The Moon's Two Sides Look So Different Thanks To 4.5 Billion-Year-Old Physics (forbes.com)

StartsWithABang writes: 4.5 billion years ago, a giant object collided with our proto-Earth, kicking up debris that eventually coalesced into the Moon. While the near side contains dark maria and lunar lowlands, the far side is almost exclusive heavily cratered, high-mountainous regions. This was a mystery for a long time, but it appears that heating from the hot, young Earth caused a chemical and crustal difference between the two faces.

Comments

Re:I could be missing something

[rasmusbr]

Another interesting aside is that many have tried to explain gravity by postulating that the universe is full of tiny particles that fly about randomly in all directions and that gravity works because bodies block the particles from hitting one another.This is sometimes called the screening theory of gravity.

If you make some reasonable assumptions you will find that two nearby bodies would block particles from hitting one another, creating forces that follow the inverse square law...

These theories also predict that planets will de-orbit and crash into their stars, and that moons will similarly crash into their plants. But hey, no theory is perfect.

Re:How could the Earth heat it?

[Michael Woodhams]

1 billion years ago the Earth had 100 to 1,000 foot tides as the Moon and the Earth were much closer

My initial response is "I don't think so." My second response is to calculate, so here goes:
Current distance to moon = 384,400 km = 4 x 10^8m
Current rate of increase in distance to moon = 3.8 cm/year = 4 x 10^-2 m/year.
If this rate were constant over a billion (10^9) years, then a billion years ago the distance to the moon was 4 x 10^-2m/year*10^9year = 4 x 10^7 m closer, or 10% closer. Tidal effect strengths are inverse-cube in distance, so a billion years ago, lunar tides would have been about 30% larger than now.

This doesn't come close to "100 to 1000 foot tides."

Re:How could the Earth heat it?

[Namarrgon]

Good, but the rate of increase in distance to the moon isn't constant (it was faster in the past), and it's thought that the moon formed at a distance of only about 20 to 30 thousand kilometers.

By your maths, 4B years ago would've put the moon at 60% its current distance, but at formation it is more likely to have been only 6% of current distance. Assuming similar mass to today, 60% closer implies more like 4.6x the current tidal force - but 6% distance might be 4,600x stronger forces (probably more, given that the distance to the Earth's surface was even closer). How this translates into actual tidal sizes is left as an exercise for someone who knows more than I do.

Of course back then there probably wasn't much water around, given terrestrial temperatures in the thousands of degrees, but there may have been some impressive magma tides instead.