Nature<\/a>, the paper also provides a snapshot of the moon\u2019s tumultuous past that could help explain longstanding puzzles such as why the moon\u2019s crater-riddled far side is so dramatically different from its smooth near side, which provided the backdrop for the Apollo moon landings in the 1960s and 1970s.<\/p>\nRoughly 4.3 billion years ago, when the solar system was still in its infancy, a giant asteroid slammed into the far side of the moon, blasting an enormous crater referred to as the South Pole-Aitken basin, or SPA. This impact feature is the largest crater on the moon, spanning more than 1,200 miles north to south, and 1,000 miles east to west. The oblong shape of the basin is the result of a glancing blow rather than a head-on impact.<\/p>\n
By comparing the shape of SPA to other giant impact basins across the solar system, Andrews-Hanna and his team found that these features get narrower in the down-range direction, with a shape resembling a teardrop or an avocado. Upending conventional wisdom that SPA was formed by an asteroid coming in from a southern direction, the new analysis reveals that SPA\u2019s shape narrows toward the south, indicating an impact coming from the north instead. The down-range end of the basin should be covered by a thick layer of material excavated from the lunar interior by the impact, while the up-range end should not, Andrews-Hanna explained.<\/p>\n
\u201cThis means that the Artemis missions will be landing on the down-range rim of the basin\u2014the best place to study the largest and oldest impact basin on the moon, where most of the ejecta, material from deep within the moon\u2019s interior, should be piled up,\u201d says Jeffrey Andrews-Hanna, a planetary scientist at the University of Arizona.<\/p>\n
In the paper, the group presents additional evidence supporting a southward impact from analyses of the topography, the thickness of the crust, and the surface composition. In addition, the results offer new clues about on the interior structure of the moon and its evolution through time, according to the authors.<\/p>\n
It has long been thought that the early moon was melted by the energy released during its formation, creating a magma ocean covering the entire moon. As that magma ocean crystallized, heavy minerals sunk to make the lunar mantle, while light minerals floated to make the crust. However, some elements were excluded from the solid mantle and crust and instead became concentrated in the final liquids of the magma ocean. Those \u201cleftover\u201d elements included potassium, rare earth elements, and phosphorus, collectively referred to as \u201cKREEP \u201c\u2014the acronym\u2019s first letter reflecting potassium\u2019s symbol in the periodic table of elements, \u201cK.\u201d According to Andrews-Hanna these elements were found to be particularly abundant on the moon\u2019s near side.<\/p>\n
\u201cIf you\u2019ve ever left a can of soda in the freezer, you may have noticed that as the water becomes solid, the high fructose corn syrup resists freezing until the very end and instead becomes concentrated in the last bits of liquid,\u201d he says. \u201cWe think something similar happened on the moon with KREEP.\u201d<\/p>\n
As it cooled over many millions of years, the magma ocean gradually solidified into crust and mantle. \u201cAnd eventually you get to this point where you just have that tiny bit of liquid left sandwiched between the mantle and the crust, and that\u2019s this KREEP-rich material,\u201d he says.<\/p>\n
\u201cAll of the KREEP-rich material and heat-producing elements somehow became concentrated on the moon\u2019s near side, causing it to heat up and leading to intense volcanism that formed the dark volcanic plains that make for the familiar sight of the \u201cface\u201d of the Moon from Earth, according to Andrews-Hanna. However, the reason why the KREEP-rich material ended up on the nearside, and how that material evolved over time, has been a mystery.<\/p>\n
The moon\u2019s crust is much thicker on its far side than on its near side facing the Earth, an asymmetry that has scientists puzzled to this day. This asymmetry has affected all aspects of the moon\u2019s evolution, including the latest stages of the magma ocean, Andrews-Hanna says.<\/p>\n
\u201cOur theory is that as the crust thickened on the far side, the magma ocean below was squeezed out to the sides, like toothpaste being squeezed out of a tube, until most of it ended up on the near side,\u201d he says.<\/p>\n
The new study of the SPA impact crater revealed a striking and unexpected asymmetry around the basin that supports exactly that scenario: The ejecta blanket on its western side is rich in radioactive thorium, but not in its eastern flank. This suggests that the gash left by the impact created a window through the moon\u2019s skin right at the boundary separating the crust underlain by the last remnants of the KREEP-enriched magma ocean from the \u201cregular\u201d crust.<\/p>\n
\u201cOur study shows that the distribution and composition of these materials match the predictions that we get by modeling the latest stages of the evolution of the magma ocean,\u201d Andrews-Hanna says.<\/p>\n
\u201cThe last dregs of the lunar magma ocean ended up on the near side, where we see the highest concentrations of radioactive elements. But at some earlier time, a thin and patchy layer of magma ocean would have existed below parts of the far side, explaining the radioactive ejecta on one side of the SPA impact basin.\u201d<\/p>\n
Many mysteries surrounding the moon\u2019s earliest history still remain, and once astronauts bring samples back to Earth, researchers hope to find more pieces to the puzzle. Remote sensing data collected by orbiting spacecraft like those used for this study provide researchers with a basic idea of the composition of the moon\u2019s surface, according to Andrews-Hanna. Thorium, an important element in KREEP-rich material, is easy to spot, but getting a more detailed analysis of the composition is a heavier lift.<\/p>\n
\u201cThose samples will be analyzed by scientists around the world, including here at the University of Arizona, where we have state -of-the-art facilities that are specially designed for those types of analyses,\u201d he says.<\/p>\n
\u201cWith Artemis, we\u2019ll have samples to study here on Earth, and we will know exactly what they are,\u201d he says. \u201cOur study shows that these samples may reveal even more about the early evolution of the moon than had been thought.\u201d<\/p>\n
Source: University of Arizona<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"Share this Article You are free to share this article under the Attribution 4.0 International license. When astronauts…\n","protected":false},"author":2,"featured_media":119367,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[85,46,8245,141],"class_list":["post-119366","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-il","tag-israel","tag-moon","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/119366","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=119366"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/119366\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/119367"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=119366"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=119366"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=119366"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}