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Originally Posted by Linus
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Okay, now I'm back.
Here's why O'Reilly is wrong (I know shocking!):
1) "How did the Sun get there?" Remember that gravity is the warping of space-time by mass and is ALWAYS attractive. So dust in our little corner of the Milky Way is attracted to other parts of dust. These bits of rock and dust start to clump together and orbit one another. The more matter that gathers, the more mass and therefore the more matter that is attracted. At some point *enough* mass is collected that it begins to compress at which point a critical mass is formed and a star is born! That's a LOT of mass but we have caught Nature in every stage of that act in the last 50 years or so.
2) "How did the Moon get there?" The early solar system was a chaotic mess. Not ALL of the material in the solar system went to making the Sun, some of it went to make planets. When the Earth was very, very, very young (less than a billion years old), it collided with something that smaller than the Earth. It would have been a glancing blow but it would have torn the smaller planet apart. When it reformed the Earth had a convenient large moon. How do we know? For one, our rotation is not perpendicular to the plane of our orbit. The Earth is actually tilted at 23 degrees (which is why we have seasons). That kind of thing strongly suggests an impact that knocked the Earth off of a perpendicular axis of rotation. (This has happened to at least one other planet, Uranus, which actually is tilted 90 degrees so, unlike the other 7 planets, it doesn't have a north or south pole but a East or West pole) Our moon actually stabilizes our rotation along with creating the tides.
3) "Why doesn't Venus have that?" We don't know why Venus doesn't have a satellite but it doesn't. Not every planet can be in the position to have a satellite.
4) "Mars doesn't have that?" Mars has two moons Deimos and Phobos. Most likely these are asteroids that were captured by the planet (Mars has a mass similar to Earth's)
I think that just about covers it.
