Despinning plus global contraction and the orientation of lobate scarps on Mercury: Predictions for MESSENGER

Observations by the Mariner 10 spacecraft suggest that the lobate scarps on Mercury, which have been interpreted to record at most 1-2 km of radial contraction of the planet after the end of the Late Heavy Bombardment, possess a global, preferred N-S orientation but lack a strong latitudinal dependence on their surface expression. Here, we reexamine the idea that a decrease in the planetary rotation rate (despinning) coupled with global contraction of at least 3-5.5 km prior to the end of Late Heavy Bombardment resulted in global N-S oriented thrust faults. The surface expression of these faults is assumed to have been erased by the end of the Late Heavy Bombardment, and the faults were subsequently reactivated by later global contraction, producing generally N-S oriented thrust faults from an isotropic stress field. We use the estimate of >3-5.5 km contraction prior to ∼4 Ga as an additional constraint to thermomechanical simulations of the evolution of Mercury, finding that a wide range of models are consistent with this observation. The fact that a wide range of states are consistent with the contraction of Mercury prior to the end of Late Heavy Bombardment but only a restricted set of states are consistent with the at most 1-2 km of subsequent contraction bolsters the idea that there may be hidden strain on Mercury, features unseen by Mariner 10 but likely visible to the MESSENGER spacecraft.     

Photometric catalogues: Present and future

Current sources of stellar photometric data are described, together with a summary of the quality of such data. The main future problem is the adequate dissemination of the information collected.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978.     

Benchmarking the first decade of post-apartheid fisheries reform in South Africa

The paper uses the three legislative criteria of resource sustainability, economic stability and social equity to measure the past decade of fisheries reform in South Africa. All three components of the reform process have been successful, although this judgement is subject to a number of important qualifications. First, the data available to measure success are limited. Second, both sustainability and stability are vulnerable to volatile factors external to the reform process (particularly variability in recruitment, climate change and exchange rate fluctuations) capable of derailing the process. Substantial alteration of the fishing industry by internal transformation of existing companies and the reallocation of access rights to new black entrants has led to a composition that closely reflects that of society as a whole and therefore meets the goal of equity. In the process, however, bona fide traditional fishers with a historical dependence on fishing have largely been denied legitimate access to the fisheries, and meeting their aspirations remains a challenge.