The UFO reports piquing Nasa's interest

It was just a normal day's flying for Alex Dietrich – until it wasn't. Streaking through the sky over the tranquil expanse of the Pacific Ocean near San Diego, the US Navy lieutenant commander was taking her F/A-18F Super Hornet fighter jet on a training mission with a colleague in another plane. Then came a voice through the crackle of the radio.

It was an operations officer aboard the warship USS Princeton, asking them to investigate a suspicious object flitting around: on several occasions, it had been spotted 80,000ft (24.2km) high, before suddenly dropping close to the sea and apparently vanishing. 

When the two jets arrived at its last known location, close to the ocean's surface, the water seemed almost to be boiling. Moments later Dietrich saw it: what seemed to be a whitish, oblong object around 40ft (12m) long, hovering just above the water – like a wingless capsule, which she described as resembling a Tic Tac. As they edged in closer, it was gone, accelerating off into the sky at what seemed an impossible speed, leaving a glassy expanse of regular sea behind.

This was the infamous "Tic Tac" incident of 2004, which later went viral when a video captured by advanced tracking equipment on one of the planes was leaked to the New York Times. In the footage, eventually confirmed to be authentic by the US Department of Defense, the object can be seen as an oblong shadow against a bright sky, before suddenly lurching off-camera to the left at uncanny speed.

It's just one of hundreds of peculiar incidents that have made it into the hands of serious officials in recent years. First there was the US government's 2021 assessment of UFOs – which have been rebranded, rather disappointingly, as the more sober-sounding "Unidentified Aerial Phenomena" (UAPs). Now Nasa is expected to release the results of its first-ever study into Unidentified Anomalous Phenomena – their own twist on the historically dubious designation – and the US Congress subcommittee on National Security, the Border and Foreign Affairs is holding a hearing on them.

Around 76 years into America's obsession with aliens – during which the nation has been gripped by reports of flying saucers, weird lights, and the mysteries of Area 51 – the scientific community is finally taking charge. But how do you sift the fancies of conspiracy theories from incidents worthy of investigation? What hallmarks separate a genuine anomaly from a curiously shaped cloud or Chinese balloon? And why are researchers finally paying attention?

A telling pattern

In the summer of 1947, a strange new kind of hysteria swept across the US. From California to Maine, and Michigan to Texas, people began reporting sightings of unusually-shaped objects with a characteristically flat, disc-like appearance in the sky.

It all began with an aviator and businessman from Idaho. Kenneth Arnold had been searching for a downed military aircraft in his single-engine CallAir A-2 one June afternoon, when he saw a bright flash at 10,000ft (3,048m), over the Cascade Mountains in Washington. Nine objects, like giant reflective "pie-pans", were flipping, banking, and weaving in and out of formation in the sky. Arnold watched them zip from one peak to another and calculated that they must have been moving at an incredible speed – around 1,200mph (1,931km/h), more than twice as fast as the record-holder at the time. This was the beginning of America's fascination with the flying saucer.

Before that moment, there were zero mentions of flying saucers in the Earth's atmosphere in any US newspaper since records began in 1770, based on the US Library of Congress newspaper archives. But within a month of Arnold's report, there had been tens of sightings across the country – and what had initially been dismissed as a "tall story" by experts started to cause a national panic.

This is the first challenge of analysing UAPs – the more we look for them or even think about them, the more we seem to spot.

Take the recent Covid-19 pandemic. When scientists looked at the number of UAP sightings across the US, they found major spikes during local lockdowns, when people were confined to their homes. Perhaps people were simply spending more time outside, gazing at the sky. But the researchers also propose another explanation – that the increases were the direct result of people devoting more of their attention to them.

This idea is backed up by the finding that the sighting increases began gradually after each lockdown, suggesting that interest built up in the absence of other activities. It also fits with the finding that UAP sightings follow other macroeconomic trends, such as recessions. We're simply more likely to ponder these suspicious objects when we're in need of distraction, or just plain bored.

Meanwhile, the 2022 assessment of UAPs from the US government revealed that there has been a dramatic increase in the number of sightings since the first iteration emerged in 2021 – with more than 350 received from pilots and other personnel in just one year, compared to 144 for the entire 17-year period covered by the initial report. In fact, some commentators have observed "a new age of UFO mania". 

A shift in perspective

However, very few UAPs turn out to be truly abnormal. Of the roughly 800 sightings Nasa are investigating, so far just 2-5% remain unexplained. According to David Spergel, president of the Simons Foundation and the chair of Nasa's as-yet-unpublished UAP study, many are easily sorted into two categories.

The first are everyday objects and events that can be identified as balloons, drones, atmospheric phenomenon, and anomalies within the camera itself. Whenever Spergel hears of a suspicious incident involving flashing lights, he knows it is overwhelmingly likely to be caused by airplanes. "We only put flashing lights on things that we want to be seen. So when the Ukrainians are attacking Russian trenches or the Russians are attacking Ukrainian cities, they do not put flashing lights on their drones, nor on their military planes," he says.

Why are some people obsessed with UFOs?

The second category is demonstrated by a blunder that befell the British astronaut Tim Peake in 2015. He was staring out of one of the portholes on a 186-day trip aboard the International Space Station (ISS) when he noticed lights moving in formation. First he saw three, then four… he was, he later recalled on a BBC chat show, "perplexed" – believing that he was witnessing alien spaceships.

A MYSTERY SIGNAL

It started in 1998. Scientists at the Parkes Observatory in New South Wales, Australia, noticed interference with their telescope – strange, unexplained radio bursts were emanating from the surrounding atmosphere. Something odd was happening, and it continued for the next 17 years. Then one day, they finally upgraded their interference-monitoring equipment. (Find out what happened in the next box…)

However, Peake soon realised that he wasn't looking at distant objects after all, but tiny droplets. They were Russian urine, which was leaking out of a nearby probe vehicle – where it would have been recycled back into drinking water – and freezing instantly into light-reflecting crystals.

Often, the ordinary is transformed into the intriguing through simple optical illusions, such as the reality-shifting power of perspective, as happened with Peake. This can easily morph the planet Venus – which is almost as big as Earth, but 70 million kilometres (44 million miles) away – into a flying space-object. Similarly, tiny bits of "space dandruff", from crystallised water to flakes of insulation (such as those spotted outside the ISS in another incident one day), have previously been mistaken for extraterrestrial intruders approaching on the horizon.

However, without a second image from another camera, it can be extremely difficult to confirm the nature of these objects – you simply don't have enough information to tell if they are small things close-up or larger objects further away. "So, I think the first thing we're doing is recommending that Nasa facilitate the collection and sharing of better-quality data," says Spergel.

Spergel is optimistic about this. "We've got three to four billion cell phones distributed around the planet, they take good pictures, and can record the local time, the GPS position, local magnetic fields, and gravitational fields – a wealth of information," he says. Spergel explains that the ideal scenario is to have an image of an object taken by several cameras at the same time. This would allow researchers to confirm that it really existed – and wasn't conjured up by a defect in your camera's optics – and triangulate the cameras' data to determine its distance, position, and velocity. This is particularly important, because many UAP sightings involve unexplained acceleration. 

"And ideally, if you could complement this with radar data, then you can get multi-wavelength data and learn more about the properties of the object. And again, most of the time, as you get more data, it will turn out to be something conventional. But the exciting possibility is it [could be] something we don't understand," says Spergel.

A suspicious object

In October 2017, astronomers operating the Pan-Starrs1 telescope, an otherworldly white dome nestled among the clouds on mount Halealakalā in Hawaii, noticed something odd. A mysterious object, which later turned out to be either circular pancake or a cigar-shaped, was hurtling along at staggering speed – fast enough to have come from outside our Solar System.

Not only was "Oumuamua" travelling fast to begin with, but it was accelerating: by November, it was travelling at about 85,700mph (38.3km/sec). This was all the more inexplicable because, though comets usually accelerate as they pass the Sun – propelled by vapourised ice that forms its tail – the object didn't have a tail.

Scientists were baffled. Was it just an unusual comet? Or could it be something else? The prominent theoretical physicist Avi Loeb, a professor of science at Harvard University who has since gained a reputation as a controversial "alien-hunter", suggested that it could be a probe sent to Earth by an advanced extraterrestrial civilisation. (Read more from BBC Future about the interstellar objects that visited our Sun and the Loeb's underwater search for an alien meteor.)

Though the current consensus is that Oumuamua was most likely a natural object – a particularly unusual comet – it had all the properties of a bona fide UAP. And yet, it doesn't quite meet Spergel's standards for evidence of an extraterrestrial civilisation. To be genuinely impressed, he would require something that couldn't be explained by our current understanding of how comets or asteroids behave – something super, ultra-fast. 

"If we saw something, [like] an object that comes into the Solar System at half the speed of light, and then slows down, that would be pretty impressive," says Spergel, pointing out that Earth's velocity is only a 10,000th of the speed of light.

Spergel thinks about it in terms of timelines. Most of the stars around our own Solar System are significantly older or younger than our Sun by at least a billion years. Assuming these would take roughly as long as ours did to spawn apes capable of sending themselves into space, the life elsewhere might either resemble complex microorganisms, such as those found in billion-year-old rocks in the Australian outback, or civilisations that are so mind-bogglingly advanced, their technologies would be far beyond our comprehension.

"It's good to think about what [even] 100 million years means. If you showed someone from 1923 conventional tech, planes and cars and things from today, they'd be impressed, but not shocked. If you took someone from the year 1023, they [would] think we were all witches. A thousand years is a big step in technology. And 100 million years is 100,000 steps like that," says Spergel.

A new discovery

Of course, Nasa isn't really expecting to discover evidence of visits by intelligent aliens – though this remains a possibility. Instead, the report is an opportunity to do a kind of sky audit, and investigate what's been happening around the Earth recently. This includes rare weather phenomenon, some of which were little more than tantalising rumours for centuries before they were finally confirmed by scientists.

Take "sprites" – large electric discharges that light up the Earth's upper atmosphere with strange red blobs and streaks, like luminous sky-jellyfish. They form above thunderstorms, and had been reported since 1886 before they were finally captured on camera more than a hundred years later, in 1989. Even today, what causes them remains a mystery.

"There's some really amazing things that people did not believe exist," says Spergel, explaining that scientists were sceptical about sprites, despite anecdotal reports. "It took the development of high-speed cameras before they were believed," he says.

It's not just a matter of curiosity – any aerial phenomena that isn't well-understood can be dangerous for satellites or planes. "One that surprised me is there's a lot of balloons and drones out there. And those numbers, particularly of drones, are going up quickly," says Spergel. "Some of these can pose a hazard to aviation and need to be tracked properly to make sure they don't," he says.  

A PROSAIC EXPLANATION

…In January 2015, scientists at the Parkes Observatory detected a more specific signal. The wavelength was 2.4 GHz, the classic signature emitted by a microwave. The researchers later realised the interference with their telescope only happened when it was pointed in this equipment's direction, and had occurred exclusively during the day, when staff were heating up their lunches. If someone opened the microwave door before it had timed out, it produced a burst of suspicious radio signals. The mystery was solved, with no aliens involved.

To make any progress – whether with strange weather phenomena or reports of possible alien spacecraft – it all comes back to having high-quality data. The days of squinting at grainy footage of possible flying saucers or blurry shots of suspicious objects in the sky may soon finally be over. But Nasa are aware that they urgently need to de-stigmatise the concept of the UAP.

When Dietrich's plane returned to their ship after the Tic Tac incident, her colleague later recalled that everyone on board had already heard the story – and found it extremely funny. Both were eventually swept up in a rush of interview requests that dragged on for years, and became famous for their sighting – though much of the attention was unwanted. This experience is fairly typical.

At Nasa's first public meeting on UAPs, Nicola Fox – associate administrator for the Science Mission Directorate – spoke about how disheartening it was that the study panellists were already receiving online abuse for their research, which hinders scientific progress and discourages others from getting involved in the field.  

"My hope is that one of the outcomes of the study… will [be to] decrease the sense of conspiracy," says Spergel.

Some might argue that this is how it should have been all along. As Kenneth Arnold told the media in June 1947, "If I was running the country and someone reported something unusual, "I'd certainly want to know more about it".

-bbc