LONDON — Even as he was preparing for the biggest struggle of his life, leading Britain in its fight against Nazi Germany, Winston Churchill had something else on his mind: extraterrestrials.

In a newly unearthed essay sent to his publisher on Oct. 16, 1939 — just weeks after Britain entered World War II and Churchill became part of the wartime cabinet — and later revised, he was pondering the likelihood of life on other planets.

Churchill, who went on to become prime minister during much of World War II and again from 1951 to 1955, was so enthralled by the subject that he even ordered a suspected sighting of an unidentified flying object by the Royal Air Force to be kept a secret for 50 years to avoid “mass panic.”

In an 11-page essay titled “Are We Alone in the Universe?” the statesman showed powers of reason “like a scientist,” said Mario Livio, an astrophysicist who read the rarely seen draft and wrote about it in an article published on Wednesday in Nature magazine.