UFOs exist - but can experts explain where they come from or who's flying them?
That's the question facing top US intelligence and military officials, who are due to release a report this month looking into sightings of strange craft around the world, including by people like US pilots.
It comes after documents and videos have been released showing strange-looking craft moving in unexplained ways - ways that current US planes aren't able to do.
But the investigators aren't focussed on little green men in flying saucers - this is about trying to identify what these craft actually are, who owns them, and why they are flying near to US planes.
It's what UFO really means - Unidentified Flying Objects. But even that name has changed, many experts now call them UAPs: Unexplained Aerial Phenomena.
The report isn't out yet but officials have told US media that it has found no evidence of alien activity - but cannot not rule it out.
The review of 120 incidents is expected to conclude that US technology was not involved in most cases. But beyond that, the report will take no clear view about what the objects might be, officials said.
The full report - due later in June - will examine decades of military intelligence and sightings to see if the unidentified objects are a threat to US airspace.
Senior US politicians - including Marco Rubio who tried to run for President - have spoken out about why the US needs to do something about the sightings.
"I want us to take it seriously and have a process to take it seriously," he told US news channel CBS. "Maybe it has a very simple answer," Rubio said. "Maybe it doesn't."
What is true, and I'm actually being serious here, there's footage and records of objects in the skies, that we don't know exactly what they are.
Even former US President Barack Obama, who has had a lot of access to secret info over the years, commented saying: "We can't explain how they moved, their trajectory. They did not have an easily explainable pattern.
"And so, you know, I think that people still take seriously trying to investigate and figure out what that is."
A UFO does not necessarily mean aliens visiting Earth from other worlds. Compared to flying saucers, UFOs are often revealed to be quite dull things such as weather balloons or drones.
What's worrying the US is the possibility that some of the flying objects could be spying aircraft belonging to other countries, such as China or Russia.
If that's the case it would represent a serious military concern for the United States and could mean that other countries are much further ahead in terms of engineering and tech.
In the 1950s, as the human race sent probes and then people into orbit, the public fascination with space also sky rocketed.
That fascination was also reflected in popular culture at the time with sci-fi stories often seen in books, television and films.
If humans could visit other planets, people wondered whether Earth could be visited by extraterrestrials, and reported sightings of UFOs increased.
Following several sightings, the US Air Force did investigate UFOs under a report codenamed: 'Project Blue Book' from 1947 to 1969.
Project Blue Book came to the conclusion that none of the UFOs were flown by aliens or were a threat to US national security.
This latest report, which is expected to be released sometime during June 2021, is expected to recommend more UFO research.
The US Congress passed legislation in December, meaning the Department of Defence had to produce a report about "Unidentified Aerial Phenomena" (UPAs) - within six months.
The report has had a lot of attention online and its release will follow several videos of possible UFO sightings.
Most recently a viral video published in May 2021 claimed to show radar footage of unidentified flying objects swarming near to a Navy ship off the coast of San Diego.
That video followed the US Defence Department declassified three videos of UPAs recorded by the Navy, last year.
In one of the videos, fighter pilot, Lt. Commander Alex Dietrich was flying her jet when she saw an unidentified object shaped like a 'tic-tac' mint nearby.
"It was unidentified, and that's why it was so unsettling to us because we weren't expecting it. We couldn't classify it," Dietrich said, explaining that had she not been with other pilots she wouldn't have reported the sighting.
"If I saw this solo, I don't know that I would have come back and said anything - because it sounds so crazy when I say it."
President Donald Trump's former director of national intelligence, John Ratcliffe, told America's Fox News that there was many incidents of "unidentified aerial phenomena", "all over the world".
"And when we talk about sightings, we are talking about objects that have been seen by Navy or Air Force pilots, or have been picked up by satellite imagery, that frankly engage in actions that are difficult to explain, movements that are hard to replicate, that we don't have the technology for," Ratcliffe said.
Meanwhile former president, Donald Trump has also commented, when asked about whether aliens were responsible he said: "I'm not such a believer, but some people are, so I don't want to hurt their dreams or their fears."
The report will not question the existence of UFOs and is unlikely to say that aliens are responsible, but it might not rule them out entirely either.
Let us know what you think in the comments. Are aliens responsible for UFOs?