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Mars Magnetic Mystery and Active Tectonics on Venus

发布时间:2019-03-29 09:03来源:未知 责任编辑:于莹

报告题目:Mars Magnetic Mystery and Active Tectonics on Venus

报 告 人:Donna Jurdy

报告时间:2019年04月04日 09时30分

报告地点:天文楼212报告厅

报告人:Donna Jurdy 教授 (美国西北大学地球与行星科学系,黎健邀请)
  目:Mars Magnetic Mystery and Active Tectonics on Venus
  间:4月4日上午9:30(因报告内容较多,报告时间为1个半小时)
  点:天文楼212报告厅
  要: Mars has long fascinated humans. Early known as a wandering heavenly body, it played the central role in the development of the laws of planetary motions. When telescopes revealed earth-like polar caps and patterns interpreted as canals, intelligent beings on the Red Planet were expected. Mars held more surprises: Years later NASA missions with high resolution orbiting cameras as well as surface rovers showed that water recently flowed on the surface. Serendipity with the MGS mission resulted in the unexpected discovery of a strongly magnetized crust. Mars does not currently have a magnetic field; its remanent magnetism remains from its distant past. We have studied the most strongly magnetized region, the southern hemisphere within 40 degrees of 40S, 180. With MGS satellite mapping data at ~400 km extrapolated downward to the surface, sources are modeled with monopoles. Over this region, nearly an octant of Mars, about a dozen monopoles can account for >94% of the variance of the surface magnetization. In models positive monopoles dominate, with the strongest surface magnetization often adjacent to ancient multi-ringed basins.  Depth estimates through two approaches suggest that martian magnetization exceeds 100 km.
   Mars' interior remains largely unknown.  NASA's ongoing InSight mission ranks as the first dedicated to study the Martian interior, with a seismometer, heatflow probe and magnetometer.  This mission could establish the current temperature regime and crust and mantle structure, even the size and state of Mars' core.
 
   Venus' surface hosts less than 1000 impact craters, suggesting its age less than 600 m.y. In addition, hundreds of circular to elongate features, ranging from 60 to 2600 km, and averaging somewhat over 200 km, in diameter, scatter on its surface.  These enigmatic structures have been termed "coronae" and attributed to either tectono-volcanic or impact-related mechanisms. Quantitative analysis of symmetry and topography applied to coronae and similarly-sized craters allows assessment of the hypothesized impact origin of these features. Based on the morphology and global distribution of coronae, as well as crater density within and near coronae, the impact origin for most coronae is rejected.  The high level of modification of craters within coronae further supports their tectonic nature. The relatively young Beta-Atla-Thema region region shws a high corona concentration closely associated with the chasmata system, suggesting a tectonic origin of both. A quantitative comparison of topography for Venus’ features with Earth's for similarities and differences may provide clues to the dynamics features. To do this, topographic profiles across a set of features are used to determine average profiles for each.  Then averages are correlated to establish the degree of similarity.  From this correlation a covariance matrix is constructed, diagonalized for eigenvalues, or principal components. These can be displayed as profiles. Correlations and principal components allow assessment of the degree of similarity and variability of the shapes of the average profiles. These analyses thus offer independent and objective modes of comparison. For example, comparing terrestrial mid-ocean ridges, some Venus chasmata most closely resemble the ultra-slow Arctic spreading center.
   Proposed future missions to Venus would answer some remaining questions. These planned missions will be outlined.
报告人简介: Donna Jurdy, currently a professor at the Department of Earth & Planetary Sciences, Northwestern University, received her PhD degree in the University of Michigan. She spent several years at Princeton University as a Research Geophysicist.  A Fellow of the Geological Society of America, she is also a member of the American Geophysical Union, the Society of Exploration Geophysicists and the Association for Women Geoscientists. Her current interests are tectonics of Venus, the magnetic lineations on Mars, and Titan's surface, and also Ganymede and the volcanism of Io.


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