Geological Mapping of the Debussy Quadrangle (H-14) - Preliminary Results

Geological mapping of Mercury is essential to build an understanding of the history of the planet and to set the context for observations by BepiColombo [1]. Geological mapping of the Debussy quadrangle (H-14) is now underway as part of a program to map the entire planet at a scale of 1:3M using MESSENGER data [2]. The quadrangle is located in the southern hemisphere of Mercury at 0o – 90o E and 22.5o – 65o S. This will be the first high resolution map of the quadrangle as it was not previously imaged by Mariner 10

Post-deposition (and ongoing?) modification of Caloris ejecta blocks

Mercury’s circum-Caloris region hosts numerous kilometer-scale knobs. If these land-forms, peculiar to Caloris, are its ejecta, then they can provide insight into the deep materials of the planet

Geological mapping of the Hokusai (H05) quadrangle of Mercury: Status update

[Introduction] MESSENGER data are being used to construct ~1:3M scale quadrangle geological maps of Mercury. Here, we present our progress mapping the Hokusai (H05) quadrangle

A Dangerous Weapon in the Researcher's Armory : DIY Digitization in the Study of Social History

Despite their penchant for studying revolutions, historians rarely find themselves in the midst of them; changes of leadership and new administrative structures at universities rarely prove to be as revolutionary as predicted. Yet we are in the midst of a digital revolution that is changing the way we find source material, collect and store our sources, read and interpret them, present and publish them and use them to teach our students. There are few other revolutions in the history of our profession that compare in terms of the implications for how, what and why we research. The way we access primary source material has changed the environment of archives dramatically. Archives have become photography studios, sites from which sources are copied and removed rather than places to think, work and reflect. The occasional request for a photocopy of a key document has converted into the mass evacuation of whole archives through the lens of a digital camera. Fellow researchers are momentary companions in this process rather than longer term associates sharing coffee and ideas during well-earned breaks. Archivists have become gatekeepers to a digitized and privatized research process carried out mainly in the isolation of the office or the home study rather than in quiet, if sometimes disturbed, contemplation surrounded by other enquiring academics. Yet this has, on the whole, been a silent revolution. There has been very little in the way of discussion beyond the corridors and common rooms of history departments. Predictably—and fittingly—the more public of these conversations have occurred in online blogs and discussion forums. Now is, perhaps, a good time to reflect in a more consistent and sustained manner on this revolution. That is the objective of this chapter. The focus here is on one researcher’s experience of DIY digitization in the early stages of this revolution, during a collaborative social history project conducted with Professor Henry French (University of Exeter) and Dr Jennifer Jordan between 2007 and 2010. The process of personally accessing, collecting, analysing and interpreting the primary source evidence is my concern here, rather than the use of existing online sources, data storage, the use of meta-data or online publications of sources

Constructional Volcanic Edifices on Mercury: Candidates and Hypotheses of Formation

Mercury, a planet with a predominantly volcanic crust, has perplexingly few, if any, constructional volcanic edifices, despite their common occurrence on other solar system bodies with volcanic histories. Using image and topographical data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, we describe two small (< 15 km‐diameter) prominences with shallow summit depressions associated with volcanically flooded impact features. We offer both volcanic and impact‐related interpretations for their formation, and then compare these landforms with volcanic features on Earth and the Moon. Though we cannot definitively conclude that these landforms are volcanic, the paucity of constructional volcanic edifices on Mercury is intriguing in itself. We suggest that this lack is because volcanic eruptions with sufficiently low eruption volumes, rates, and flow lengths, suitable for edifice construction, were highly spatiotemporally restricted during Mercury's geological history. We suggest that volcanic edifices may preferentially occur in association with late‐stage, post‐impact effusive volcanic deposits. The ESA/JAXA BepiColombo mission to Mercury will be able to investigate further our candidate volcanic edifices, search for other, as‐yet unrecognized edifices beneath the detection limits of MESSENGER data, and test our hypothesis that edifice construction is favored by late‐stage, low‐volume effusive eruptions

Prolonged eruptive history of a compound volcano on Mercury: volcanic and tectonic implications

A 27 × 13 km ‘rimless depression’ 100 km inside the southwest rim of the Caloris 19 basin is revealed by high resolution orbital imaging under a variety of illuminations to 20 consist of at least nine overlapping volcanic vents, each individually up to 8 km in 21 diameter. It is thus a ‘compound’ volcano, indicative of localised migration of the site 22 of the active vent. The vent floors are at a least 1 km below their brinks, but lack the 23 flat shape characteristically produced by piston-like subsidence of a caldera floor or 24 by flooding of a crater bottom by a lava lake. They bear a closer resemblance to 25 volcanic craters sculpted by explosive eruptions and/or modified by collapse into void 26 spaces created by magma withdrawal back down into a conduit. This complex of 27 overlapping vents is at the summit of a subtle edifice at least 100 km across, with 28 flank slopes of about only 0.2 degrees, after correction for the regional slope. This is 29 consistent with previous interpretation as a locus of pyroclastic eruptions. 30 Construction of the edifice could have been contributed to by effusion of very low 31 viscosity lava, but high resolution images show that the vent-facing rim of a nearby 32 impact crater is not heavily embayed as previously supposed on the basis of lower 33 resolution fly-by imaging. Contrasts in morphology (sharpness versus blurredness of 34 the texture) and different densities of superposed sub-km impact craters inside each 35 vent are consistent with (but do not prove) substantial differences in the age of the 36 most recent activity at each vent. This suggests a long duration of episodic 37 magmagenesis at a restricted locus. The age range cannot be quantified, but could be 38 of the order of a billion years. If each vent was fed from the same point source, 39 geometric considerations suggest a source depth of at least 50 km. However, the 40 migration of the active vent may be partly controlled by a deep-seated fault that is 41 radial to the Caloris basin. Other rimless depressions in this part of the Caloris basin 42 fall on or close to radial lines, suggesting that elements of the Pantheon Fossae radial 43 fracture system that dominates the surface of the central portion of the Caloris basin 44 may continue at depth almost as far as the basin rim

Geology of the Hokusai quadrangle (H05), Mercury

The Hokusai (H05) quadrangle is in Mercury’s northern mid-latitudes (0–90°E, 22.5–65°N) and covers almost 5 million km2, or 6.5%, of the planet’s surface. We have used data from the MESSENGER spacecraft to make the first geological map of H05. Linework was digitized at 1:400,000-scale for final presentation at 1:3,000,000-scale, mainly using a ∼166 m/pixel monochrome basemap. Three major photogeologic units of regional extent were mapped: intercrater, intermediate, and smooth plains. Materials of craters ≥ 20 km in diameter were classified according to their degradation state. Two classification schemes were employed in parallel, one with three classes and the other with five classes, for compatibility with existing MESSENGER-era quadrangle maps and the first global geologic map. This map will provide science context and targets for the ESA-JAXA BepiColombo mission to Mercury

Hollows on Mercury: materials and mechanisms involved in their formation

Recent images of the surface of Mercury have revealed an unusual and intriguing landform: sub-kilometre scale, shallow, flat-floored, steep-sided rimless depressions typically surrounded by bright deposits and generally occurring in impact craters. These ‘hollows’ appear to form by the loss of a moderately-volatile substance from the planet’s surface and their fresh morphology and lack of superposed craters suggest that this process has continued until relatively recently (and may be on-going). Hypotheses to explain the volatile-loss have included sublimation and space weathering, and it has been suggested that hollow-forming volatiles are endogenic and are exposed at the surface during impact cratering. However, detailed verification of these hypotheses has hitherto been lacking. In this study, we have conducted a comprehensive survey of all MESSENGER images obtained up to the end of its fourth solar day in orbit in order to identify hollowed areas. We have studied how their location relates to both exogenic processes (insolation, impact cratering, and solar wind) and endogenic processes (explosive volcanism and flood lavas) on local and regional scales. We find that there is a weak correlation between hollow formation and insolation intensity, suggesting formation may occur by an insolation-related process such as sublimation. The vast majority of hollow formation is in localised or regional low-reflectance material within impact craters, suggesting that this low-reflectance material is a volatile-bearing unit present below the surface that becomes exposed as a result of impacts. In many cases hollow occurrence is consistent with formation in volatile-bearing material exhumed and exposed during crater formation, while in other cases volatiles may have accessed the surface later through re-exposure and possibly in association with explosive volcanism. Hollows occur at the surface of thick flood lavas only where a lower-reflectance substrate has been exhumed from beneath them, indicating that this form of flood volcanism on Mercury lacks significant concentrations of hollow-forming volatiles

Decision uncertainty and value of further research: a case-study in fenestrated endovascular aneurysm repair for complex abdominal aortic aneurysms

Background: Fenestrated endovascular aneurysm repair (fEVAR) is a new approach for complex abdominal aortic aneurysms, limited to a few specialist centers, with limited evidence base. We developed a cost-effectiveness decision model of fEVAR compared to open surgical repair (OSR) to investigate the likely direction of costs and benefits and inform further research projects on this technology. Methods: A systematic review with meta-analysis and a four-state Markov model were used to estimate the cost-effectiveness of fEVAR versus OSR. We used a recent coverage with evidence development framework to characterize the main sources of uncertainty and inform decisions about the type of further research that would be most worthwhile and feasible. Results: Seven observational comparative studies were identified, of which four presented odds ratios adjusted for confounders. The odds ratios for operative mortality varied widely between studies. Assuming a central estimate of the odds ratio of 0.54 (95% CI 0.05–6.24), the decision model estimated that the incremental cost per quality adjusted life year (QALY) was £74,580/QALY with a probability of 9 and 16% of being cost-effective at standard cost-effectiveness thresholds of £20,000/QALY and £30,000/QALY, respectively. The Expected Value of Perfect Information over 10 years at a threshold of £20,000/QALY was £11.2 million. Operative mortality contributed to most of the uncertainty in the decision model. Conclusions: In the case of “maturing technologies”, decision modelling indicates the likely direction of costs and benefits and guides the development of further research projects. In our analysis of fEVAR versus OSR, decision uncertainty, particularly around operative mortality, might be effectively resolved by a short-term RCT, or possibly a well-conducted comparative observational study. Decision makers may consider that a conditional coverage decision is warranted with assessments required to make this type of recommendation depending on local priorities and circumstances