Interesting points Torbjorn. Today we have more than 4200 exoplanets confirmed. UOE or unobservable event, how many giant impact events have been observed among the more than 4200 exoplanets that created moons orbiting them? My answer is none. The same applies to Theia. If Theia existed, it is clearly not observable today in the solar system and neither is the giant impact event with Theia. This is not a direct observation like Galileo used to argue against the geocentric astronomy with his telescope but interpretation using various modeling assumptions.
I think we agree on the generals, but maybe not on impacts. We can't see exomoons yet. But we know from our system as well as other systems that collisions are ubiquitous over cosmic time scales. Pluto-Charon is a fair copy of Earth-Moon, with the same impact history creating the smaller object.
Also, Theia has now been observed on the element level [ https://www.sciencealert.com/we-may-have-finally-found-a-chunk-of-theia-buried-deep-inside-the-moon
An aside: I just read something that you may be interested in, You have been discussing planetary disks, and unless I am mistaken how they seem depleted of material when we observe them.
I don't know if you have seen this yet, maybe there is a Space article I will get to later. It is a result from the first (they claim) integrated gravitation and magnetism effects on protoplanetary disks.
"With the aid of the "Piz Daint" supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano, these scientists have now simulated the development of the protoplanetary disk both under the influence of gravity and in the presence of a magnetic field, thereby discovering a completely new mechanism that could explain previously unexplained observations.
One such unexplained observation is that planets in our solar system today rotate much more slowly than the protoplanetary disk from which they must have once emerged. During the formation of planets, as well as of stars and black holes, enormous amounts of angular momentum must be lost, but how they lost this momentum has remained unclear. This so-called angular momentum problem is well-known in astrophysics. "Our new mechanism seems to be able to solve and explain this very general problem," says Mayer."
"The newly developed method led to surprising results concerning the interaction between GI and the magnetic field. It was shown that the spiral arms formed by gravity in the protoplanetary disk act like a dynamo, stretching and strengthening the magnetic seed. As a result, the magnetic field grows and gains strength. At the same time, this process generates much more heat in the protoplanetary disk than previously assumed. Most surprising for the researchers, however, was the fact that the dynamo seems to have a significant influence on the motion of the matter. The dynamo pushes it vigorously both inward, to accrete on the star, and outward, away from the disk. This means that the disk is evolving much faster than previous theories had suggested.
"The simulation shows that the energy generated by the interaction of the forming magnetic field with gravity acts outwards and drives a wind that throws matter out of the disk," Mayer says. This would cause 90 percent of the mass to be lost in less than a million years. "If this is true, this would be a desirable prediction, because many of the protoplanetary disks studied with telescopes that are a million years old have about 90 percent less mass than predicted by the simulations of disks formation so far," explains the astrophysicist."
; my bold.]
So their timescales fit, their angular momentum fits, and as a plus this may be a generic outcome as the fields looks vaguely analogous to the weak zonal fields that are dynamo generated in the interstellar gas of spiral galaxy disks.
But wait! There's more! From a 2014 paper I was reminded of:
"Now researchers at MIT, Cambridge University, and elsewhere have provided the first experimental evidence that our solar system's protoplanetary disk was shaped by an intense magnetic field that drove a massive amount of gas into the sun within just a few million years. The same magnetic field may have propelled dust grains along collision courses, eventually smashing them together to form the initial seeds of terrestrial planets."
"The researchers then measured the magnetic strength of each grain, and calculated the original magnetic field in which those grains were created. Based on their calculations, the group determined that the early solar system harbored a magnetic field as strong as 5 to 54 microteslas — up to 100,000 times stronger than what exists in interstellar space today. "
""Explaining the rapid timescale in which these disks evolve — in only a few million years — has always been a big mystery," says Roger Fu, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences. "It turns out that this magnetic field is strong enough to affect the motion of gas at a large scale, in a very significant way.""
"It's unlikely that chondrules formed via electric currents, or X-wind — flash-heating events that occur close to the sun. According to theoretical models, such events can only take place within magnetic fields stronger than 100 microteslas — far greater than what Fu and his colleagues measured."
"Jerome Gattacceca, research director at the European Centre for Research and Education in Environmental Sciences, says the solar system would have looked very different today if it had not been exposed to magnetic fields. "Without this kind of mechanism, all the matter in the solar system would have ended up in the sun, and we would not be here to discuss it," says Gattacceca, who was not involved in the research. "There has to be a mechanism to prevent that. Several models exist, and this paper provides a viable mechanism, based on the existence of a significant magnetic field, to form the solar system as we know it.""
my bold. ]
The model paper show an averaged field strength within a 0.3 Gauss range in their model set [figure 6], which is a 30 micro Tesla range.
Seems to fit very, very, very nicely together!