magellan images of some tessera regions, as well as calculated rock densities, suggest that sedimentary rocks are present on Venus. New data is needed to fully understand and quantify the present-day sedimentary cycle and establish with certainty whether sedimentary rock packages do, in fact, exist on Venus. These data sets will need to include higher-resolution optical and radar imaging, experimental and geochemical measurements to determine how chemical weathering and lithification can occur, and topography to better model mesospheric winds. Sediments and sedimentary rocks are critical to understanding how Venus works today, but are also extremely important for determining how Venus’s climate has changed through time and whether it was once a habitable planet

Pulsed Plasma Thruster Contamination

Pulsed Plasma Thrusters (PPT's) are currently baselined for the Air Force Mightysat II.1 flight in 1999 and are under consideration for a number of other missions for primary propulsion, precision positioning, and attitude control functions. In this work, PPT plumes were characterized to assess their contamination characteristics. Diagnostics included planar and cylindrical Langmuir probes and a large number of collimated quartz contamination sensors. Measurements were made using a LES 8/9 flight PPT at 0.24, 0.39, 0.55, and 1.2 m from the thruster, as well as in the backflow region behind the thruster. Plasma measurements revealed a peak centerline ion density and velocity of approx. 6 x 10(exp 12) cm(exp -3) and 42,000 m/s, respectively. Optical transmittance measurements of the quartz sensors after 2 x 10(exp 5) pulses showed a rapid decrease in plume contamination with increasing angle from the plume axis, with a barely measurable transmittance decrease in the ultraviolet at 90 deg. No change in optical properties was detected for sensors in the backflow region

Feasibility and Compliance with Daily Home ECG Monitoring of the QT Interval in Heart Transplant Recipients

Background: Recent evidence suggests that acute allograft rejection after heart transplantation causes an increased QT interval on electrocardiogram (ECG). The aims of this pilot study were to (1) determine whether heart transplant recipients could achieve compliance in transmitting a 30-second ECG every day for 1 month using a simple ECG device and their home telephone, (2) evaluate the ease of device use and acceptability by transplant recipients, and (3) evaluate the quality of transmitted ECG tracings for QT-interval measurement. Methods: A convenience sample of adult heart transplant recipients were recruited and trained to use the device (HeartOne, Aerotel Medical Systems, Holon, Israel). Lead II was used with electrodes that were easy to slip on and off (expandable metal wrist watch-type electrode for right wrist and C-shaped band electrode for left ankle). Patients used a toll-free number with automated voice prompts to guide their ECG transmission to the core laboratory for analysis. Results: Thirty-one subjects (72% were male; mean age of 52 ± 17 years; 37% were nonwhite) achieved an ECG transmission compliance of 73.4% (daily) and 100% (weekly). When asked, how difficult do you think it was to record and transmit your ECG by phone, 90% of subjects replied “somewhat easy” or “extremely easy.” Of the total 644 ECGs that were transmitted by subjects, 569 (89%) were acceptable quality for QT-interval measurement. The mean QTc was 448 ± 44 ms (440 ± 41 ms for male subjects and 471 ± 45 ms for female subjects). Eleven subjects (35%) had an extremity tremor, and 19 subjects (55%) had ≥ 1+ left leg edema. Neither of these conditions interfered with ECG measurements. Conclusion: Transplant recipients are compliant with recording and transmitting daily and weekly ECGs

Initial Observations of Lunar Impact Melts and Ejecta Flows with the Mini-RF Radar

The Mini-RF radar on the Lunar Reconnaissance Orbiter's spacecraft has revealed a great variety of crater ejecta flow and impact melt deposits, some of which were not observed in prior radar imaging. The craters Tycho and Glushko have long melt flows that exhibit variations in radar backscatter and circular polarization ratio along the flow. Comparison with optical imaging reveals that these changes are caused by features commonly seen in terrestrial lava flows, such as rafted plates, pressure ridges, and ponding. Small (less than 20 km) sized craters also show a large variety of features, including melt flows and ponds. Two craters have flow features that may be ejecta flows caused by entrained debris flowing across the surface rather than by melted rock. The circular polarization ratios (CPRs) of the impact melt flows are typically very high; even ponded areas have CPR values between 0.7-1.0. This high CPR suggests that deposits that appear smooth in optical imagery may be rough at centimeter- and decimeter- scales. In some places, ponds and flows are visible with no easily discernable source crater. These melt deposits may have come from oblique impacts that are capable of ejecting melted material farther downrange. They may also be associated with older, nearby craters that no longer have a radar-bright proximal ejecta blanket. The observed morphology of the lunar crater flows has implications for similar features observed on Venus. In particular, changes in backscatter along many of the ejecta flows are probably caused by features typical of lava flows

Subsurface structure of Planum Boreum from Mars Reconnaissance Orbiter Shallow Radar soundings

We map the subsurface structure of Planum Boreum using sounding data from the Shallow Radar (SHARAD) instrument onboard the Mars Reconnaissance Orbiter. Radar coverage throughout the 1,000,000- km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits (NPLD). A dome-shaped zone of diffuse reflectivity up to 12 ls (1-km thick) underlies twothirds of the NPLD, predominantly in the main lobe but also extending into the Gemina Lingula lobe across Chasma Boreale. We equate this zone with a basal unit identified in image data as Amazonian sand-rich layered deposits [Byrne, S., Murray, B.C., 2002. J. Geophys. Res. 107, 5044, 12 pp. doi:10.1029/2001JE001615; Fishbaugh, K.E., Head, J.W., 2005. Icarus 174, 444–474; Tanaka, K.L., Rodriguez, J.A.P., Skinner, J.A., Bourke, M.C., Fortezzo, C.M., Herkenhoff, K.E., Kolb, E.J., Okubo, C.H., 2008. Icarus 196, 318–358]. Elsewhere, the NPLD base is remarkably flat-lying and co-planar with the exposed surface of the surrounding Vastitas Borealis materials. Within the NPLD, we delineate and map four units based on the radar-layer packets of Phillips et al. [Phillips, R.J., and 26 colleagues, 2008. Science 320, 1182– 1185] that extend throughout the deposits and a fifth unit confined to eastern Gemina Lingula. We estimate the volume of each internal unit and of the entire NPLD stack (821,000 km3), exclusive of the basal unit. Correlation of these units to models of insolation cycles and polar deposition [Laskar, J., Levrard, B., Mustard, J.F., 2002. Nature 419, 375–377; Levrard, B., Forget, F., Montmessin, F., Laskar, J., 2007. J. Geophys. Res. 112, E06012, 18 pp. doi:10.1029/2006JE002772] is consistent with the 4.2-Ma age of the oldest preserved NPLD obtained by Levrard et al. [Levrard, B., Forget, F., Montmessin, F., Laskar, J., 2007. J. Geophys. Res. 112, E06012, 18 pp. doi:10.1029/2006JE002772]. We suggest a dominant layering mechanism of dust–content variation during accumulation rather than one of lag production during periods of sublimation