= Solution
For an Earth-mass planet with a nitrogen-carbon-dioxide-water atmosphere, commonly quoted conservative Solar boundaries are approximately
$$
\boxed{a_{\rm in}\simeq0.95\,{\rm AU}},
\qquad
\boxed{a_{\rm out}\simeq1.67\,{\rm AU}}.
$$
The inner edge is governed by moist-greenhouse water loss and ultimately the <runaway greenhouse>. The outer edge is the <maximum greenhouse outer habitable-zone limit>, where additional carbon dioxide condenses or increases reflected light faster than it increases infrared trapping. Optimistic empirical boundaries, based on recent Venus and early Mars, are broader, roughly $0.75$ to $1.77\,{\rm AU}$. The values depend on clouds, planetary mass, atmospheric inventory, and climate assumptions.
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