Surface History of Mercury: Implications for Terrestrial Planets

A working hypothesis of Mercury's history is presented. We infer the surface of Mercury to record a sequence of events broadly similar to those recorded on the moon, implying similar histories of impact bombardment. The oldest terrain so n Mercury seem to be better preserved from modification by ejecta from subsequently formed impact basins because of higher surface gravity. The large lunarlike impact craters on Mercury can be interpreted as part of a distinct episode of bombardment which may have affected all the terrestrial planets about 4 b.y. ago. The light cratering accumulated on the surfaces of the Mercurian smooth plains is similar in diameter/frequency relationship to that of the lunar maria and of the oldest Martian plains units, consistent with recent interpretations of lunar and Martian flux histories by Wetherill(1974) and Soderblom et al. (1974). A straightforward interpretation of the Mercurian surface record thus supports recent order of magnitude increases in age estimates of many Martian features discovered by Mariner 9 but is not conclusive. The large core inferred for Mercury combined with the lack of recognizable evidence of past atmospheric activity is more easily understood in terms of radially heterogeneous accumulation than in terms of differentiation of a homogeneous planet. Early core cooling may be reflected by widespread evidence of crustal shortening. However, Mercury's surface seems little affected by any tectonic, atmospheric, or volcanic processes for the last 3 b.y. or so, raising questions concerning (1) the relationship of the origin of Mercury's magnetic field to that of earth's and (2) the primary cause of volcanic flooding, which may have begun, and ended, approximately synchronously on Mercury and the moon

Preliminary imaging results from the second Mercury encounter

The second Mercury encounter has resulted in the acquisition of about 360 pictures of the south polar regions which provide a reliable cartographic and geologic tie between the two sides of the planet photographed on the first encounter. Stereoscopic coverage of large areas of the southern hemisphere was obtained by combining Mercury 1 and 2 pictures taken at different viewing angles. The south polar regions consist of heavily cratered terrain and intercrater plains interspersed with patches of smooth plains. No large areas of smooth plains similar to those surrounding Caloris occur in the south polar regions. No new types of terrain have been recognized, but lobate scarps are common. The second largest basin seen by Mariner 10 (∼600-km diameter) has been confirmed on the new photography. At high solar elevations the surface displays an abundance of rays and rayed craters

Psychological interventions for distress in adults undergoing haematopoietic stem cell transplantation: a systematic review with meta-analysis

Objectives: To investigate the characteristics, methodology, quality, and efficacy of psychological interventions for distress in adult patients undergoing haematopoietic stem cell transplantation (HSCT). Methods: A systematic review of relevant studies was conducted using six databases with supplementary hand searching. Included studies employed an experimental or quasiexperimental design, interventions included at least one psychological component, and outcomes involved psychological distress in affective terms. Data were abstracted and study quality was assessed using Cochrane Foundation criteria amended to include confounder and common factors control. Data were examined and synthesised using a narrative approach and meta-analysis. Results: Eleven articles for nine interventions met the inclusion criteria out of 11741 abstracts. The studies varied in quality, general, intervention, and methodological characteristics while findings were mixed. Interventions tended to show better efficacy when incorporating a major psychological component involving cognitive behavioural or emotional processing methods with substantial interventionist input. However, this was also associated with methodological limitations and threats to internal validity such as poor confounder and common factors control. A meta-analysis yielded a small but significant pooled effect size estimate in favour of interventions with inconsequential heterogeneity. Risk of bias remained a concern. Conclusions: Psychological interventions may provide some benefit in alleviating distress in HSCT but conclusions remain tentative in light of methodological limitations and risk of bias. Further research is needed to evidence the individual contribution of intervention components and mechanism of change together with improving intervention efficiency and methodological quality

UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Performance assessments, for radioactive waste repositories: the rate of movement of faults

Open-File Report 1982 This report is preliminary and" has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the USGS. Abstract Performance assessments of mined repositories for radioactive waste require estimates of the likelihood of fault movements and earthquakes that may affect the repository and its surrounding ground water flow system. Some previous assessments have attempted to estimate the rate of formation of new faults; some have relied heavily on historic seismicity or the time of latest movement on faults. More appropriate emphasis is on the identification of faults that have been active or may have been active under the present teconic regime in a broad region and on estimates of the long-term rate of movement of such faults. Faults that have moved under the current stress field, even at low rates, are likely to move again during the time the wastes will remain toxic. A continuum exists for the present rate of movement of faults which ranges from 10 mm per year for obviously active faults along the western margin of the North American plate to as low as 10~4 mm per year for recently documented faults in the Atlantic Coast province. On the basis of regional consistency in movement rates and constraints imposed by geomorphology, I derive upper bounds for the rates of occurrence of fault offsets for various crustal stress provinces in the conterminous United States. These upper bounds are not meant to substitute for detailed studies of specific faults and seismicity at specific sites. They can help to reduce the considerable uncertainty that attaches to all estimates of future tectonic activity. The principal uncertainty in their estimation is the manner in which total slip across faults is distributed among discrete events especially in regions in which the rate of movement is very low

Venus: Atmospheric Motion and Structure from Mariner 10 Pictures

The Mariner 10 television cameras imaged the planet Venus in the visible and near ultraviolet for a period of 8 days at resolutions ranging from 100 meters to 130 kilometers. The general pattern of the atmospheric circulation in the upper tropospheric/lower stratospheric region is displayed in the pictures. Atmospheric flow is symmetrical between north and south hemispheres. The equatorial motions are zonal (east-west) at approximately 100 meters per second, consistent with the previously inferred 4-day retrograde rotation. Angular velocity increases with latitude. The subsolar region, and the region downwind from it, show evidence of large-scale convection that persists in spite of the main zonal motion. Dynamical interaction between the zonal motion and the relatively stationary region of convection is evidenced by bowlike waves

Mariner 10 Pictures of Mercury: First Results

Mercury has a heavily cratered surface containing basins up to at least 1300 kilometers diameter flooded with mare-like material. Many features are closely similar to those on the moon, but significant structural differences exist. Major chemical differentiation before termination of accretion is implied