It isn’t unreasonable to speculate that extraterrestrials have visited Earth. The Milky Way is aged and immense, with copious habitable planets, granting other intelligent species plenty of time to master sub-light speed interstellar travel and conduct ranging expeditions lasting centuries or more.
Imagine: if an intelligent extraterrestrial species briefly visited Earth once every 15,000 years or so, there’s no way we would know today. After all, the earliest writing only dates back to 3,400 BC, so if aliens landed and made a few quick pit stops before then, we wouldn’t be any the wiser.
But what if extraterrestrials did land on Earth thousands of years ago and their visitation was recorded in the early writing of the day? What might such a depiction look like? Venerated science communicator and astrophysicist Carl Sagan speculated on that very subject with colleague Iosif Shklovsky in their 1966 book Intelligent Life in the Universe.
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