How first contact with aliens would most likely happen, and how we'd know it's real

"First contact" with aliens could take very different forms, and each is checked differently:

An artificial signal would look unlike anything nature makes: an extremely narrow transmission, a hertz or so wide, that shows up only when the telescope points at one star and vanishes when it looks away. Optical searches look for laser pulses lasting billionths of a second. The largest project, Breakthrough Listen, launched in 2015 with $100 million over ten years to survey the million nearest stars and 100 galaxies. According to a July 2026 paper, South Africa's MeerKAT array alone has made more than 1.2 million pointings since 2022 with "no confirmed detection of a technosignature." The SETI Institute meanwhile is expanding a network of cameras that watch for laser flashes, now at five sites.

This is the kind of claim that can be checked fastest. The SETI Institute calls a confirming observation at another radio telescope the key test, and its Project Phoenix could follow up "within minutes" with two widely separated telescopes. But history shows how messy it gets. When the first pulsar turned up in 1967 it took about three months to show it was a star, and Antony Hewish, who shared a Nobel Prize for the discovery, recalled that "we had to face the possibility that the signals were" artificial. The 2019 candidate BLC1 was ruled out only after two and a half years, and the 1977 Wow! signal never came back. Details are in our SETI signal tracker.

If a signal were confirmed, a harder stage would begin: working out what, if anything, it says. More in how we would talk to aliens.

A civilization doesn't have to broadcast to be found. A "Dyson sphere," a giant structure harvesting a star's light, should glow in the infrared. In 2024 Project Hephaistos sifted about five million sources within roughly 1,000 light-years and came up with seven candidates. Within weeks other researchers suggested dusty background galaxies could mimic the signal, and in July 2026 a team using the James Webb Space Telescope checked two of the seven and concluded, in a paper not yet peer-reviewed, that "the infrared excess does not originate from Dysonian megastructures." Two years, and two candidates gone.

Another approach is to look in planetary atmospheres for pollution only industry makes, such as nitrogen dioxide or CFCs. It is possible in principle but hard: a 2021 study estimated that a future 15-meter space telescope would need about 400 hours to detect Earth-level nitrogen dioxide pollution about 33 light-years away. Some scientists, such as Penn State's Jason Wright, argue that technosignatures could be more abundant, longer-lived and less ambiguous than biosignatures.

This is how most scientists expect the first discovery to come, and where the arguments last longest. In April 2025 a Cambridge-led team reported signs of the gas DMS, made on Earth mostly by marine life, on the planet K2-18b, at "3 sigma," well short of the 5 sigma a discovery needs. Reanalyses by other teams didn't support it, and in September 2026 even the original team wrote that "more observations are required."

In September 2025 NASA announced a potential biosignature in the "Cheyava Falls" rock examined by the Perseverance rover on Mars. Acting NASA Administrator Sean Duffy called it "the closest we have ever come to discovering life on Mars," while the scientists warned that such a claim requires extraordinary evidence. Testing the rock in a lab means bringing it to Earth, and Congress did not fund NASA's Mars Sample Return program in its 2026 budget. China plans to return Martian samples around 2031.

History counsels patience. The Viking lander's life-detection experiment on Mars in 1976 gave a "positive" result that is still argued over 50 years later. The organic compounds in the Martian meteorite ALH84001, presented in 1996 as evidence of life, were explained in 2022 by chemistry without life. NASA scientists even proposed a seven-level scale in 2021, CoLD (Confidence of Life Detection), from a signal known to come from biology up to follow-up observations confirming predicted biological behavior. A real discovery would climb it step by step, over years.

Three objects from other stars have already passed through the solar system: 'Oumuamua (2017), comet Borisov (2019) and 3I/ATLAS (2025). Harvard astrophysicist Avi Loeb asked whether the first and third were artificial, and both times science found a natural explanation. A 2023 paper in Nature explained 'Oumuamua's odd acceleration with hydrogen escaping from its ice, and NASA concluded that "3I/ATLAS is a comet." In 2026 the Webb telescope found methane in it, and enough deuterium to suggest it may have formed 10 to 12 billion years ago.

What would make such an object truly suspicious? Acceleration with no gas to explain it, a radio transmission, a deliberate change of course, or a makeup with no natural explanation. The Vera C. Rubin Observatory in Chile, which began its main survey in June 2026, should find more of them, with estimates ranging from one or two a year to dozens. ESA's Comet Interceptor, due to launch in late 2028 or early 2029, will wait in space for a chance to fly to a fresh comet or interstellar object. Checking such an object is relatively quick, weeks to months while it is visible, but there is usually no way to reach it.

This is the movie scenario, and so far it has no evidence. The Pentagon's AARO wrote in its 2024 annual report that it had "discovered no evidence of extraterrestrial beings, activity, or technology." Its July 2026 report said every case it resolved turned out to be ordinary, and that no evidence suggests any US government or private entity has ever captured UAP-derived materials. NASA's expert panel found in 2023 "no reason to conclude that existing UAP reports have an extraterrestrial source." The PURSUE files the Department of War has released since May 2026 are, by definition, cases the government could not resolve.

What would count as evidence? Physical material tested by independent labs, multi-sensor data published in full, and many independent witnesses. There is no scientific protocol for this scenario either: the SETI protocol covers signals from space, while UFOs in Earth's skies are a matter for militaries and governments. What officials have actually said is in our tracker, and how to check a viral clip is in our UFO video guide.

In a survey published in Nature Astronomy in January 2025, led by Durham University philosopher Peter Vickers, 86.6% of the astrobiologists who took part agreed that basic life probably exists elsewhere in the universe. For complex life the figure was 67.4%, and for intelligent life just 58.2%. In follow-up surveys taken right after each candidate was announced, published in 2026, only 6.6% agreed that life had probably been found on K2-18b, and 15.1% for the Martian rock.

Predictions point to microbes too, not ships. NASA's chief scientist Ellen Stofan said in 2015: "I think we're going to have strong indications of life beyond Earth within a decade, and I think we're going to have definitive evidence within 20 to 30 years," adding, "We are not talking about little green men. We are talking about little microbes." The decade passed without an accepted detection. The SETI Institute's Seth Shostak told Congress in 2014 there were "three horses in a race": life in the solar system, gases in exoplanet atmospheres, and signals. Who else has predicted contact, and when, is in our predictions scoreboard.

It almost certainly wouldn't start with a surprise press conference. More likely with a rumor, a preprint or one observatory asking another to check something. The International Academy of Astronautics' declaration, updated in June 2026, asks for any candidate to be confirmed by several independent facilities before an announcement. As Michael Garrett, who led the update, put it: "We do not shout 'alien' the moment we see a strange blip." What would follow an announcement is in our first contact protocol guide.