A rare book predicting alien life could sell for thousands at auction.
The book, published in 1698, was found at a free antique valuation event in Moreton-in-Marsh, Gloucestershire, by books valuer Jim Spencer.
Inside, author Christiaan Huygens explores his fascination with the potential existence of extra-terrestrial beings.
Mr Spencer said its contents seemed "almost comical".
The book, lengthily entitled The Celestial World Discover'd: Or, Conjectures Concerning the Inhabitants, Plants and Productions of the Worlds in the Planets, Huygens questions why God would have created other planets "just to be looked" upon from Earth.
He concludes that aliens must have hands and feet like humans because of their "convenience", writing: "What could we invent or imagine that could be so exactly accommodated to all the design'd uses as the Hands are? Shall we give them an Elephant's Proboscis."
He also suggests that "celestial beings" must have feet "[unless] they have found out the art of flying in some of those Worlds".
The writer believed aliens enjoyed astronomy and observation, sailed boats and listened to music but also suffered misfortunes, wars, afflictions and poverty "because that's what leads us to invention and progress".
The book is considered such a rare find that it will have a guide price of £2,000-£3,000 when it goes to auction in July.
Mr Spencer said: "It's fascinating to think who turned these pages in 1698, what they must've felt when reading these descriptions of life on Jupiter or Saturn before gazing up at the night sky."
He said the antique book's content seemed "almost comical", but was informed by scientific reasoning of the time.
"And who knows how our own thoughts on these matters will appear to people looking back in 324 years," he added.
The book valuer said flicking through the pages gave a "curious feeling" due to its subject matter belonging to the future or science fiction, "yet the writer is speaking to us from the past".
"I found myself realising that we've since explored not only more of space, but more of our own planet."
He said the author ruled out the possibility of much larger animals than those currently existing on Earth because it was written before humans knew about dinosaurs.
"I think the subject matter is so compelling because it makes us chuckle at what they didn't know, while staring up at the heavens and realising it's still a mystery," Mr Spencer said.
The book is listed for sale on 5 July in Hansons Library Auction at Bishton Hall in Staffordshire.