Question: How much closer to the sun would Earth have to be for it to be unihabitable? How much further away fromthe sun would Earth have to be for it to be unihabitable?

Arttu Rajantie answered on 22 Jun 2011:

This is known as “the Goldilocks problem”, because like the little bear’s porridge in the story, the Earth is not too hot and not too cold but perfect for life. I think it is hard to know for sure because life on Earth has adapted to the temperature that the Earth has, and we don’t really understand the atmosphere well enough. Some early estimates suggested that the Earth would be inhabitable if it was just a few percent closer to or farther from the Sun, but I think these days people are talking about a few dozen percent.