pavelcherepan

Those are velocities with respect to each other. So the velocity of Theia relative to the Earth. OK? I gave you the terminal velocity. Point 5 it is.

Sorry, mate, but you clearly have no idea what you're talking about. Both the planet coming from L3 and the planet coming from L4,5 will start at "the infinity" where gravitational influence of the Earth is negligible and will pass through entire Earth's gravitational well and get the same amount of acceleration. Your example is another logical fallacy where an analogy is used but such analogy is not applicable to the situation. Let's do the maths because you clearly can't. Let's define 5 points - point 1 is the L3 Lagrangian point, point 2 is L4, point 3 is 50 million km away, point 4 is 10 million km away and point 5 is the impact with the Earth. And let's use some reasonable starting velocity ~ 1km/s. Point 1. r = 3*1011m escape velocity with regards to the Earth ve = 44.62 m/s orbital velocity [latex]v_{orbital}=\sqrt{v_e^2 + v_{\infty}^2} = \sqrt{44.62^2 + 1000^2} = 1000.99 m/s[/latex] Point 2. r~1.5*1011m ve=63.10 m/s [latex]v_{orbital} = 1001.99 m/s[/latex] Point 3 r = 5*1010 m ve = 109.3 m/s [latex]v_{orbital}=1005.96 m/s[/latex] Point 4 r = 1*1010 m ve= 244.4 m/s [latex]v_{orbital}=1029.43 m/s[/latex] Point 5 r~6*106m (from the center of the Earth) ve ~ 9977.4 m/s [latex]v_{orbital}=10027.45 m/s[/latex] First of all, can you see that even within 10 million km from the Earth it's gravitational influence is tiny - just adds 30 m/s to orbital speed and also the fact is that co-orbital object starting from L3 will have to go through L4 or L5 on the way to Earth and it doesn't matter if the object just starts from there or it's passing by with the same initial velocity the velocity at L4/5 will be the same. And as always:

Is that so? I think that its in fact quite well established and studied based on spectral data. <Metallicity>

I believe you meant 4.5 by, not my, right? That's why we use meteorites. They are pretty much unchanged from the time of their formation and they all agree on the same age as I've shown in the quote in the previous post. Also your calculation contradicts basic cosmology/astronomy as with that kind of age the Earth must've formed around Population III or Population II star which all have very-very low metallicity and are supposed to be huge and die quickly within millions of years none of which we're observing. Also there wouldn't be enough silicon, iron and oxygen to form a rocky planet at that time. How much contradictory evidence do you need to finally agree that your estimate is wrong-wrong-wrong?

4.1*109yr - 4.04*109 = 0.06*109 yr = 60*106 yr. That's what current models say. Difference between what and what? You got me confused here. Any evidence for those coming my way?

That's why I said 10-11. Actually, using [latex]v_e=\sqrt{2GM/r}[/latex] and using mass at 75% of current we get escape velocity at surface of 9.98 km/s. So then impact velocity will be roughly 10 km/s. What do you not understand from this? Geological evidence (we have rocks dated at 4.04 bya, plenty of zircon crystals etc.) show that conditions on the planet were different from what you'd expect from 60 million years post impact. By the way, what about:

It said 4.1 billion years ago (bya). Can't you do ratios? If at 1 km/yr the trip of 471 million km takes 471 million years, then in x km/yr it will take 300,000 years. What is x? Relative velocity of the impact will be 10-11 km/s which depends on the escape velocity from Earth's surface and hence on mass of the Earth at that time.

Oh, haven't noticed that it was 1 km/year. In that case it would obviously take 471 million years. The relative velocity will only start increasing very-very slowly when Theia gets as close as 50 million km from Earth and even then it would hardly be noticeable. So it's pretty safe for the rough calculation to use 1 km/yr for the entire trip. Impact would occur at more or less 10-11 km/s relative and at ~4.1 bya which largely contradicts all geological evidence.

Here's a link to Wikipedia's article on list of logical fallacies. I've linked it straight to Informal fallacies because they're the ones that you encounter more often.

I'm not going to argue Stefan-Boltzman law with you. I'm not qualified enough for that and there are plenty of physicists about who can do it better, but what I am qualified to argue about is geological evidence and you can't just go and disregard it because that way your (apparently incorrect) calculations work better.

[latex]2 \pi r = 2*3.14*1.5*10^{11} m = 9.42 * 10^{12} m [/latex] roughly for the entire orbit and [latex]4.71*10^{12}m[/latex] for half orbit. At say 4 km/s it will take ~37.4 years. At 1 km/s it will be ~149 years. Laughable in geological scales. You can't build much mass within such a short a timeframe as shown in the article for planetary accretion I linked in post #51. And hence the best option is that Theia had formed in stable L4 or L5 where it could accrete mass for a long period of time and then got thrown out of there due to influence of other celestial bodies.

Your attention to details and disregard of contradicting evidence is baffling. Meteorites formed from the same nebula that formed the Earth and around the same time and also due to smaller size of meteorites and asteroids they were never largely molten and so give us a better understanding of the time of formation of Solar System. <Age of meteorites and Earth>

I have indeed made such claim, you got me there, but then again, I made a claim and provided evidence that it is highly unlikely in posts #35, 39 and 41. Where's the proof? Where's the proof? Proof?

What about meteorite dating? Those contradict with your calculations too.

David, your "real answer" disagrees with geological evidence. Please explain how you plan to account for that?

Argument from ignorance (argumentum ad ignorantiam) - " assuming that a claim is true because it has not been or cannot be proven false, or vice versa." and you should look at the following too: onus probandi incumbit ei qui dicit, non ei qui negat - "the burden of proof is on the person who makes the claim, not on the person who denies" No reason to discount it but no reason to accept it either. And in order to be accepted it should come with some proof, which you have none of.

1. Is a logical fallacy. The fact that nothing says it couldn't doesn't mean it could. 2. I see no proof here at all. Just same logical fallacies as above. 3. I'm waiting. Wrong. What about quote from post #41? Did you even read it?

Robbitybob1, I would show you references to L3 if there were any models that presumed that Theia could form there, but there are none. Any why in the world do I have to provide references to support your position? Shouldn't you do it? I'd really love to see one or all of the following from you: 1) Link or quote from any reference that suggests that Theia could've formed at L3 Lagrangian point. 2) Link or quote that suggests that 105 years is enough to form a Mars-sized planet 3) Calculation that proves that object coming from L3 would impact proto-Earth at higher velocity than object coming from L4 or L5 with same initial velocity. Unless I see any of those, what you're doing here is soapboxing and as long as I keep providing you with proper evidence and you just keep saying random stuff without any sort of proof there's nothing to discuss here, is it? Ciao!

I've done that before and I'm happy to do so now. I have yet to see any figures from you, though. From the paper <Terrestrial planet formation> Page 9: Page 17: And these describe the final stages of formation after planetesimals have been formed so my initial estimate was even off by an order of magnitude. In the same paper you can read up how stable were orbits in the system based on N-body simulation. 100,000 years in L3 would not happen and even if it did it's 2-3 orders of magnitude smaller than required for Mars-sized body. So you still haven't read the links I gave you on orbital mechanics. Really there's no point discussing it unless you understand what [latex]v_{\infty}[/latex] refers to. Here is a quote from NASA site for Theia formation:

That's not how supernovas work. Supernova happens when a massive star runs out of fuel in its core and electron degenerate pressure is not able to support against the weight of outer layers and then it starts collapsing onto itself. In that case there'd be a center of expansion. Universe doesn't have one.

iNow,nuclear power generation was mentioned in the OP, so we're all good here

I wasn't being condescending. I said that what you believe matters not if it disagrees with physics and mind you, we're not even in Speculations, we're in Classical Physics forums. If you think otherwise please find any study that proves that Theia could've formed in L3 or any physics-based proof for that and I will happily discuss that with you. Estimation. At present Venus creates major disturbance at L3 every 20'ish months. Back during the formation of Solar system Venus would be smaller, but the Earth would be smaller too and also there's be plenty of various planetesimals wondering around that would disturb the L3 objects too. I can't estimate how long exactly the object can stay stable in that point at that stage but even if we take the best-case scenario and say that it could stay there for a 100,000 years (which is enormous overestimation), but formation of a Mars-sized planet takes in excess of ten millions years which is two orders of magnitude longer that our gross overestimate for L3 stability. Maybe something did form there, but definitely not Theia.

It most certainly doesn't. The L3 point is unstable and there's not enough time for a planet the size of Mars to form before it's kicked out of the orbit. Did you even read the sources I quoted?

Trojan planets, asteroids etc can only form in L4 and L5 for Sun-Earth system, all other L-points are unstable for various reasons. And the term "Trojans" only refers to objects at L4 and L5 points. And here's why there can't be anything in L3: OK? What you believe is irrelevant. Probably you don't understand what hyperbolic trajectory is and what velocity at infinity is. So please read up on the relevant entry in Wikipedia or in the following link <Basics of Space Flight>.

I really have no idea what you're talking about. There's no specific limit of velocity for the Giant Impact and the number of [latex]v_{\infty} = 4\, km/s[/latex] was taken from the simulation of GI so there's no need to prove it recursively. What does L3 Lagrangian point have to do with it? Anyway, if a planet is coming from L3 for some reason and if [latex]v_{\infty}[/latex] is still 4km/s then impact speed will be exactly the same based on this: [latex] v^2 = v_{esc}^2 + v_\infty^2 [/latex] [latex]v_{esc}[/latex] and [latex]v_{\infty}[/latex] will be the same and so the impact velocity will be exactly the same. But then again, L3 point in Sun-Earth system is widely unstable and no sizable body could've formed there.