by johnnydeep » Sun Jul 19, 2020 3:22 pm
BDanielMayfield wrote: ↑Sun Jul 19, 2020 12:35 pm
RocketRon wrote: ↑Sun Jul 19, 2020 4:50 am
Are there any good proposed explanations why these 'lava seas' are all on 'our' side of the Moon ?
In the latest thinking, is this thought to be an artifact of the moons formation, or subsequent to that ?
wikipedia < moon wrote:The dark and relatively featureless lunar plains, clearly seen with the naked eye, are called maria (Latin for "seas"; singular mare), as they were once believed to be filled with water;[69] they are now known to be vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.[70] The majority of these lavas erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side "maria".[71]
Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side,[72] compared with 2% of the far side.[73] This is thought to be due to a concentration of heat-producing elements under the crust on the near side, seen on geochemical maps obtained by Lunar Prospector's gamma-ray spectrometer, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.
Sorry, I cut the quote off to soon to answer Ron's 2nd question. Continuing...
Most of the Moon's mare basalts erupted during the Imbrian period, 3.0–3.5 billion years ago, although some radiometrically dated samples are as old as 4.2 billion years.[76] Until recently, the youngest eruptions, dated by crater counting, appeared to have been only 1.2 billion years ago.[77] In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.[78] Moonquakes and releases of gas also indicate some continued lunar activity.[78] In 2014 NASA announced "widespread evidence of young lunar volcanism" at 70 irregular mare patches identified by the Lunar Reconnaissance Orbiter, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements.[79][80][81][82] Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside the crater Lowell,[83][84] Orientale basin, located in the transition zone between the near and far sides of the Moon. An initially hotter mantle and/or local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities also on the far side in the Orientale basin.
Hmm. Still nothing explicit there about just
why the mares are on the near side. An "obvious" explanation I immediately thought of for why the mares are mostly on the near side is that the near side is simply heavier! That is, there are more heavy elements on or under the near side, with the result that that side ends up being the one tidally locked with the earth. Any evidence for this? Probably not since most immediately obvious explanations turn out to be wrong...
Unless we are supposed to draw this conclusion based on the statement that the "concentration of heat-producing elements under the crust on the near side" is the cause. Since the heat producing elements would be the heavier ones?
[quote=BDanielMayfield post_id=304297 time=1595162151 user_id=139536]
[quote=RocketRon post_id=304289 time=1595134218]
Are there any good proposed explanations why these 'lava seas' are all on 'our' side of the Moon ?
In the latest thinking, is this thought to be an artifact of the moons formation, or subsequent to that ?
[/quote]
[quote="wikipedia < moon"]The dark and relatively featureless lunar plains, clearly seen with the naked eye, are called maria (Latin for "seas"; singular mare), as they were once believed to be filled with water;[69] they are now known to be vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.[70] The majority of these lavas erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side "maria".[71]
Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side,[72] compared with 2% of the far side.[73] This is thought to be due to a concentration of heat-producing elements under the crust on the near side, seen on geochemical maps obtained by Lunar Prospector's gamma-ray spectrometer, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.[/quote]
Sorry, I cut the quote off to soon to answer Ron's 2nd question. Continuing...
[quote]Most of the Moon's mare basalts erupted during the Imbrian period, 3.0–3.5 billion years ago, although some radiometrically dated samples are as old as 4.2 billion years.[76] Until recently, the youngest eruptions, dated by crater counting, appeared to have been only 1.2 billion years ago.[77] In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.[78] Moonquakes and releases of gas also indicate some continued lunar activity.[78] In 2014 NASA announced "widespread evidence of young lunar volcanism" at 70 irregular mare patches identified by the Lunar Reconnaissance Orbiter, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements.[79][80][81][82] Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside the crater Lowell,[83][84] Orientale basin, located in the transition zone between the near and far sides of the Moon. An initially hotter mantle and/or local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities also on the far side in the Orientale basin.[/quote]
[/quote]
Hmm. Still nothing explicit there about just [i]why [/i]the mares are on the near side. An "obvious" explanation I immediately thought of for why the mares are mostly on the near side is that the near side is simply heavier! That is, there are more heavy elements on or under the near side, with the result that that side ends up being the one tidally locked with the earth. Any evidence for this? Probably not since most immediately obvious explanations turn out to be wrong... :ssmile: Unless we are supposed to draw this conclusion based on the statement that the "concentration of heat-producing elements under the crust on the near side" is the cause. Since the heat producing elements would be the heavier ones?