I wouldn't count on an orphaned planet being life-bearing. While it's possible, the chances are probably the chances of finding an Earth-like planet, squared, and applied those odds only to orphaned planets. Which are hard enough to find as it is. It'd be like finding a needle in a hundred billion exploded haystacks, in which there is a light year between each piece of hay and the needle is made of straw. In the dark.
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