Ceres internal structure from geophysical constraints          下载免费PDF全文

Scott D. King  Julie C. Castillo‐Rogez  M. J. Toplis  Michael T. Bland  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2018,53(9):1999-2007

Thermal evolution modeling has yielded a variety of interior structures for Ceres, ranging from a modestly differentiated interior to more advanced evolution with a dry silicate core, a hydrated silicate mantle, and a volatile‐rich crust. Here we compute the mass and hydrostatic flattening from more than one hundred billion three‐layer density models for Ceres and describe the characteristics of the population of density structures that are consistent with the Dawn observations. We show that the mass and hydrostatic flattening constraints from Ceres indicate the presence of a high‐density core with greater than a 1σ probability, but provide little constraint on the density, allowing for core compositions that range from hydrous and/or anhydrous silicates to a mixture of metal and silicates. The crustal densities are consistent with surface observations of salts, water ice, carbonates, and ammoniated clays, which indicate hydrothermal alteration, partial fractionation, and the possible settling of heavy sulfide and metallic particles, which provide a potential process for increasing mass with depth.  相似文献   

Harbour porpoise (Phocoena phocoena) conservation management: A dimensional approach     

Rhian E. Jenkins  Raymond D.H. Brown  Michael R. Phillips   《Marine Policy》2009,33(5):744-749

Harbour porpoises Phocoena phocoena are protected under the Habitats and Species Directive (92/43/EEC) and listed as a priority species in the City and County of Swansea's Biodiversity Action Plan (BAP). Increased coastal pressures demand better governance and this study adopted a dimensional analysis to produce a local management framework for harbour porpoise populations. Having established basic behavioural dynamics and identified critical habitats, a coastal zone use model was developed. This highlighted porpoise and coastal user interaction from a species perspective. Evidence was determined from observations and published research, and an Environmental Risk Assessment (ERA) was undertaken. An estimation of consequence probability was determined and revealed that continued coastal use, without mitigation, is likely to have significant local impacts on porpoise populations. A strengths, weaknesses, opportunities and threats (SWOT) analysis and legislative appraisal highlighted potential opportunities and deficiencies. Mitigation refers principally to industry, fisheries and recreation and suggestions include flexible zoning; speed and vessel restrictions; engineering solutions to noise intrusion and fisheries monitoring. A mixture of formal and informal regulations is recommended, together with educational projects and industry-funded research opportunities.  相似文献