= Solution
The <circumstellar habitable zone> is the range of orbital distances where a terrestrial planet with a specified atmospheric inventory can retain liquid <water> at its surface. It is a conditional climate criterion, not a guarantee of life or a requirement for every possible subsurface habitat.
Four influential factors are:
* The incident stellar energy and spectrum, including orbital distance and long-term stellar evolution.
* Atmospheric pressure and composition, <greenhouse effect>, <Bond albedo> and clouds, which set the relation between absorbed light and surface temperature.
* The <water> and volatile inventory, together with planetary mass and the ability to retain or replenish an atmosphere.
* Internal and surface evolution, including <plate tectonics>, outgassing and the <carbonate-silicate cycle>, which can regulate climate over geological time.
For a Sun-like present-day star and an Earth-like planet, \b[a useful conservative range is approximately $0.95$–$1.7\,\mathrm{AU}$]. The inner limit depends on the adopted moist or <runaway greenhouse> condition, and the outer limit on the <maximum greenhouse outer habitable-zone limit>. More restrictive water-loss choices put the inner edge near $0.99\,\mathrm{AU}$. Empirical optimistic limits based on past <Venus> and <Mars> are about $0.75$–$1.8\,\mathrm{AU}$. These are model conventions rather than exact universal boundaries.
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