Goldilocks zone
attrib.— «The carbonates, they determined, had indeed originated on Mars and, more astonishing, had formed in what scientists call “the biological Goldilocks zone—not too hot, not too cold, and, conceivably, just right for life to exist.”» —“Rock of ages” by M.G. Lord Los Angeles Times Feb. 26, 2006. (source: Double-Tongued Dictionary)