What do a strangely fading faraway star, an oddly shaped interstellar interloper in the solar system and a curious spate of UFO sightings by members of the U.S. military all have in common?

They are all mysterious, for one thing—eye-catchingly weird, yet still just hazy outlines that let the imagination run wild. All have recently generated headlines as possible signs of life and intelligence beyond Earth, of some mind-bogglingly advanced alien culture revealing its existence at last to our relatively primitive and planetbound civilization. Yet their most salient shared trait so far is the certainty they provoke in most scientists, who insist these developments represent nothing so sensational. Ask a savvy astronomer or physicist about any of these oddities, and they will tell you, as they have time and time before: It’s not aliens. In fact, it’s never aliens.

Far from being close-minded killjoys, most scientists in the “never aliens” camp desperately want to be convinced otherwise. Their default skeptical stance is a prophylactic against the wiles of wishful thinking, a dare to true believers to provide extraordinary evidence in support of extraordinary claims. What is really extraordinary, the skeptics say, is not so much the possibility of extraterrestrial intelligence but rather the notion that its existence nearby or visitation of Earth could be something easily unnoticed or overlooked. If aliens are out there—or even right here—in abundance, particularly ones wildly advanced beyond our state, why would incontrovertible proof of that reality be so annoyingly elusive?

To put it more succinctly, as the nuclear physicist Enrico Fermi did more than a half century ago, “Where are they?” Given a 10-billion-year-old galaxy filled with stars and planets, and an Earth less than half that age, Fermi guessed we are unlikely to be the first technological culture on the galactic stage. If just one spacefaring civilization predated our own in the Milky Way, he calculated, even moving at a very languorous pace it should have had more than enough time to visit, explore and colonize every planetary system in the galaxy.

Ever since, practitioners of the search for extraterrestrial intelligence (SETI) have been brainstorming about why we do not encounter glaringly obvious signposts of an interstellar diaspora: Maybe there are nigh-universal bottlenecks in the odds for the emergence of life, intelligence or high technology, and we are indeed alone. Maybe we are not alone at all, but interstellar travel is so hard that everyone just stays home. Maybe we are being quarantined, and UFOs are dronelike documentarians recording an intergalactic Planet Earth miniseries. Maybe our galaxy is bursting at the seams with alien civilizations, and we simply have not looked hard enough—presuming we are capable of properly looking at all. Even the know-it-alls in the “never aliens” crowd would concede the diversity of possible answers to Fermi’s question says more about our ignorance than our knowledge.

One of Fermi’s SETI-pioneering peers, the physicist Freeman Dyson, once summarized the situation thus: “Our imaginings about the ways that aliens might make themselves detectable are always like stories of black cats in a dark room. If there are any real aliens, they are likely to behave in ways that we never imagined.” Even so, he added, “the failure of one guess does not mean that we should stop looking”—particularly because whatever may keep our skies alien-free would likely keep the rest of the universe free of star-trekking humans as well. Contemplating Fermi’s question is a way of exploring pathways to our possible futures. Finding aliens—or coming up empty in our searches—has profound implications for our own ultimate cosmic fate.

That is something to keep in mind while considering the latest near-hits (or near-misses), detailed below, in the ongoing search for cosmic company.

Dust Busts “Alien Megastructures”

Discovered in archival data from NASA’s Kepler space telescope in 2015 by the Louisiana State University astronomer Tabetha Boyajian, the extreme episodic dimming of “Tabby’s Star,” or “Boyajian’s Star,” inspired speculations it was being engulfed by starlight-absorbing “alien megastructures” (think: a solar power plant the size of a solar system). Those speculations helped Boyajian and colleagues launch a successful Kickstarter project that raised funding for further scrutiny of the star, an effort that jumped into overdrive in May 2017, when the star began another dimming episode. But instead of revealing aliens, those observations—and others from telescopes around the world—found the culprit is probably clouds of submicron-scale dust around the star.

This illustration depicts a hypothetical uneven ring of dust orbiting Tabby’s Star, which is one possible explanation for the star’s mysterious dimming. Credit: NASA and JPL-Caltech

“If these dips were caused by solid, opaque objects, you’d expect them to block light equally at all colors. But we saw that the dips were deeper in blue [light] than they were in the red, which indicates that something more transparent, like dust, is crossing in front of the star,” Boyajian says. “How do we know it’s not solar panels absorbing blue light more efficiently than red light? Well, we don’t, but we do know dust is all over the universe in many different places, and what we now see is what we’d generally expect from dust.” The result mirrors that of another team led by the University of Arizona astronomer Huan Meng, which also flagged dust as the likely cause of the star’s odd behavior in October 2017.

Even so, Jason Wright, an astronomer at The Pennsylvania State University who collaborates with Boyajian on studies of the star, cautions that much more work is needed as dust is not the only remaining explanation. Other possibilities—such as intrinsic fluctuations in the star’s luminosity or even a black hole with a cold and dusty debris disk drifting across our interstellar line of sight—could also still fit the data. In theory, Wright says, even the “aliens” hypothesis is still on the table—although only if their megastructures are improbably adept at mimicking “boring old dust.”

“You don’t want to immediately cry ‘aliens’ like a boy crying wolf every time you see something and don’t understand it,” Wright says. “But with Tabby’s Star that’s not what has happened—she and her team have spent years trying to solve what is a legitimate astrophysical mystery.” The upside of all the public attention, Wright says, is that it has lured many astronomers to work on Tabby’s Star “precisely because all the ‘aliens’ talk annoyed them, and they wanted to find a natural explanation.”

Eavesdropping on ‘Oumuamua

Astronomers spotted the sizeable object now called ‘Oumuamua (Hawaiian for “first messenger”) streaking by Earth last October. They determined by its speed and trajectory it had dive-bombed past our sun from the depths of interstellar space, perhaps after cruising through the void for billions of years. Theorists had long predicted icy comets cast away from other stars would someday be detected passing through our solar system, yet ‘Oumuamua did not act like a comet at all—despite passing blisteringly close to the sun, it never sprouted a cometlike tail of evaporating ice. It did not look like a comet either, appearing under telescopic scrutiny to be shaped like a half-kilometer-long needle—a form unknown among natural solar system objects but often favored by starships in science fiction. Perhaps, some SETI enthusiasts thought, ‘Oumuamua was an active or derelict probe from another civilization.

This artist’s impression of ‘Oumuamua, the first known interstellar visitor to our solar system, highlight’s the object’s bizarre needle-like shape. Credit: ESO/M. Kornmesser

But when SETI-minded astronomers targeted the object with two exquisitely sensitive radio telescopes to eavesdrop for any artificial transmissions, they detected nothing. Other teams using large telescopes discovered ‘Oumuamua’s surface was a very particular shade of red, the same color that common carbon-rich molecules turn after prolonged exposure to harsh radiation.

The most likely conclusion? Despite its strange shape, trajectory and lack of a tail, ‘Oumuamua is just a comet after all, its ice locked away beneath a tarlike crust hardened and desiccated by eons of bombardment by cosmic rays. Its radio silence adds to a handful of other SETI false alarms in recent years.

“We accept that these things being artificial is really the lowest-probability possibility for what they are—our past work guides us in that,” says Andrew Siemion, director of the Berkeley SETI Research Center and leader of one team tuning into ‘Oumuamua. “All of these are going to be natural—until one turns out not to be.”

Clandestine Close Encounters

Late last year The New York Times published a story about a small, secretive program run by the Department of Defense to study new reports from the armed services about encounters with UFOs. The project was officially canceled in 2012, leading its former head to resign and join a private, for-profit company—To the Stars Academy of Arts & Science (TTSA)—dedicated to declassifying and studying the Pentagon’s batches of UFO-related material. The Times story included two short videos of separate UFO encounters captured by aircraft-mounted infrared cameras, and hinted at the existence of a third that has yet to be released. In the first video, from an encounter off the coast of San Diego in 2004, a fighter jet tracks a lozenge-shaped something that seems to zoom off at incredible speed, apparently without generating exhaust plumes or a sonic boom. In the second video, captured by a different fighter jet under undisclosed circumstances, an object surrounded by a “glowing aura” seems to fly tilted against heavy headwinds in defiance of known principles of aerodynamics, accompanied by audible exclamations from the fighter jet’s crew.

Steve Justice, TTSA's aerospace division director and former Lockheed Martin engineer who worked on advanced top secret aircraft for the latter company’s storied “Skunk Works” division, speculates that in both cases such incredible feats of flight could be due to the objects possessing some sort of warp drive. Such an (entirely theoretical) device would somehow allow an object to change mass and inertia at will, and potentially to travel faster than light by “altering the spacetime metric” around itself. Whether aliens are behind the fighter jet encounters is, to him, somewhat immaterial.

“I’m not really interested in the ‘who’ or the ‘what,’ but I’m really interested in the ‘how,’” Justice says. “How could you make a machine fly like that? To remove the effects of aerodynamics, I’d want to create a volume around myself where I was insulated from them, where I could change my orientation without changing direction, where I could accelerate without generating shock waves. Right now when an airplane pulls its nose up in forward flight, it climbs; when it breaks the sound barrier, it makes a sonic boom. But that’s not what we see here.”

With the global proliferation of digital cameras, the capacity to capture close encounters with UFOs is greater than ever before. Yet most strange-looking phenomena in the sky—such as the strange clouds and glowing arc of a Falcon 9 rocket launched in December 2017—have entirely prosaic and obvious explanations. Credit: SpaceX Flickr

Keep Watching the Skies

Skeptics reviewing the videos obtained by TTSA have postulated more prosaic explanations, while bemoaning both the lack of data due to pernicious state secrecy as well as the organization’s potentially problematic profit-seeking motives. (According to the TTSA Web site, a minimum investment of $200 buys you membership in the organization and finances research into “exotic technologies” associated with UFOs that could lead to “revolutionary breakthroughs in propulsion, energy and communication.”) Perhaps the speeding “lozenge” was a new type of missile, launched from a submarine as part of some earthly power’s clandestine technology test. And maybe the tilting, aura-sheathed object was actually a distant conventional aircraft distorted by image-processing firmware and autotracking sensors within the fighter jet’s gun camera.

This latter possibility Justice acknowledges as “entirely plausible”—save for the obvious urgency in the voices of experienced military pilots as they speak of associated radar tracking, which is not shown on the gun camera’s feed. “Maybe it could have been some set of physical and optical aberrations,” Justice says. “But when I put it in context of all the information in the video, that’s less likely to me.”

Of course, military pilots aren’t the only ones with extensive experience looking at objects in the sky—and the equipment to record what they see. Astronomers have that, too—yet they never seem to ever catch UFOs in the viewfinders of their telescopes. Similarly, the increasingly global ubiquity of smartphones should presumably boost the numbers and quality of UFO encounters captured on video (as they have done for rocket launches), but the flood of eerie footage has yet to materialize.

That raises a red flag for Bruce Macintosh, an astronomer at Stanford University. “In general, interesting physical phenomena are only barely significant when first detected. Then, as technology progresses, those detections become more significant,” he says. “But UFO detections have remained marginal for decades; they’ve just gone from being blurry shapes on film cameras to blurry shapes on the digital infrared sensors of fighter jet gun cameras. This, in spite of the fact that the world’s total imaging capacity has expanded by several orders of magnitude in the past 20 years.” To remain so vexingly residual, he says, UFOs would have to become more elusive in lockstep with our increasing ability to detect them—something no natural process would be expected to do.

Hypothetical aliens with advanced technology could do that, of course. “But then you have to ask why they would choose to remain marginally undetectable rather than just being undetectable,” Macintosh says. “Unless they’re taunting us, it’s hard to come up with a coherent explanation.”

Except, of course, for the obvious one: It’s never aliens. Until, perhaps, it is.