Thursday, October 1, 2009

Chapter 3 - The Earth - From Blue Giant to Blue Marble

Saying that the Earth is unique is an understatement. The Earth has minable quantities of all the elements - i.e. very rich in minerals. It has huge quantities of water and plenty of gas (nitrogen, oxygen, etc.). The core's magnetic dynamo protects us from the solar wind and the ozone layer protects us from UV radiation. The Moon itself "sweeps" up comets and asteroids while creating tides that help drive the weather. The axial tilt gives us the seasons - which are a dynamo for life. The Earth is truly a gem.

In simple terms, moving the Earth in one direction would "shorten" the Moon's orbit on that side and lengthen it on the other. Either the Moon's orbit would become more and more elliptical or it would need energy to pull its orbit back into a (larger) circle. It already has a mechanism to get energy (pulling on the Earth's tides), so this is a possibility.

The Earth can only move away from the Moon in one of two ways; either it is accelerating away from the Moon, or it is moving in a certain direction which the Moon is not. The data disproves number one as the retroreflector ranging shows that the Moon is moving away from the Earth at a constant velocity. As for the second assertion - we need more data! Let's examine the Earth/Moon system in more detail.

The CSB says that the Moon was created from the impact (The Big Whack) of a mars-size planetoid (Theia) into the Earth. There are 3 different scenarios for this impact:

  1. Theia and Earth were in the same orbit - in this case there would be no velocity vector toward or away from the Sun (like a car running into you from behind or from the front, your car stays on its original path - with its velocity changed).
  2. Theia strikes the Earth at an (oblique) angle - in this case the Earth gets "pushed" away from its original trajectory - but it eventually returns to a stable orbit, albeit closer or further away from the Sun (if your car gets sideswiped, you keep moving in the same direction, but you move laterally away from the impact and eventually recover - albeit in another lane).
  3. Theia strikes the Earth at a right angle - in this case, the Earth gets pushed away from its original trajectory - but it (may) never return to a "stable" orbit (your car gets T-boned) i.e. it depends on whether Theia ever "stops".
Number 3 is the only scenario where Earth can continue to alter its orbit - i.e. moving away from the initial impact location.

The CSB on Theia is that it formed close to the Earth (maybe at a Lagrange point - where the Sun's gravity and Earth's gravity cancel each other out), and then was disturbed from its orbit - putting it on a collision course with the Earth. I fail to see how a planetoid that was orbiting in the same direction as the Earth could move laterally and strike the Earth perpendicular to that orbit. It would most likely impact like a sideswipe or a head-on and not like a T-bone (or a rear-ender).

Assuming that the impact was a "T-bone" like event, then Theia would have had to either come from the direction of the Sun or from the opposite (Jupiter side). The first possibility is that Theia formed close to the Sun - which somehow "threw" Theia at the Earth. The second possibility would include Jupiter's gravity 'disturbing" the asteroid belt which dislodged Theia - but that would be a much harder "shot' as Jupiter is 5x further away from the Earth than the Sun (and has less gravity). It makes more sense that Theia hit the Earth from "inside" (Sun side) of its orbit (possibly accelerated and steered by the Sun's gravity) - causing the Earth to move away from the Sun. This means that the Earth's "year" would get longer - thus necessitating adding leap seconds . . . 


Proposal 1

The Earth is moving away from the Sun

because of the (initial) Theia impact and Newton's 1st Law Of Motion (a body in motion stays in motion unless acted upon by an outside force). The Moon gains energy from pulling on the Earth's tides and can increase its orbit in line with Earth's motion away from the Sun.

A consequence of Proposal 1 is that the Moon's perihelion (closet approach to the Sun) is a constant (distance), assuming that the Moon is not also moving away from the Sun (it isn't).




Lets make a model

Think of the Earth as a rubber ball with a (hard) coating of plaster.

What happens when you toss it up and hit it with a baseball bat? Poof! You get a cloud of plaster dust while the rubber ball shoots far away. Theia intercepted the Earth in a perpendicular crossing route - like the bat. The Big Whack (and CSB) says that Theia merged with the Earth and (part of the Earth's) outer crust was thrown into orbit - where it formed a (dust) ring and then accreted into the Moon.

The rubber ball model is not complete enough so we need to add more information to the model. The Earth (ball) is always in motion orbiting the "center" (Sun). So visualize a (fast) rotating platform with a T-ball set up. When the ball is hit, it flies far away while the plaster would tend to more concentrated in a smaller area (like a centrifuge). The plaster pieces (mostly) have the same trajectory before AND after the impact.

This illustrates that there was not a "ring" of material from The Big Whack - more like a blob. This blob also retained the original orbital trajectory as the Earth (pre-impact). It was this blob that coalesced to form the Moon.


Proposal 2

The Moon's perihelion (closest approach to the Sun) marks the original orbit of the pre-impact Earth.

The Moon's material has not moved relative to the Sun since its formation (as part of the pre-impact Earth). The Moon is the "original" Earth.

When the Apollo astronauts brought rock samples back from the Moon,scientists were hopeful to find rock that might have come from Theia. This would have been a very important find as it would answer many questions about The Big Whack. They did not find anything that could be considered a candidate Theia sample.



Conundrum 7: Missing rock evidence for Theia

Where are the samples?

No solid rock evidence of the Theia impact means that The Big Whack theory needs to be changed.



Proposal 3

The Moon formed from a "blob" of material that occupied a relatively small region of space.

It coalesced into the Moon relatively quickly - thus (highland) moon rocks have a consistent (very ancient) age of 4.6 Gya (not much changed from the pre-impact Earth).

NOTE: Erik Asphaug recently proposed a theory that the Moon was actually 2 blobs that "soft impacted".

This impact created the axial tilt (23 degrees) of the Earth. There are also other planets with similar axial tilts - Mars (25 degrees), Saturn (27 degrees) and Neptune (29 degrees). The tilts are very similar - could their tilts be caused by the same impact mechanism? A single explanation that would cover all of these cases would be more plausible than separate events. . . .

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