Re: What would happen if aliens evaporated all the oceans to steal the salt?

>Can that much water even BE evaporated into the atmosphere?

Yes, we could have an atmosphere that was effectively 100% water vapor (steam), though of course without continuous input of energy it would return to the 2-3% (mol fraction = fraction of molecules in atmosphere, somewhat different from mass fraction) which is what we get with the energy from the sun. Note that the greenhouse effect, caused by water vapor in the atmosphere, does result in slightly higher water vapor in the atmosphere, but to double the amount of water vapor in the atmosphere would require changes to the energy budget much greater than anything caused by greenhouse gases. Of course, your question is about aliens boiling the oceans, so...

>(Assuming the ice caps melt too. Would they re-freeze?)

Yes, they would refreeze. However, the amount of ice stored in the polar caps might take hundreds of thousands or millions of years to return to equilibrium.

>Would the rest of the planet get hot too?

If aliens boiled the oceans, yes. Half the planet's population lives within 100km of the coast, they would be boiled right along with the ocean. The rest of us would merely be subject to scalding-hot rains.

>How long would it rain?

That's a difficult question. Basically, the oceans would rain back out once the excess heat used to boil them was radiated back into space. That's a good problem for a college physics class.

For further reading along these lines, I would recommend How to Destroy the Earth, a very convenient reference.

Good luck!