Ancient impact that formed Earth's moon was likely a one-two punch

rod

Oct 22, 2019
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"lead author Erik Asphaug" My observation, a busy writer and NASA ADS Abstract service shows this :)

The collision chains model for Earth and Venus is reported at this site too. Earth and Venus grew up as rambunctious planets, https://phys.org/news/2021-09-earth-venus-grew-rambunctious-planets.html
"What doesn't stick comes around: Using machine learning and simulations of giant impacts, researchers at the Lunar and Planetary Laboratory found that the planets residing in the inner solar systems were likely born from repeated hit-and-run collisions, challenging conventional models of planet formation. Planet formation—the process by which neat, round, distinct planets form from a roiling, swirling cloud of rugged asteroids and mini planets—was likely even messier and more complicated than most scientists would care to admit, according to new research led by researchers at the University of Arizona Lunar and Planetary Laboratory."

Indeed, a very messy work to make the solar system now using the solar nebula and spinning, protoplanetary disk said to create all we see today in the ecliptic :) Concerning the Moon forming impacts now, much is going on in the simulations. My observation. It looks like this model needs two giant impacts now to make the Moon, not just one impact using Theia as the impactor. There remains the question for me as to how much gas and dust mass is used in the model for the region between 0.7 au out to 1.0 au as well. Erik Asphaug is published on the multiple giant impacts model to make the Moon. Moon Formation in Three Acts, https://ui.adsabs.harvard.edu/abs/2020EPSC...14..485A/abstract, September 2020. "Overview. Terrestrial planets grew in a complex series of late stage giant impacts, and Moon-formation was among last to occur around Earth. But was it a singular event? Here we propose it was three or more episodes involving two bodies and the Sun, an almost-merger followed by an interlude, followed by a merger...To address the major deficiencies of the standard model while preserving its major strengths, we have developed a theoretical basis for a collision chain origin of the Moon. We show it to be a common pathway of planet formation, slowing the random velocities until merger is probable. There are innumerable pathways so it is premature to hone in on one scenario. A scenario meriting further research is an ~0.2 MEarth planet that become a mantle-stripped Theia, that then returns thousands to millions of years later for a merger on a strongly unaligned impact axis...To represent all possible collisions, we clone each SPH outcome into 1000 random orientations and evolve each clone, including the other major planets, until they have another collision with a planet, or for 50 Myr when most giant impact chains are finished."

There is plenty going on here with various impacts and time scales used. I still would like to see a proto-earth rock and Theia rock, perhaps from the 0.2 earth mass model on display. However, this is likely asking too much of the model at present :)
 
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May 14, 2021
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Makes sense. This was sorta like a roller derby, most of the stuff was going in more or less the same direction, slightly different speeds depending on orbit size, eccentricity, and inclination. Most of the stuff approaching Earth had somewhat slow speeds in the Earth frame of reference. With lots of gas and dust in the inner system larger objects would have slowly spiraled in toward the Sun. Earth crossers of the day, some would have hit, not just one, but many and various locations on the Earth, some just grazing it, dictating its final obliquity (the moon dictates Earth's rotational velocity). Some may have passed by on the sunward side close enough Earth altered its orbit to pass outward toward Mars (small target in a large orbit, hard to hit, Mars stays small), then Jupiter and the big guys would have handled them from there. Many would have spiraled in until it passes close by the outer side of Earth, and its orbit would be slightly altered until they may have become Venus approachers and crossers, Earth fed Venus until it became its 'sister planet'. One or more of the larger ones grazed on the sun side of Venus to cause retrograde rotation. What few got by Venus, if they became Mercury crossers, would have higher orbital velocities where they would hit Mercury hard knocking off the outer layers, giving it a larger core proportion, most got by and ended up in the Sun giving it more 'metals'. As the scientists play with the computer models, they will come closer to the story.
 
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rod

Oct 22, 2019
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Giant impacts are all the rage now in planet building scenarios. However, objects in the meter size and 300 meter size collisions, can hit at supersonic velocities in the models, large objects too. Many evaporation events follow. As Pogo noted in #5, "As the scientists play with the computer models, they will come closer to the story."

It is also likely the newer models will continue to place additional constraints on various impact events postulated to create the solar system and what we see today in the ecliptic (thus potentially more peculiar collisions required). More constraints could add additional problems *to the story* of origins told today, as investigations continue. This is becoming apparent now with increased observations showing more details in *young stars* with protoplanetary disks. Defining how much dust and gas mass there is around them is challenging and showing how tiny dust grains can grow into mature planets like we see at Mars, Earth, Venus, and Mercury, let alone the super-earths documented now around other stars.
 
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Catastrophe

"There never was a good war, or a bad peace."
I just Googled "how many comets in Oort Cloud?", and got this:

"It encloses the Solar System, with an outer edge that reaches almost a quarter of the way to the nearest star. By taking the size of the Oort cloud into account, and the number of long-period comets that have been seen, astronomers estimate that a staggering one 'trillion' (12 zeros) comets may be out there!"

On the one hand, I thought it was not actually established (as scientific fact) that the Oort Cloud existed, and on the other hand, it is thought *estimated) to contain 1,000,000,000,000 comets.

I mention this as there are supposed to be some pretty big comets out there, some possibly being diverted in our direction,.


Cat :)
 
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rod

Oct 22, 2019
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Cat, good observation in post #7. See this article and thread, Comets: Facts about the 'dirty snowballs' of space, https://forums.space.com/threads/comets-facts-about-the-dirty-snowballs-of-space.47657/

That thread reports some 3743 comets documented today, back in 1998, about 1009 documented. Allen's uses 10^11 to 10^13 comets in the postulated Oort cloud :) All of this requires a very messy, protoplanetary disk with large amount of dust and gas spinning around the proto-sun to make this cloud. Other models today explaining the origin of interstellar comets, indicate even large disk masses are needed, some perhaps more than 50% of the star's mass in the disk to create this stuff :)
 
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rod

Oct 22, 2019
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Rod, I am getting Page not found on that reference. Do I need membership to enter?

Cat :)

Try that. Looks like a duplicate report was posted on the topic.
 
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