Key Takeaways

  • There are no official records of aliens visiting Earth, and scientists who suggest this possibility often find themselves mired in controversy.
  • One recent theory suggest that interstellar object Oumuamua may have been a probe sent by alien spacefarers.
  • Most alien efforts look outwards — for example, SETI studies red dwarf stars that may provide suitable conditions for life in their solar systems.

Do aliens exist? Fictional space aliens who have visited Earth range from the adorable (E.T. and his magical finger) to the threatening (the ruthless Martians of "The War of the Worlds") to the helpful (mighty Superman was from another planet, as we sometimes forget).

Moreover, have aliens visited Earth? Whether extraterrestrial life has actually touched the soil of Earth — or floated above it, observing us all — has been a burning question for almost as long as humankind could look at the stars. The many claims of alien sightings, often buttressed by grainy photos of UFOs, and the many theories about outer space creatures already living among us could fill enough books to weigh down a spacecraft that's collecting samples of our planet.

One thing is for certain: The public and private agencies that deal with all things space focus on finding life away from Earth. They are not researching, at least publicly, the scientific possibility of whether aliens have already been on our planet. For that matter, governments answer stories of UFO sightings on Earth by pointing to the weather or by saying the claim couldn't be corroborated. There are no official records of aliens visiting Earth.

Have Aliens Visited Earth?

Discussion about aliens on Earth can be, for the sake of argument, placed into two camps: claims and theories. Claims are those that appear on the covers of supermarket tabloids or occasionally make for a fun feature in a mainstream news publication. For instance, a New Hampshire couple that spoke of being captured by aliens on a late-summer evening in 1961 as they drove through the White Mountains is the first widely-publicized alien abduction claim, a tale that started a legion of others.

Theories of alien visits can also spread like wildfire in the mainstream news if they are made by someone with authority. It happened only recently. Avi Loeb, the chair of Harvard University's astronomy department, didn't propose that aliens were even close to Earth. Rather, he and a colleague posited that Oumuamua, a cigar-shaped comet or object that whizzed by the sun in 2017, might have been a probe sent to the vicinity of Earth by an alien civilization. The theory, published in The Astrophysical Journal Letters, elicited some derision from scientists.

The minor controversy led NASA physicist Silvano Colombano to say that scientists essentially rock the establishment when they theorize about extraterrestrial life. "General avoidance of the subject by the scientific community" creates a catch-22, Colombano told Quartz. He means that scientists might appear crazy for posing questions about aliens, but society will never know about alien life or any possible alien missions to Earth if no one in the scientific community examines the concept.

Colombano himself got caught up in the debate last year, when Fox News reported he claimed aliens have indeed come to Earth, pointing to a document of his on the space agency's website. But Colombano was quick to correct the Fox News story, saying it was taken out of context and that he believes an alien visit is only theoretically possible. "My perspective was simply that reports of unidentified aerial phenomena should be the object of serious study, even if the chance of identification of some alien technology is very small," he told Live Science.

The Search for Alien Life Looks Outward to Space

The existence of alien life is indeed under serious study, but all eyes and ears on that front are pointed outward, beyond the terra firma of Earth. SETI — the Search for Extra-Terrestrial Intelligence Institute — employs more than 130 scientists, educators and administrative staff in a quest to "explore, understand, and explain the origin and nature of life in the universe and the evolution of intelligence."

SETI projects include using a telescope array to study red dwarf stars that show characteristics indicating the possibility of support for intelligent life. The Allen Telescope Array (ATA) is also examining newly-discovered exoplanets that are found in their star's habitable zone. And SETI is developing a system to search for laser flashes that extraterrestrial societies might use to signal their presence.

SETI's work continues despite occasional hesitations. This year, a research group that included a NASA astrobiologist offered that while the "search for habitable environments and life beyond our solar system is a deeply compelling scientific goal," a large number of planets that were believed to possibly support life actually have unsuitable environments, shrinking the zone of areas where extraterrestrials could survive.

So, do aliens exist? Many scientists believe that humans need to work even harder to determine whether there is extraterrestrial life out there, let alone whether or not aliens have visited Earth. As astronomer and SETI co-founder Jill Tarter once said, because of the vastness of space, our efforts have only amounted to the equivalent of scooping a single glass of water from the ocean.

One of the biggest problems with alien investigations? The luminosity of other stars blocks our view of their planets. See how Starshade is helping scientists get a better look.