To qualify, a planet has to orbit its star at a distance far enough so that water does not evaporate in the solar heat, and near enough that it does not freeze beyond the rays' reach.
Water is considered an essential requirement for life, however primitive.
Churchill first drafted the paper in 1939, when Europe was on the brink of war, and revised it in the late 1950s while visiting his publisher in a village in the south of France, said Livio.
As far as could be determined, the work has never been published or subjected to scientific or academic scrutiny.
"What is extraordinary is his train of thought, he thinks about the problem like a scientist," Livio told AFP of the find.
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The concept of habitable zones originated in the 1950s, the same decade in which Churchill finished his essay.
A war correspondent and soldier turned politician, Churchill was also known for his love of science.
He wrote essays and articles in the 1920s and 1930s on topics including evolution, cell biology and fusion power.