The maximum excavation depths of the Birkeland and De … Use the link below to share a full-text version of this article with your friends and colleagues. Journal of Geomagnetism and Aeronomy, Nonlinear The thickness distribution of ejecta is derived from the measured thicknesses of ejecta deposits using an updated ballistic sedimentation model. [10] In our second model, radioactive element abundance within the ejecta layer does not decrease with depth, assuming that the exponential decrease used in our first model is not necessarily the only possible concentration function. The term ‘lava’ is also used for the solidified rock formed by the cooling of a molten lava flow. We find that crustal-thickness differences of 21 km (mean = 65 km, minimum = 50 km, maximum = 71 km) can be generated for e = 0.02, a = 20 RE, Tb = 1175°C, and qo = 27 mW/m2 (Fig. Oceanography, Interplanetary Clarifying the thickness distribution of impact ejecta gives insights into the process of impact cratering, the stratigraphy of planetary crust, future sampling site selection, and the source of lunar samples. Using the factory edge as a guide, trim off 6mm along the length (Figure 1). Difference in lunar heat flow between Apollo 15 and Apollo 17 landing sites caused by a Th‐enriched layer whose thickness depends on the distance from the postulated Imbrium impact. An exponential decrease of Th with depth based on the LP‐GRS surface concentrations and ejecta layer thicknesses estimated from the postulated Imbrium impact can explain the difference in heat flow between the two Apollo measurements. As for the possible location of the PKT, one can take the locations of the dipole axes of global elemental distributions as given by Feldman et al. optically thick ejecta at those early epochs. Thorium concentration is assumed to be constant. This data can be used to estimate the volume of ejecta. Ganymede has large, bright regions of ridges and grooves that slice across older, darker terrains. We further vary Housen et al. Geophysics, Geomagnetism Pike EPSL 23 (1974) EJECTA FROM LARGE CRATERS ON … and you may need to create a new Wiley Online Library account. Of course, given the rapid decrease of deposit thickness with distance, these numbers are highly sensitive to impact location and transient crater size. An ejecta blanket is a generally symmetrical apron of ejecta that surrounds an impact crater; it is layered thickly at the crater's rim and thin to discontinuous at the blanket's outer edge. When an impacting asteroid and/or comet hits that crust, it produces enormously high shock pressures. With only two data points, one can of course speculate, but we prefer to postpone any quantitative investigation of these effects. These thicknesses are quantitatively similar to those measured in Thoroddsen (Reference Thoroddsen 2002), but the ejecta thickness cannot be measured in the current experiments. The average ejecta thickness is greatest at the transient crater rim and decreases as one over the distance from the rim cubed. Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username. In addition, the penetration depth of the Schrödinger impact is too shallow to penetrate through the lunar crust. Maximum ejecta thickness is ~800 m at the rim, that decreases to <30 m within 35% of the maximum ejecta range. Our results underline the need for further, if possible global, coverage of lunar surface heat flow. Another explanation is given by Wieczorek and Phillips [2000], who pointed out that the difference between the two Apollo measurements could be explained by the Apollo 15 landing site being closer to the center of the high‐Th PKT. We recognize that Yutu‐2 is exploring along the shared wall of two secondaries from Finsen, and subsurface materials are older than Finsen. Geology and Geophysics, Physical In a simple study we show that lunar heat flow is contingent upon the thickness of the ejecta blanket of the hypothetical impact. proximal ejecta of these craters varies only with regolith thickness and crater size since they are all very young.
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