by neufer » Tue Nov 22, 2016 3:25 pm
https://en.wikipedia.org/wiki/Sputnik_Planitia wrote:
<<Sputnik Planitia may have originated as an impact basin that subsequently collected volatile ices. Alternatively, it has been suggested that the accumulation of ices in this location depressed the surface there, leading to formation of a basin via a positive feedback process without an impact.
The accumulation of several kilometers of nitrogen ice in the basin may have resulted from the positive temperature gradient of Pluto's atmosphere, which would make a topographic depression a cold trap.
A high seasonal thermal inertia of Pluto's surface is an important driver of deposition of nitrogen ice at low latitudes, which receive less annual insolation than Pluto's polar regions due to its high obliquity.
The accumulation of ice would likely then have made Sputnik Planitia a positive gravity anomaly, which could have caused polar wander, reorienting the spin axis of Pluto to put the planitia near the Pluto-Charon tidal axis (the minimum-energy configuration). Sputnik Planitia is presently close to the anti-Charon point on Pluto, a result that has less than a 10% probability of arising by chance.>>
https://en.wikipedia.org/wiki/Moon wrote:
<<The concentration of maria on the Near Side likely reflects the substantially thicker crust of the highlands of the Far Side, which may have formed in a slow-velocity impact of a second moon of Earth a few tens of millions of years after their formation.
The far side of the lunar surface is on average about 1.9 km higher than that of the near side. Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side, compared with 2% of the far side. 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. 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.
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 due to the greater concentration of radioactive elements. Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside Lowell crater, 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=" https://en.wikipedia.org/wiki/Sputnik_Planitia"]
<<Sputnik Planitia may have originated as an impact basin that subsequently collected volatile ices. Alternatively, it has been suggested that the accumulation of ices in this location depressed the surface there, leading to formation of a basin via a positive feedback process without an impact.
The accumulation of several kilometers of nitrogen ice in the basin may have resulted from the positive temperature gradient of Pluto's atmosphere, which would make a topographic depression a cold trap.
A high seasonal thermal inertia of Pluto's surface is an important driver of deposition of nitrogen ice at low latitudes, which receive less annual insolation than Pluto's polar regions due to its high obliquity. [b][color=#0000FF][u]The accumulation of ice[/u] would likely then have made Sputnik Planitia a positive gravity anomaly, which could have caused polar wander, reorienting the spin axis of Pluto to put the planitia near the Pluto-Charon tidal axis (the minimum-energy configuration). [u]Sputnik Planitia is presently close to the anti-Charon point on Pluto[/u], a result that has less than a 10% probability of arising by chance.[/color][/b]>>[/quote][quote=" https://en.wikipedia.org/wiki/Moon"]
<<The concentration of maria on the Near Side likely reflects the substantially thicker crust of the highlands of the Far Side, which may have formed in a slow-velocity impact of a second moon of Earth a few tens of millions of years after their formation. [b][color=#0000FF]The far side of the lunar surface is on average about [u]1.9 km higher[/u] than that of the near side.[/color][/b] Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side, compared with 2% of the far side. 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. 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.
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 due to the greater concentration of radioactive elements. Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside Lowell crater, 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]