A Statistical Analysis of Corona Topography: New Insights into Corona Formation and Evolution

Introduction: Extensive mapping of the surface of Venus and continued analysis of Magellan data have allowed a more comprehensive survey of coronae to be conducted [1]. Our updated corona database contains 514 features, an increase from the 326 coronae of the previous survey [2]. We include a new set of 106 Type 2 or 'stealth' [3] coronae, which have a topog-raphic rather than a fracture annulus [1, 3]. The large increase in the number of coronae over the 1992 survey results from several factors, including the use of the full Magellan data set and the addition of features identified as part of the systematic geologic mapping of Venus. Parameters of the population that we have analyzed to date include size and topography [1, 4]. Method. The updated corona database presents a unique opportunity to perform rigorous statistical analysis, as it contains a large amount of data that come from a well-defined population. Because the data are so voluminous and of such high quality, conclusions based on statistically significant results are definitive. Our initial analyses of the expanded corona population has already produced some new scientific results [4]. As an example of what can be learned from the dimensional information in the corona database , we performed a strict hypothesis test to determine if the Type 1 and Type 2 coronae widths are statistically 'the same'. Because both population widths have classic lognormal distributions, the hypothesis test was conducted on the geometric means for the two classes of coronae. The Type 1 coronae have a geometric mean diameter of 221.5 km with a corresponding 95% confidence interval of 209.8 – 233.9. The Type 2 coronae have a geometric mean of 208.2 km with a corresponding 95% confidence interval of 190.0 – 228.1 km [4]. The amount of overlap between the confidence intervals of the two populations indicates that the mean values cannot be distinguished statistically. We conclude that there is statistically no difference between the distributions of corona diameters, and we infer that the Type 1 and 2 coronae come from the same population [4]. The distribution of widths for the combined Type 1 and 2 coronae are strongly lognormal. The classic lognormal character suggests that the physical processes responsible for corona formation are operating over a limited scale, and that there might exist a continuous , but limited, range of subpopulations. It is these subpopulations that we hope to identify, …