It is difficult to be precise about the size of the Sun’s ‘habitable zone’ because it depends on many complicated factors, including solar irradiance, atmospheric composition, cloud and weather patterns, the reflectivity (or ‘albedo’) of the Earth’s surface, and so on. But the latest research actually suggests that the inner edge of the Solar System’s habitable zone is between 0.95 and 0.99 astronomical units.

That means the Earth would become uninhabitable if its average distance from the Sun was reduced by as little as 1.5 million km – which is only about four times the Moon’s distance from Earth!


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