What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earth’s “Sister” Planet

Venus is Earth’s closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth’s sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years.The oxygen isotope composition of Venus is currently unknown. However, this single measurement (Δ17O) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Δ17O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide.Determining the Δ17O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Δ17O, this would favour the classic, lower energy, giant impact scenario.We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered.Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a “Grab and Go” strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, “vacuum-cleaner” device) to ensure success. Surface operations would take no longer than one hour.Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth’s planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems

Interpreting the Image of the Human Body in Premodern India

This paper sets out two main arguments. In part one, a description of the adherents of the various intellectual disciplines and religious faiths in premodern India is given, each having developed distinct and different imagined bodies; for example, the body described in Tantric circles had little or nothing in common with the body described in medical circles. In part two, an account is given of the encounter between Ayurvedic anatomy and early colonial European anatomy which led initially to attempts at synthesis; these gave way to an abandonment of the syncretist vision of the body and the acceptance of an epistemological suspension of judgment, in which radically different body conceptualizations are simultaneously held in unacknowledged cognitive dissonance

MODE OF DELIVERY DECISIONS AMONG HIV -INFECTED MOTHERS AT AN URBAN MATERNITY HOSPITAL IN KENYA

Objectives: To quantify the use of elective Caesarean section (ECS) for prevention of mother-to-child transmission of HIV (PMTCT) at an urban Kenyan maternity hospital, to describe mode of delivery decision making among HIV positive women, and to understand patient knowledge and attitudes regarding ECS for PMTCT.Design: Descriptive cross-sectional study.Setting: Pumwani Maternity Hospital, Nairobi, Kenya.Subjects: Two hundred and fifty postpartum HIV-infected women.Main outcome measures: ECS delivery rate, correlates of mode of delivery decisions and ECS for PMTCT knowledge and attitudesResults: The rate of delivery by ECS for PMTCT was 4.0% (10/250), though 13.6% (34/250) planned this mode of delivery. Patient education regarding ECS for PMTCT was limited, and 64% (160/250) of participants had never heard of ECS. Planning ECS for PMTCT was positively correlated with attending clinic at PMH (OR=9.12, 95% CI: 2.94-28.28, p<0.001), knowledge of ECS (OR=27.22, 95% CI: 5.04-148.20, p<0.001)and having a history of abdominal surgery (OR=30.96, 95% CI: 6.32-205.02, p<0.001).Delivering by ECS was associated with planning this mode of delivery (OR=19.52, 95% CI: 3.69-103.23, p<0.001). Planning but not delivering by ECS was mostly due to labourbefore scheduled ECS (55.6%, 15/27) or poor patient understanding of the intervention (29.6%,8/27). After education on ECS for PMTCT, 48.0% (120/250) of participants would consider elective Caesarean section if offered, though cost represented a significant barrier to acceptability.Conclusions: Knowledge and utilisation of ECS for PMTCT are limited and varied in this patient population. ECS may be an acceptable mode of delivery for some Kenyan women, especially if the burden of cost is removed. A clear policy on ECS counselling and utilisation is urgently needed to ensure consistent and appropriate use of thisPMTCT intervention in Kenya