Prepare Yourself for Little Green Men

‘Extraterrestrial: The First Sign of Intelligent Life Beyond Earth,’ by Avi Loeb (2021)

In 2017, a telescope in Hawaii noticed a strange object careering through the solar system. Was it just a weirdly behaving comet? Loeb, a prominent astrophysicist at Harvard, came to a bolder conclusion: The object, christened “Oumuamua” (Hawaiian for “scout”), could well be the product of an alien civilization — the first proof of intelligent life outside our planet. “If we dare to wager that Oumuamua was a piece of advanced extraterrestrial technology, we stand only to gain,” he writes in this book arguing his case, which doubles as a poignant memoir of his childhood on an Israeli farm and his passion for space science.

‘The Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves,’ by Arik Kershenbaum (2021)

If and when we finally make contact with extraterrestrials, what will they look like? Who better to ask than a zoologist who knows every permutation of living being. Kerschenbaum comes to some surprising conclusions: Some version of Darwinian selection would be at work in any life form — and alien evolution will probably follow the path of our own, limiting the menu of possibilities. For one thing, he thinks they’ll be bilaterally symmetrical, like us, with two eyes or two legs — or maybe two antennae.

‘Aliens: The World’s Leading Scientists on the Search for Extraterrestrial Life,’ edited by Jim Al-Khalili (2017)

This collection, edited by Al-Khalili, a quantum physicist, gathers experts who have looked up at the night sky and pondered the question: Where is everybody? The consensus is that aliens will look and act nothing like the way we imagine them in the movies. As the astrophysicist Martin Rees explains in his essay, we will most likely encounter some kind of machine intelligence rather than actual beings. They might even be speaking to us now, though we aren’t equipped to understand them. “Even if the search succeeded,” Rees writes, “it would still in my view be unlikely that the ‘signal’ would be a decodable message.”

‘Area 51: An Uncensored History of America’s Top Secret Military Base,’ by Annie Jacobsen (2011)

No two words in the American lexicon more quickly summon images of little green men and hovering white disks than “Area 51,” the mysterious test range in southern Nevada. Jacobsen’s dogged investigation uncovered little about aliens and U.F.O.s — she discounts some of the rumors as Cold War intrigue — yielding instead a provocative account of top-secret nuclear arms testing and research into aerial espionage technology.

‘The Varieties of Scientific Experience: A Personal View of the Search for God,’ by Carl Sagan (2007)

Sagan died in 1996, but this book, released 10 years later, gathered some of his lectures, capturing his wonderment at the cosmos. Sagan took pleasure in the unknowability of what was out there, particularly with regard to alien life. He was happy to have something he called “faith” in the existence of other worlds — he famously created the “golden record,” meant for any extraterrestrials who might encounter the Voyager space probe. These lectures are marked by this openness to what is yet undiscovered: “I think if we ever reach the point where we think we thoroughly understand who we are and where we came from, we will have failed.”

‘Abducted: How People Come to Believe They Were Kidnapped by Aliens,’ by Susan A. Clancy (2005)

How to explain the vivid memories of people who think they’ve been kidnapped by Martians? Clancy, a Harvard-trained psychologist, interviewed dozens of self-described abductees over a number of years and produced this comprehensive 2005 study that, in the words of the Times science writer Benedict Carey, “manages to refute and defend these believers.” Clancy takes seriously the abductees’ accounts of having experienced something transformational while offering the most likely scientific reasons for these beliefs: a combination of the disorienting effects of sleep paralysis with the suggestive images of pop culture.

‘Rare Earth: Why Complex Life is Uncommon in the Universe,’ by Peter D. Ward and Donald Brownlee (2000)

If it makes you anxious to think that there are other forms of life out there somewhere, this is for you. Ward and Brownlee, two prominent scientists, argue in this 2000 book that it’s highly unlikely that the conditions that led to life on Earth can exist elsewhere. Using research from the fields of astronomy, geology and paleontology, they point to the Earth’s composition and stability as being extremely rare. As an article in The Times assessing the book’s argument put it, “Most everywhere else, the radiation levels are too high, the right chemical elements too rare in abundance, the hospitable planets too few in number and the rain of killer rocks too intense for life ever to have evolved into advanced communities.” Phew!