5 times scientists thought they may have discovered aliens

• Extraterrestrial life could exist, but mysterious objects in the sky aren't evidence of aliens.
• Scientists have thought they were close to discovering alien life a few times — none of it via UFOs.
• Alien close-calls include an object flying through our solar system and signals from the distant cosmos.

Alien theorists have been going wild on the internet, but scientists aren't on board.

As the US discovered a flurry of UFOs — officially called "unidentified anomalous phenomena," or UAPs — in early February, Google searches for "extraterrestrial life" and "are aliens real" spiked. The Associated Press reported that online posts mentioning extraterrestrials increased by nearly 300% after the first object was identified as a balloon from China. Even Elon Musk weighed in with an alien joke.

Most recently, a mysterious giant metal ball washed up on the shores of Japan, inspiring new online rumors.

No scientific research has suggested that any of these mystery objects belong to aliens (though NASA is working on its own framework for assessing UFO incidents). No prominent scientists have come forward to cry "aliens" either.

There have been incidents in the past where some researchers thought they'd come close to discovering signs of alien life — or even extraterrestrial intelligence — but none were UFOs.

Here are the mysteries that have really made scientists think they found aliens.

A radio blast from the cosmos that made alien hunters go 'Wow!'

One of the first deliberate searches for extraterrestrial intelligence nearly struck gold in 1977, when the Big Ear radio telescope at Ohio State University picked up a sudden, strong signal.

It was 30 times louder than the background noise and, unlike natural radio sources like quasars, it only hit one frequency on the radio spectrum.

Astronomer Jerry Ehman first spotted it as he flipped through pages of data, and he made a notation beside the sudden jump in numbers: "Wow!"

Enthusiasts of the Search for Extraterrestrial Intelligence (SETI) speculated that the Wow! signal came from an alien technology. Ehman himself remained skeptical.

Nobody ever heard the Wow! signal again, though astronomers combed the skies to pick it back up. It's still not clear what caused it.

The first interstellar object: Shiny rock, or alien space junk?

In 2017, for the first time ever, astronomers confirmed that an object zipping past the sun had come from beyond our solar system.

They dubbed the first interstellar object 'Oumuamua, which is a Hawaiian term meaning "a messenger from afar arriving first."

The interstellar visitor was shaped like a cigar. It was about 10 times more reflective than asteroids in our solar system. Most curiously, as it zoomed away from the sun, it sped up faster than it should have based on the pure physics of its trajectory.

All this led Avi Loeb, an astrophysicist at Harvard University, to conclude that aliens could have manufactured the object. He published a paper arguing that 'Oumuamua had an "artificial origin," and may have been an adrift, defunct spacecraft from an alien civilization, with a light sail that uses solar energy to accelerate.

Other astronomers argued against his theory, saying that observations of 'Oumuamua are "consistent with a purely natural origin."

A false alarm in the clouds of Venus

The gas phosphine isn't very impressive on Earth, but when scientists found traces of it in the clouds of Venus, it was a big deal.

That's because, on Earth, the garlicky, fish-smelling phosphine comes from microbes. Venus's surface is too hellish to be habitable, but its clouds could be mild enough to harbor communities of microbial life, scientists speculated after the blockbuster study published in the journal Nature Astronomy in 2020.

But that discovery has been mired in controversy after independent reanalysis found issues with the data. NASA tried to confirm the existence of phosphine in Venus's atmosphere, and found none.

Fast, repeating radio signals are still befuddling scientists

Somewhere beyond our galaxy, mysterious entities have been sending out bright bursts of radio waves. They last only a millisecond, and some of them repeat at regular intervals.

These "fast radio bursts," or FRBs, have perplexed scientists since 2007, when the first one was detected.

Though most astronomers who study FRBs believe they have a natural cause, Loeb was once again unafraid to say he thought it was alien technology.

One FRB has been traced back to a magnetar — a dead star with an extremely powerful magnetic field, which causes explosions of energy.

Bubbly Mars dirt hinted at live microbes

Gilbert Levin was an engineer working on a Mars life-detection experiment with NASA's Viking mission in 1976. He wrote in Scientific American in 2019 that he still believes his experiment discovered signs of life on the red planet.

The instrument dunked Mars dirt in a broth and waited for bubbles, which could indicate microbial respiration. It got positive results at both of its test sites near the Viking lander, but the mission failed to detect organic material to support the results.

"The collective general opinion of the large majority of the scientific community does not believe the results of the Viking experiments alone rise to the level of extraordinary evidence," Allard Beutel, a NASA spokesperson, told The Daily Beast in response to Levin's claims in 2019.

He was likely referring to Carl Sagan's famous words, which apply to any potential alien discovery: "Extraordinary claims require extraordinary evidence."