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- Title
Impact Generation of Holes in the Early Lunar Crust: Scaling Relations.
- Authors
Jackson, Alan P.; Perera, Viranga; Gabriel, Travis S. J.
- Abstract
After its formation, the Moon is widely believed to have possessed a deep, global magma ocean. As it cooled, an anorthositic crust formed, floating atop this magma ocean and acting as an insulating blanket. As well as forming the Moon, the Moon‐forming giant impact also released more than a lunar mass of debris into heliocentric orbit. Reimpacting debris subjected the newly formed Moon to an extremely intense bombardment. We have conducted a suite of impact simulations for a range of conditions representative of this early period. We find that impact outcomes can be divided into four regimes and construct scaling relations for the transitions between these regimes and size of impact features. Exposure of liquid magma to the surface is generally more efficient than previously assumed, implying significant shortening of the solidification time of the Lunar Magma Ocean. Comparison with work on icy satellites also suggests that penetration of a solid crust overlying liquid is a relatively universal process with weak dependence on target material properties. Plain Language Summary: The Moon is believed to have formed in a giant impact between Earth and another planet‐sized body. After formation, the Moon was very hot and likely had a deep layer of magma. As the magma cooled and solidified, some of the solid minerals floated to the surface, creating an insulating blanket. As well as forming the Moon, the giant impact released over a Moon's mass of debris into orbit around the Sun, some of which returned to hit the young Moon. We ran computer simulations to understand what happens to the solid crust when debris hits it. We find that these impacts can be divided into four types and developed equations relating the size of the scar produced to impact energy and crust thickness. Creating a hole in the crust makes it a less effective insulating blanket, allowing heat out faster. We find that impacts more easily produce holes than previously assumed, so the magma should have cooled faster. Icy satellites are similar in structure having a solid ice layer with water underneath, and comparing with previous work, we suggest that how easy it is to puncture the solid layer does not depend much on what it is made out of. Key Points: Impacts into crusts overlying magma can be divided into four outcomes ranging from classical crater‐forming to complete penetrationWe derived impact energy scaling relations for the transitions between regimes and size of impact featuresPenetration of the early lunar crust would have been extensive—reimpacting debris substantially decreased magma ocean solidification time
- Subjects
LUNAR craters; HARD rock minerals; LIQUID surfaces; MAGMAS; ORBITS (Astronomy); MOON
- Publication
Journal of Geophysical Research. Planets, 2023, Vol 128, Issue 4, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2022JE007498