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Race Jackson Wrote:
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> There are several so called lunar mysteries of
> earth's moon - but most of them turn out to be
> based on false claims or are actually not really
> that mysterious. But there is one that is not
> explained.
>
> The currently accepted view of the moon's
> formation is that a mars sized planet plowed into
> the earth very early on, and a bunch of material
> was ejected from the collision into lunar orbit.
> Because much of the dense minerals of the earth
> were already headed to the core, the ejecta was
> lighter crustal material. So good so far.
>
> Now the lunar orbit after collision was much
> closer to the earth than the current orbit (it was
> then about 20K kilometers away). Both bodies were
> blazingly hot and molten. The moon aggregated all
> the ejecta to become the size that it is today,
> and became fairly quickly tidally locked because
> the orbit was so close (the closer two orbiting
> bodies are, the more quickly the smaller one gets
> tidally locked).
>
> The tidal locking explains why the crust on the
> side of the moon facing the earth is much thinner
> than the crust on the far side. Because they were
> so hot, the moon was venting lots of gas. Because
> the earth was so hot, the near side of the moon
> was hotter than the far side, so the gases
> solidified on the far side. The deposition of hot
> gases thus made the far side of the moon's crust
> thicker than the near side of the moon's crust.
> Again, no mystery.
>
> However. The near side of the moon has most of the
> mascons (high gravity areas). The moon (and the
> earth) were bombarded by lots of asteroids. The
> biggest asteroids that hit the moon penetrated the
> thinner lunar crust side permitting heavier molten
> material to flow up and out, thus making mascons -
> whereas on the thicker crust side they didn't
> penetrate the crust, thus did not permit heavier
> molten material to flow up and out. The "mares" on
> the moon are all on the side facing the earth (the
> thinner crust side), and the mares correspond
> quite well to the mascons. Again, perfectly
> reasonable.
>
> (Interesting side tidbit - it is because of the
> lunar mascons that it is hard to keep anything in
> orbit around the moon for more than a couple
> years. The mascons mess with lunar orbits and thus
> bring lunar orbiters crashing down into the moon
> unless whatever orbits is regularly making
> adjustments - which means firing retro rockets,
> which means any long term lunar orbiter has to
> carry a bunch of fuel just to keep in orbit.)
>
> Here's the mystery. The big bombardment happened
> around 4 billion years ago - when the moon orbited
> only around 30K kilometers away from the earth,
> unlike today when it orbits an average of 240K
> kilometers away. The earth shielded the near side
> of the moon from asteroid strikes (because it was
> so close to the earth). Since the moon was already
> tidally locked to the earth, how did big asteroids
> manage to hit the near side of the moon, since
> these asteroid strikes occurred when the moon was
> much closer to the earth?


Race, I've just come across this article on new findings from the LRO, which you may find interesting:

This spinning moon shows where debris from giant impacts fell

Quote

Astronomers originally assumed that the light plains were ancient lava flows from volcanoes. But rocks brought back from one of these plains by Apollo 16 astronauts in 1972 did not have volcanic compositions. That finding led some scientists to suspect the plains, which cover about 9.5 percent of the lunar surface, came from giant impacts.

Meyer’s map supports the impact idea. Most of the plains, which are visible across the whole moon, seem to originate from debris spewed from the Orientale basin, a 930-kilometer-wide bowl in the moon’s southern hemisphere that formed about 3.8 billion years ago.

“It looks like there’s just a giant splat mark,” Meyer says. About 70 percent of the lunar plains come from either Orientale or one other similar basin, she reported March 22 at the Lunar and Planetary Science Conference. “What this is telling us,” she says, “is these large basins modified the entire lunar surface at some point.”

Carol

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Subject Views Written By Posted
A true lunar mystery 966 Race Jackson 29-Mar-18 23:53
Re: A true lunar mystery 236 carolb 30-Mar-18 00:33
Re: A true lunar mystery 228 Spiros 30-Mar-18 12:31
Re: A true lunar mystery 184 Race Jackson 30-Mar-18 16:14
Re: A true lunar mystery 212 D-Archer 30-Mar-18 13:35
Re: A true lunar mystery 248 carolb 30-Mar-18 16:22
Re: A true lunar mystery 206 carolb 02-Apr-18 17:34
Re: A true lunar mystery 362 Itatw70s 03-Apr-18 16:25


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