The activity intensified. In April of 2019, the Navy revised its official guidelines for pilots, encouraging them to report U.A.P.s without fear of scorn or censure. In June, Senator Mark Warner, of Virginia, admitted that he had been briefed on the U.A.P. matter. In September, a spokesperson for the Navy announced that the “FLIR1” video, along with two videos associated with sightings off the East Coast in 2015, showed “incursions into our military training ranges by unidentified aerial phenomena.” The “unidentified” label had been given an institutional imprimatur.

The debunkers were unimpressed by the designation, and their work continued apace. Mick West devoted multiple YouTube videos to his contention that “FLIR1” shows, in all likelihood, a distant plane. He maintained that the remainder of the available evidence from the Nimitz encounter was even shakier: he suspects that the presences picked up by the U.S.S. Princeton were probably birds or clouds, registered by a brand-new and likely miscalibrated radar system—the U.S.S. Roosevelt, off the East Coast, had also received a technological upgrade before a similar raft of sightings in 2014 and 2015—and that the Tic Tac-shaped object Commander Fravor saw was something like a target balloon. He has no explanation for what the other pilots saw, but points out that perceptions are subject to illusion, and memory is malleable.

Were our finest pilots and radar operators so inept that they were unable to recognize an airplane in restricted airspace? Or was the government using the word “unidentified” to conceal some deeply classified program that a branch of the service was testing without bothering to notify the Nimitz pilots? The former Pentagon official assured me that West “doesn’t have the whole story. There’s data he will never see—there’s much more that I would include in a classified environment.” He went on, “If Mick West feeds the stigma that allows a potential adversary to fly all over your back yard, then, cool—just because it looks weird, I guess we’ll ignore it.”

The point of using the term “unidentified,” he said, was “to help remove the stigma.” He told me, “At some point, we needed to just admit that there are things in the sky we can’t identify.” Despite the fact that most adults carry around exceptionally good camera technology in their pockets, most U.F.O. photos and videos remain maddeningly indistinct, but the former Pentagon official implied that the government possesses stark visual documentation; Elizondo and Mellon have said the same thing. According to Tim McMillan, in the past two years, the Pentagon’s U.A.P. investigators have distributed two classified intelligence papers, on secure networks, that allegedly contain images and videos of bizarre spectacles, including a cube-shaped object and a large equilateral triangle emerging from the ocean. One report brooked the subject of “alien” or “non-human” technology, but also provided a litany of prosaic possibilities. The former Pentagon official cautioned, “ ‘Unidentified’ doesn’t mean little green men—it just means there’s something there.” He continued, “If it turns out that everything we’ve seen is weather balloons, or a quadcopter designed to look like something else, nobody is going to lose sleep over it.”

In June of 2020, Senator Marco Rubio added text into the 2021 Intelligence Authorization Act requesting—though not requiring—that the director of National Intelligence, along with the Secretary of Defense, produce “a detailed analysis of unidentified aerial phenomena data and intelligence reporting.” This language, which allowed them a hundred and eighty days to produce the report, drew heavily from proposals by Mellon, and it was clear that this concerted effort, at least in theory, was a more productive and more cost-effective iteration of the original vision for AATIP. Mellon told me, “This creates an opening and an opportunity, and now the name of the game is to make sure we don’t miss that open window.”

Still, the former Pentagon official told me, “it wasn’t until August of 2020 that the effort was really real.” That month, the Deputy Secretary of Defense, David Norquist, publicly announced the existence of the Unidentified Aerial Phenomena Task Force, whose report is anticipated in June. The Intelligence Authorization Act finally passed in December. The former Pentagon official worries that an appetite for disclosure has been heedlessly stoked. “The public, I would hope, doesn’t expect to see the crown jewels,” he said.

West was nonchalant. “They’re just U.F.O. fans,” he said of Reid and Rubio. “They’ve been convinced there’s something to it and so are trying to push for disclosure.” The former Pentagon official conceded that there were “a lot of government people who are enthusiasts on the subject who watch the History Channel and eat this stuff up 24/7.” But, he said, the current mood was by no means set by “a small cadre of true believers.”

Virtually all astrobiologists suspect that we are not alone. Seth Shostak, the senior astronomer at the SETI Institute, has wagered that we will find incontrovertible proof of intelligent life by 2036. Astronomers have determined that there may be hundreds of millions of potentially habitable exoplanets in just our galaxy. Interstellar travel by living beings still seems like a wildly remote possibility, but physicists have known since the early nineteen-nineties that faster-than-light travel is possible in theory, and new research has brought this marginally closer to being achievable in practice. These advances—along with the further inference that ours is a mediocre or even inferior civilization, one that could well be millions or billions of years behind our distant neighbors—have lent a bare-bones plausibility to the idea that U.F.O.s have extraterrestrial origins.

Such a prospect, as Hynek wrote in the mid-nineteen-eighties, “overheats the human mental circuits and blows the fuses in a protective mechanism for the mind.” Its destabilizing influence was clear. I would begin interviews with sources who seemed lucid and prudent and who insisted, like Kean, that they were interested only in vetted data, and that they used the term “U.F.O.” in the strictly literal sense—whether the objects were spaceships or drones or clouds, we just didn’t know. An hour later, they would reveal to me that the aliens had been living in secret bases under the ocean for millions of years, had genetically altered primates to become our ancestors, and had taught accounting to the Sumerians.

Since 2017, Kean has covered the U.F.O. beat for the Times, sharing a byline with Ralph Blumenthal on a handful of stories. These have steered clear of such genre mainstays as crop circles and Nazca Lines, but their most recent article, published last July, veered into fringe territory. In it, they referred to “a series of unclassified slides,” of somewhat uncertain lineage but apparently shown at congressional briefings, that mentioned “off-world” vehicles and “crash retrievals.” Kean told me in an uncharacteristically hesitant but nonetheless matter-of-fact way that she had begun to come around to the idea that U.F.O. fragments had been hoarded somewhere. In 2019, Luis Elizondo had suggested to Tucker Carlson that such detritus existed. (He then quickly invoked his security oath.) Kean cited Jacques Vallée, perhaps the most famous living ufologist, and the basis for François Truffaut’s character in “Close Encounters of the Third Kind,” who has been working with Garry Nolan, a Stanford immunologist, to analyze purported crash material for scientific publication. (Vallée declined to speak about it on the record, concerned that it might undermine the peer-review process, but told me, “We hope it will be the first U.F.O. case published in a refereed scientific journal.”)

In the story, Kean and Blumenthal wrote that Harry Reid “believed that crashes of vehicles from other worlds had occurred and that retrieved materials had been studied secretly for decades, often by aerospace companies under government contracts.” The day after its publication, the Times had to append a correction: Senator Reid did not believe that crash debris had been allocated to private military contractors for study; he believed that U.F.O.s may have crashed, and that, if so, we should be studying the fallout. When I asked Reid about the confusion, he told me that he admired Kean but that he had never seen proof of any remnants—something Kean had never actually claimed. He left no doubt in our conversation as to his personal assessment. “I was told for decades that Lockheed had some of these retrieved materials,” he said. “And I tried to get, as I recall, a classified approval by the Pentagon to have me go look at the stuff. They would not approve that. I don’t know what all the numbers were, what kind of classification it was, but they would not give that to me.” He told me that the Pentagon had not provided a reason. I asked if that was why he’d requested SAP status for AATIP. He said, “Yeah, that’s why I wanted them to take a look at it. But they wouldn’t give me the clearance.” (A representative of Lockheed Martin declined to comment for this article.)

The former Pentagon official told me that he found Kean’s evidence wanting. “There are terms in Leslie’s slides that we don’t use—stuff we would never say,” he said. “It doesn’t pass the smell test.” But, when I asked him whether he thought that there might be recovered debris somewhere, he paused for a surprisingly long time. He finally said, “I couldn’t say yes, like Lue”—Luis Elizondo—“did. I honestly don’t know.” He continued, “There are guys who spent their lives studying stuff like Roswell and died with no answers. Are we all going to die with no answers?”

Not everyone needs answers, or expects the government to provide them. In February, I spoke to Vincent Aiello, a podcaster and former fighter pilot, who served on the Nimitz at the time of the encounter. He told me that the widespread impression of Commander Fravor’s story back then, thirteen years before it became a news sensation, was that it sounded pretty far out, but that the gossip and laughter on the ship petered out after a day or two. “Most military aviators have a job to do and they do it well,” he said. “Why pursue life’s great mysteries when that’s what Geraldo Rivera is for?”

The mysteries have shown no signs of abatement. In early April, the eminent U.F.O. journalist George Knapp, along with the documentary filmmaker Jeremy Kenyon Lockyer Corbell, best known for his participation in an ill-begotten crusade to “storm” Nevada’s Area 51, released a video and a series of photos that had apparently been leaked from the U.A.P. Task Force’s classified intelligence reports. The video, taken with night-vision goggles, shows three airborne triangles, intermittently flashing with eerie incandescence as they rotate against a starry sky. Kean texted me, “Breaking huge story.” She was trying to get to the bottom of the video, but doubted that any of her sources would be willing to authenticate something so hot. The next day, the Department of Defense confirmed that the video was real and said that it had been taken by Navy personnel. Mick West argued, persuasively, that the pyramids were an airplane and two stars, distorted by a lens artifact. Kean, for her part, told me that she was “only just starting to look into the situation,” but volunteered that West was “being reasonable.” The Pentagon refused further comment.

The object he’d encountered was about forty feet long, disobeyed the principles of aerodynamics as he understood them, and looked exactly like a giant Tic Tac. “When Commander Fravor’s story came out in the New York Times, all my buddies had a jaw-drop moment. Even my old boss called me up and said, ‘I read about the Nimitz, and I wanted to say I’m so sorry I called you an idiot.’ ” ♦

An earlier version of this article misidentified the author of the reporting on Skinwalker Ranch and the Web site where it was published.