Difference between revisions of "December 9, 2011"
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=Noticing What is Missing= | =Noticing What is Missing= | ||
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<em>image by [mailto:Yurkevich5555@yandex.ru Юркевич Сергей] (Sergey Yurkevich), Petrozavodsk, Russia</em><br /> | <em>image by [mailto:Yurkevich5555@yandex.ru Юркевич Сергей] (Sergey Yurkevich), Petrozavodsk, Russia</em><br /> | ||
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| − | Sergey's image captures much of the nearside's heavily cratered terrain. There are two types of surface here. | + | Sergey's image captures much of the nearside's heavily cratered terrain. There are two types of surface here. |
| − | Craters on top of craters characterize the landscape near the terminator, but further east (in the area near the | + | Craters on top of craters characterize the landscape near the terminator, but further east (in the area near the |
| − | bottom center) there are fewer craters with smooth plains in between. In general, the lunar highlands are the | + | bottom center) there are fewer craters with smooth plains in between. In general, the lunar highlands are the |
| − | oldest rocks on the Moon and may be the remnants of the low density anorthositic scum that floated to the top | + | oldest rocks on the Moon and may be the remnants of the low density anorthositic scum that floated to the top |
| − | of the lunar magma ocean. If this was so, the surface should be saturated with craters that date from the final | + | of the lunar magma ocean. If this was so, the surface should be saturated with craters that date from the final |
| − | days of the accretionary bombardment that built the Moon. That is true for the heavily cratered areas such as | + | days of the accretionary bombardment that built the Moon. That is true for the heavily cratered areas such as |
| − | near the terminator, but the places where smooth plains are widespread are not saturated. I have thought that | + | near the terminator, but the places where smooth plains are widespread are not saturated. I have thought that |
| − | the plains materials could be volcanic, resurfacing the original anorthositic crust and destroying the impact | + | the plains materials could be volcanic, resurfacing the original anorthositic crust and destroying the impact |
| − | craters. But there is little good evidence for volcansim in the highlands. There is evidence that ejecta from the | + | craters. But there is little good evidence for volcansim in the highlands. There is evidence that ejecta from the |
| − | Orientale impact veneer parts of the area shown here. But it doesn't seem like that ejecta would be thick enough | + | Orientale impact veneer parts of the area shown here. But it doesn't seem like that ejecta would be thick enough |
| − | to explain the sparcity of craters in the smooth plains zones. So there is no good explanation for the origin of the | + | to explain the sparcity of craters in the smooth plains zones. So there is no good explanation for the origin of the |
| − | smooth plains, nor for the missing ancient craters. <br /> | + | smooth plains, nor for the missing ancient craters. |
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<em>[mailto:tychocrater@yahoo.com Chuck Wood]</em><br /> | <em>[mailto:tychocrater@yahoo.com Chuck Wood]</em><br /> | ||
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| + | <p><b>Yesterday's LPOD:</b> [[December 8, 2011|Circling Treasures]] </p> | ||
| + | <p><b>Tomorrow's LPOD:</b> [[December 10, 2011|Escape!]] </p> | ||
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Latest revision as of 15:18, 1 March 2015
Noticing What is Missing
image by Юркевич Сергей (Sergey Yurkevich), Petrozavodsk, Russia
Sergey's image captures much of the nearside's heavily cratered terrain. There are two types of surface here.
Craters on top of craters characterize the landscape near the terminator, but further east (in the area near the
bottom center) there are fewer craters with smooth plains in between. In general, the lunar highlands are the
oldest rocks on the Moon and may be the remnants of the low density anorthositic scum that floated to the top
of the lunar magma ocean. If this was so, the surface should be saturated with craters that date from the final
days of the accretionary bombardment that built the Moon. That is true for the heavily cratered areas such as
near the terminator, but the places where smooth plains are widespread are not saturated. I have thought that
the plains materials could be volcanic, resurfacing the original anorthositic crust and destroying the impact
craters. But there is little good evidence for volcansim in the highlands. There is evidence that ejecta from the
Orientale impact veneer parts of the area shown here. But it doesn't seem like that ejecta would be thick enough
to explain the sparcity of craters in the smooth plains zones. So there is no good explanation for the origin of the
smooth plains, nor for the missing ancient craters.
Chuck Wood
Yesterday's LPOD: Circling Treasures
Tomorrow's LPOD: Escape!
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