Now that really seems like an obvious mistake. We know that liquid water is found on the earth and that it is within a habitable distance from the sun. So why put out a paper that is essentially saying the earth isn't habitable? Well, it actually doesn't say anything like that at all. The paper defines the distances from the sun that liquid water is most likely to exist. It's not a definition or even a strict cut-off point for habitability. In the abstract, the authors even clear state:
"Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given."Clouds. Clouds reflect sunlight away from the earth, taking heat away. So this new definition doesn't say that the earth uninhabitable, it defines a possible range where planets would be habitable (not taking into account cloud coverage). Some reports are already trying to showcase the "stupidity" of scientists, but they really misunderstand the purpose of the research. This is simply a model - our best guess, given certain assumptions - and since we don't know very much about other solar systems it's good to have a good guess of where to look, and that's what this range gives us.