Thursday, October 1, 2009

Chapter 5 - Theia - From Blue Giant to Blue Marble

Momentum (p) equals mass (m) times the velocity (v); p = mv. You can increase either m or v and you increase momentum (p). In the case of The Big Whack, I believe that both of these would need to be very high. A good Physics student could model this by calculating the force vectors and using the bulk modulus of the material etc., but I doubt that you could understand everything that happened in the impact. So I will do this with analogy and hand-waving instead . . .

Let's construct a (more accurate) model for the Earth. Fill a bowling ball sized balloon with thick tar (the Earth would not have been totally solid at this point in time [4.6Gya] - in fact it would have been mostly molten inside. That's why I chose thick tar for the model) and then cover the balloon with plaster (paint it blue) and set it on a table (having Atlas hold it on his shoulders while standing on turtles would be more appropriate). This is a good approximation of the Earth as the continental crust is fairly rigid while the mantle is ductile. Now let's model an impact!

Take a baseball and throw it at the balloon (the baseball is Theia), what happens? The baseball bounces off the balloon and shatters the area around the impact. There might be a bulge on the other side of the balloon from the impact - with a few cracks in the plaster. Now that wasn't a good enough impact. We need MORE POWER!

Now let's take a cannon ball (same size as the baseball) and fire a cannon at the balloon (after fixing the plaster).


Figure 16 US Marines in Iraq firing howitzer

Now what happens? As the cannon ball hits, it keeps going into the balloon. This expands the balloon (the added volume of the cannon ball), which cracks the entire plaster surface, and the plaster goes flying. On the side opposite where the cannon ball impacted, goopy tar gets blown out (displacing tar the same size as the cannon ball), but most of the tar stays put since there isn't any (much) force being applied to it. The balloon then flies off the table as the force of the impact gets absorbed by the tar and translated into movement of the balloon. So now let's look at the results.

The table is covered with plaster (there is also some plaster on the floor). There is a blob of tar (far away) on the floor along with a balloon with a cannon ball embedded in the center of it. Oh yeah, the cannon ball also pushed some of the plaster into the balloon tar. This experiment looks pretty accurate - you should be able to actually do this test (don't do it at home!).

The plaster (on the table) represents the Moon as the dust comes together around the initial impact to form the Moon (in the same place as the pre-impact Earth). The blob that came out the back represents Mars - and since most of the momentum of the cannon ball was translated into the tar blob - there would be enough energy for the blob to fly far from the initial impact. The balloon represents the Earth - with a metal core, moving away from its original orbital position. And that piece of plaster that was pushed into the tar by the cannon ball represents Australia (Pangaea)! NOTE: The (land) surface area of the Earth is almost the same size as the entire surface of Mars (149 million sq. km vs. 145 million).

That certainly sounds plausible! This would also explain why you don't see any remnants of Theia on the Moon (or Earth) today (it was solid iron). This also explains where Mars got its tilt and rotation from (the tar blob was rotating the same as the rest of the Earth, and the impact tilted the Earth as the blob was being shot out).

As Theia approached the Earth closer and closer, it would have pushed the atmosphere away before it impacted. This atmosphere would "bunch up" on the other side of the Earth. The impact would also cause tremendous heat - which would vaporize any water on the side of impact - creating steam, which would go into the atmosphere (which is bunched up behind the Earth). When the tar blob (Mars) exited the balloon (Earth), it would go right though the thickest part of the atmosphere. Mars' gravity would have grabbed a chunk of the atmosphere (which had water in it).

Note: Venus' atmosphere is 93 times as dense as Earth's - even though they formed in nearly the same area (and they are almost the same size). Why is Venus' atmosphere so dense? Maybe a better question is why is Earth's so thin (in relation)?

There was also enough steam to mix with the plaster (Moon stuff) which is where you get those nice spheres from off the Moon. NOTE: Not all of the plaster was used in the formation of the Moon. Some of it was blasted out of the "general neighborhood" of the Earth/Moon and became asteroids. We will talk about that later. Some of it certainly fell back onto the Earth.

But we need to know more about Theia.



Conundrum 10: Origin and composition of Theia

Where did Theia come from and what was it made out of? Was it solid iron?



Conundrum 11: High velocity of Theia

How the heck did Theia get moving so fast?

Since the remnants of Theia sit at the center of the Earth today, what do we know about the Earth's core? This should give us some hints for answering those Conundrums.

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