39 results
Canadian Stroke Best Practice Recommendations: Acute Stroke Management, 7th Edition Practice Guidelines Update, 2022
- Manraj Heran, Patrice Lindsay, Gord Gubitz, Amy Yu, Aravind Ganesh, Rebecca Lund, Sacha Arsenault, Doug Bickford, Donnita Derbyshire, Shannon Doucette, Esseddeeg Ghrooda, Devin Harris, Nick Kanya-Forstner, Eric Kaplovitch, Zachary Liederman, Shauna Martiniuk, Marie McClelland, Genevieve Milot, Jeffrey Minuk, Erica Otto, Jeffrey Perry, Rob Schlamp, Donatella Tampieri, Brian van Adel, David Volders, Ruth Whelan, Samuel Yip, Norine Foley, Eric E. Smith, Dar Dowlatshahi, Anita Mountain, Michael D. Hill, Chelsy Martin, Michel Shamy
-
- Journal:
- Canadian Journal of Neurological Sciences / Volume 51 / Issue 1 / January 2024
- Published online by Cambridge University Press:
- 19 December 2022, pp. 1-31
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
The 2022 update of the Canadian Stroke Best Practice Recommendations (CSBPR) for Acute Stroke Management, 7th edition, is a comprehensive summary of current evidence-based recommendations, appropriate for use by an interdisciplinary team of healthcare providers and system planners caring for persons with an acute stroke or transient ischemic attack. These recommendations are a timely opportunity to reassess current processes to ensure efficient access to acute stroke diagnostics, treatments, and management strategies, proven to reduce mortality and morbidity. The topics covered include prehospital care, emergency department care, intravenous thrombolysis and endovascular thrombectomy (EVT), prevention and management of inhospital complications, vascular risk factor reduction, early rehabilitation, and end-of-life care. These recommendations pertain primarily to an acute ischemic vascular event. Notable changes in the 7th edition include recommendations pertaining the use of tenecteplase, thrombolysis as a bridging therapy prior to mechanical thrombectomy, dual antiplatelet therapy for stroke prevention,1 the management of symptomatic intracerebral hemorrhage following thrombolysis, acute stroke imaging, care of patients undergoing EVT, medical assistance in dying, and virtual stroke care. An explicit effort was made to address sex and gender differences wherever possible. The theme of the 7th edition of the CSBPR is building connections to optimize individual outcomes, recognizing that many people who present with acute stroke often also have multiple comorbid conditions, are medically more complex, and require a coordinated interdisciplinary approach for optimal recovery. Additional materials to support timely implementation and quality monitoring of these recommendations are available at www.strokebestpractices.ca.
Geospatial analysis of a COVID-19 outbreak at the University of Wisconsin–Madison: potential role of a cluster of local bars
- Jeffrey E. Harris
-
- Journal:
- Epidemiology & Infection / Volume 150 / 2022
- Published online by Cambridge University Press:
- 05 April 2022, e76
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
We combined smartphone mobility data with census track-based reports of positive case counts to study a coronavirus disease 2019 (COVID-19) outbreak at the University of Wisconsin–Madison campus, where nearly 3000 students had become infected by the end of September 2020. We identified a cluster of twenty bars located at the epicentre of the outbreak, in close proximity to campus residence halls. Smartphones originating from the two hardest-hit residence halls (Sellery-Witte), where about one in five students were infected, were 2.95 times more likely to visit the 20-bar cluster than smartphones originating in two more distant, less affected residence halls (Ogg-Smith). By contrast, smartphones from Sellery-Witte were only 1.55 times more likely than those from Ogg-Smith to visit a group of 68 restaurants in the same area [rate ratio 1.91, 95% confidence interval (CI) 1.29–2.85, P < 0.001]. We also determined the per-capita rates of visitation to the 20-bar cluster and to the 68-restaurant comparison group by smartphones originating in each of 21 census tracts in the university area. In a multivariate instrumental variables regression, the visitation rate to the bar cluster was a significant determinant of the per-capita incidence of positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) tests in each census tract (elasticity 0.88, 95% CI 0.08–1.68, P = 0.032), while the restaurant visitation rate showed no such relationship. The potential super-spreader effects of clusters or networks of places, rather than individual sites, require further attention.
7 - Unseen Planetary Interiors
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 114-127
-
- Chapter
- Export citation
-
Summary
The interior structures of the Earth and Moon are determined from seismic data. The existence and sizes of cores in other planets are inferred from observations of planetary sizes, masses, and shapes, which constrain their uncompressed mean densities and moment of inertia factors. Mantle and crust thicknesses can also be estimated from gravity data obtained by orbiting spacecraft. Successful models of planetary interiors constructed from compositional data must be consistent with observed densities and moments of inertia. High-pressure laboratory experiments can constrain the mineralogy of mantles and cores and the partitioning of elements between silicate and metal in the terrestrial planets. The interiors of the giant planets are not well understood, because of uncertainties in their compositions and internal temperatures and pressures. The states of hydrogen and helium in the interiors of Jupiter and Saturn, and the crystalline forms of ices in Uranus, Neptune, and icy satellites, are inferred from experimentally determined or calculated phase diagrams. The giant planets may have small rocky cores, with successive layers of either metallic hydrogen (Jupiter and Saturn) or ices (Uranus and Neptune), and molecular hydrogen. Planetary mantles and cores evolve over geologic time, through cooling and extraction (or reintroduction, in the case of Earth) of crustal components.
1 - Exploring the Solar System
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 1-17
-
- Chapter
- Export citation
-
Summary
We present a brief overview of the planets, moons, dwarf planets, asteroids, and comets – intended as a primer for those with limited or no familiarity with planetary science. The terrestrial planets (Earth, Mars, Venus, and Mercury) are rocky bodies having mean densities that indicate metal cores; the giant planets are composed mostly of hydrogen and helium and can be divided into gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune), based on their physical states. Small bodies, composed of rock and ices, are either differentiated or not, depending on their thermal histories. Each section of this chapter is generally organized in the historical order in which the objects have been explored by spacecraft. We will return to these bodies repeatedly in the book, focusing on understanding their geologic characteristics and materials, and the processes that produced them.
15 - Physical and Chemical Changes:
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 258-275
-
- Chapter
- Export citation
-
Summary
Physical weathering of rocks on bodies other than the Earth occurs mostly through impact fragmentation, producing regoliths. The lunar regolith is finer-grained and contains more agglutinates than asteroidal regoliths, indicating its greater maturity. Mars exhibits both physical and chemical weathering, and its sedimentary deposits superficially resemble those on Earth. However, its basalt-derived sediments differ from those formed from felsic protoliths on Earth, and evaporation of its aqueous fluids is dominated by sulfates, distinct from terrestrial evaporites that are mostly carbonates and halides. On the surfaces of airless bodies, recondensation of vapor produced by micrometeorite impacts accounts for spectral changes, known as space weathering. In the interiors of carbonaceous chondrite asteroids, isochemical reactions of rocks with cold aqueous fluids produced by melting of ice have altered their mineralogy. Thermal metamorphism of dry chondritic asteroids has modified all but near-surface rocks. Hydrothermal metamorphism on Mars, likely associated with large impacts, has produced low-grade mineral assemblages in metabasalts and serpentinites. Conditions at Venus’ surface are severe enough to cause thermal metamorphism, and reactions with rocks may control the composition of the atmosphere. Because all bodies have gravity, some sloping topography, and some unconsolidated materials, mass wasting is among the most common processes modifying planetary surfaces.
4 - Solar System Raw Materials
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 66-79
-
- Chapter
- Export citation
-
Summary
We explain nucleosynthesis in evolving stars and use this foundation to understand the chemical composition of our own star and of the Solar System. Element abundances are determined from the Sun’s spectrum, and from laboratory measurements of the solar wind and chondritic meteorites. The metal-rich Solar System composition reflects the recycling of elements formed in earlier generations of stars. Condensation models of a cooling nebular gas having this composition produced the minerals found in refractory inclusions in chondrites. The deuterium enrichment in organic matter in chondrites suggests that hydrocarbons formed at low temperatures in molecular clouds and were subsequently processed into complex molecules in the solar nebula and in parent bodies. Ices condensed far from the Sun and were incorporated into the giant planets and comets. Element fractionations in the nebula were largely controlled by element volatility or by the physical sorting of solid grains. Separation of isotopes by mass was common in the nebula, although oxygen shows mass-independent fractionation.
12 - Planetary Atmospheres, Oceans, and Ices
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 210-225
-
- Chapter
- Export citation
-
Summary
Planetary volatiles occur in gas, liquid, and solid forms. In this chapter, we will see that the terrestrial planets have secondary atmospheres formed by outgassing of their interiors. The chemical compositions of the atmospheres of Venus and Mars are dominated by CO2, but the Earth’s atmosphere is distinct because CO2 is sequestered in the lithosphere and life has added O2 to the mix. Giant planet atmospheres are mostly hydrogen with some helium. Titan has an atmosphere of N2 and reducing gases, along with seas of hydrocarbons. Mars has briny groundwater and had lakes and possibly oceans in the distant past. Some moons of the giant planets have subsurface oceans. Noble gases and stable isotopes hold keys to the origin and evolution of volatiles. Differences in temperature and pressure cause atmospheric circulation, controlled by planetary rotation and energy transport. Frozen volatiles are common as polar deposits and sometimes permafrost, but they are especially abundant in the outer Solar System, where they may comprise the crusts of giant planet satellites. Volatile behaviors can be described in terms of geochemical cycles. Greenhouse warming has important implications for planetary climates.
17 - Integrated Planetary Geoscience
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 294-315
-
- Chapter
- Export citation
-
Summary
Planetary exploration typically advances in step with technology. Improvements in spatial and spectral resolution yield discoveries that progress from global to regional scales, and exploration on a planet’s surface provides ground truth for remote sensing data and a level of observation and measurement that geologists crave. Samples that can be analyzed in the laboratory provide geochemical and geochronologic information that complements spacecraft data and enhances its interpretation. We illustrate how data at all these scales have been integrated to characterize the complex geology of Mars and to constrain its geologic history.
Copyright page
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp vi-vi
-
- Chapter
- Export citation
Epilogue
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 316-319
-
- Chapter
- Export citation
-
Summary
Only a quarter of a century ago, the only planets known to exist were those orbiting our Sun. Now we know that other stars host extrasolar planets, or “exoplanets.” The earliest discoveries were made using Earth-based telescopes that detected stellar wobbles caused by nearby orbiting planets. To be detectable, these exoplanets must be large and orbit very close to their stars. Using a different method, NASA’s Kepler orbiting space telescope (2009–2013) observed partial eclipses as planets transited in front of stars (Batalha, 2014). Kepler’s high-precision measurements – only possible in space where stars don’t twinkle – have enabled the discovery of ~4000 candidate planets; of these candidates, perhaps 90 percent are thought to be real planets (Lissauer et al., 2014). The list includes nearly 700 multiple planet systems (Figure E.1), and the large numbers imply that these must be very common. Planetary orbits in multi-planet systems are usually coplanar, consistent with their formation within accretion disks (like our own Solar System’s ecliptic plane).
3 - More Toolkits for the Planetary Geoscientist:
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 48-65
-
- Chapter
- Export citation
-
Summary
In addition to spectroscopy, planetary geoscience uses some other tools familiar to most geologists, and some tools that are either unique or involve new twists in how they are employed. We explain how stratigraphic principles are adapted for planets (using strata produced by impacts), how the density of craters can be quantified to derive relative ages of geologic units, and how radioisotope measurements on samples, where available, give absolute ages. We explain how images from orbiting and landed spacecraft are used, along with chronologic and remote-sensing data, to make planetary geologic maps at different scales. We consider various geophysical techniques that are used on spacecraft to obtain information about planetary potential fields, interior structure, and surface topography. We summarize the kinds of extraterrestrial materials that are available for laboratory investigations, and briefly describe the analytical techniques used to characterize their mineralogy, petrology, and geochemistry. We also examine some techniques that are adapted as remote sensing tools for analyses of rocks and soils on planetary surfaces.
13 - Planetary Aeolian Processes and Landforms
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 226-241
-
- Chapter
- Export citation
-
Summary
We describe the near-surface wind profile, its relation to environmental conditions, and how it can be quantified. The freestream wind speed can be converted to a friction wind speed, which relates to the flow at the atmosphere–surface interface and thus to the entrainment of sediment. The minimum wind speed for entrainment of aeolian sediment depends on gravity and grain size, so that threshold wind speed differs for varying planetary conditions. The difference in transport mechanism for grains leads to different depositional morphologies, which provide clues to the wind speed, wind direction, and sediment availability. Erosional landforms likewise provide information on near-surface atmospheric processes and surface sediments, as well as bedrock lithologies. The study of aeolian landforms thus informs our understanding of the atmosphere, surface geology, and sedimentology on other planets.
9 - Planetary Structures and Tectonics
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 150-169
-
- Chapter
- Export citation
-
Summary
The surfaces of terrestrial planets and icy satellites have enjoyed deformation marked by faults and folds. We use these geologic structures not only to characterize the morphology of the surfaces, but also to describe the motions, stresses, and deformation processes that created the structures. Ultimately, we can sum these structural data and interpretations to infer the tectonic deformation for large portions of, or even entire, planets and satellites. As we will see, understanding deformation at this large tectonic scale enables us to investigate what is driving overall planet or satellite development. We will also learn that while the expected will happen, conundrums exist too. For example, the rocks of terrestrial planets deform quite differently from the icy shells of the satellites of the gas giants, yet the magnitude of these differences and their causes can surprise us. On the other hand, Venus and Earth are quite similar in many planetary characteristics but have strikingly different tectonic histories, which challenges us to understand why.
11 - Impact Cratering as a Geologic Process
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 190-209
-
- Chapter
- Export citation
-
Summary
Heavily cratered surfaces emphasize the important geologic role of impacts on almost all planetary bodies. Large impacts (referred to as “hypervelocity” to indicate velocities of tens of kilometers per second) produce micro-, meso-, and macroscale deformations that can influence the structures of planetary crusts. Crater morphologies are described as simple, complex, and multi-ring, and correlate with crater size and inversely with gravity of the target body. Crater formation is envisioned in three stages: contact/compression, excavation, and modification, each characterized by different processes and geologic features. Shock metamorphism has affected all Solar System bodies, producing breccias containing planar deformation features, high-pressure polymorphs, and melts. Craters provide the basis for planetary stratigraphy and chronology. Massive impacts on the Earth have potential consequences for damaging the planetary ecosystem and biosphere.
2 - Toolkits for the Planetary Geoscientist:
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 18-47
-
- Chapter
- Export citation
-
Summary
With our preliminary survey of planetary bodies in the Solar System complete, we next turn our attention to developing an understanding of the tools that are used by planetary geologists to study these bodies. In this chapter, we will learn about some of the remote sensing techniques that are most commonly used in planetary geologic exploration. We will focus greatest attention on methods that employ light as the carrier of information about the remote target, but we will also consider some methods that employ the detection of other types of carriers. We will describe techniques that can be used from aircraft flying above the Earth, from spacecraft orbiting planets, and from landed and roving platforms on other worlds. We will examine both active and passive remote sensing techniques, provide guidance on how to select the right type of remote sensing method for the desired scientific outcome, and discuss the role of a successful ground campaign in the analysis of remote-sensing data when that option is available.
6 - Planetary Heating and Differentiation
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 100-113
-
- Chapter
- Export citation
-
Summary
We explain how heat is produced by radioactive decay, segregation and exothermic crystallization of metallic cores, impacts, and tidal forces. Planetesimals in the early Solar System were most affected by the decay of short-lived radionuclides. Larger, rocky planets were heated primarily by large impacts and core segregation. Because rocks are poor conductors, heat retention in rocky bodies is a function of planet size. Large-scale melting to produce magma oceans was likely a common process facilitating differentiation to form cores, mantles, and crusts. Metallic liquids are probably necessary for core segregation. Primary crusts, formed during planetary differentiation, are rarely preserved. Mantles are residues from the extraction of silicate crustal melts and core materials. Differentiation of the giant planets was driven by density variations in high-pressure forms of gases, ices, and rock more than by heating and melting. The importance of the various planetary heat sources changes over time; in modern planets the effective heat sources are decay of long-lived radioisotopes and, for the Earth, exothermal crystallization of the liquid outer core.
Contents
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp ix-xiv
-
- Chapter
- Export citation
8 - Planetary Geodynamics
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 128-149
-
- Chapter
- Export citation
-
Summary
Planetary bodies dynamically respond to applied stresses. Heat transfer out of the interior commonly leads to stresses that affect the surface. For quantitative analysis of geodynamics, numerical techniques are generally required and are applied looking at the material as a continuum. Rocks and ice in planetary bodies ultimately want to be in equilibrium with applied stresses. Equilibrium can be assessed by computing whether the stress gradients balance the applied force. The material response to stress is strain, which can be calculated from displacement gradients throughout the material. Stress and strain in a solid are related through intrinsic material properties (e.g., Young’s modulus and Poisson’s ratio). The material properties of rock and ice are similar enough that the icy lithospheres of the moons of the outer planets undergo the same basic processes as the rocky lithospheres of the terrestrial planets. Large lithospheric blocks are supported isostatically, floating in the asthenosphere. Topography can also be supported by the strength of the lithosphere, in which case some amount of flexure occurs as a result of the load on the surface. The distribution of mass in the subsurface can be inferred from measurements of the gravity field. From such measurements, it is possible to discern if a feature such as a mountain or volcano has a large root, or if a large mass lies beneath a surface with no topography (e.g., lunar mascons). Surface temperature is controlled for most planetary surfaces by solar heating, the effect of which generally only penetrates a few meters into the surface. Heat flows through the brittle lithosphere by conduction, but the deeper asthenosphere transfers heat through convection. The asthenosphere behaves like a fluid on geologic timescales, and its response to stress must be investigated in terms of fluid mechanics. The exact response to stress, or the rheology, depends on many factors, including temperature, composition, grain size, and the magnitude of stress. The ductile behavior of the interior is coupled to the surface, enabling geodynamicists to use observations of the surface to infer properties of the interior.
Brief Contents
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp vii-viii
-
- Chapter
- Export citation
5 - Assembling Planetesimals and Planets
- Harry Y. McSween, Jr, University of Tennessee, Knoxville, Jeffrey E. Moersch, University of Tennessee, Knoxville, Devon M. Burr, University of Tennessee, Knoxville, William M. Dunne, University of Tennessee, Knoxville, Joshua P. Emery, University of Tennessee, Knoxville, Linda C. Kah, University of Tennessee, Knoxville, Molly C. McCanta, University of Tennessee, Knoxville
-
- Book:
- Planetary Geoscience
- Published online:
- 25 June 2019
- Print publication:
- 11 July 2019, pp 80-99
-
- Chapter
- Export citation
-
Summary
We discuss the formation of a dusty accretion disk around an infant star and, from that, the planets. Telescopic observations of young stars suggest planet formation required only a few tens of millions of years, in agreement with a Solar System timescale based on measurements of radioactive isotopes in meteorites. The age of the Solar System, 4.567 billion years, is determined from calcium–aluminum inclusions (CAIs), the first-formed solids. Numerical simulations of planetary accretion further support this timescale and constrain the widths of feeding zones. The compositions of the terrestrial planets are broadly chondritic, but depletions in volatile elements suggest their assembly from already differentiated planetesimals. The ice giants have rocky cores that directly accreted nebular ices, and the even more massive gas giants have ice giant-like cores that swept up nebular gas. Leftover planetary building blocks – asteroids and comets – provide more detailed insights into planet formation processes. We complete this story by discussing the origin of the Moon by a giant impact, and the related topic of orbital perturbations possibly caused by migrations of the giant planets.
![](/core/cambridge-core/public/images/lazy-loader.gif)