Dave, London asked:
I would like to know what would happen to the Earth if a meteor hit the moon and destroyed it - the weather and the tides and gravity, and stuff like that. How would that be affected if the moon was destroyed?
Dave - Okay. There are two questions there. If a meteor hit the moon and blew it in to thousands and thousands of pieces, what would happen to the Earth? The short answer is that we would have a nuclear winter. You would put huge amounts of rock into the atmosphere. It would block out the sun.
Chris - It will actually reach us, would it?
Dave - If it hit hard enough to blast the moon into millions of pieces, then there would be enough energy that a significant portion of the moon would land on our atmosphere. You’ll get huge amounts of dusts in the atmosphere. All the plants would die.
Chris - Because some people suggested that one way to mitigate against global warming is in fact to create a cloud of dust by mining the moon and ejecting material into orbit in the same orbit as the moon, therefore, creating a sort of buffer against solar influx, and this would cool down the Earth a bit.
Dave - Yes. If you completely destroy the moon, it would be like that...
Chris - In fact it would cool down a lot!
Dave - A billion times over! And the Earth would be a pretty nasty place. The other question is if you just got the moon and took it away, and disappeared it somehow, what would happen? You’d immediately lose the tides because those are due to the moon’s gravity. And also, on a longer term, there would be some subtle effects; the axis of the Earth is actually stabilised by the moon orbiting it. The moon’s got huge amounts of angular momentum, so perturbations don’t tend to have a very large effect on it and it tends to stabilise the direction of the Earth’s axis over millions of years.
So, if you then waited millions of years, the Earth’s axis would rotate and that could have all sorts of complex effects on the weather and life in general and also not having tides could have all sorts of strange effects on weather because you’re not mixing the oceans and the oceans move far more energy around the Earth than the atmosphere does.