LIFE ON MARS Are aliens real? All the UFO sightings, evidence on whether extra-terrestrials exist and conspiracy theories
What was the latest believed UFO sighting?
Strange footage has emerged of a mysterious UFO moving and changing shape in the sky over Sweden.
The intriguing footage was captured by baffled motorists inside the city of Gothenburg which sparked rumours of whether the footage is conclusive proof of extra-terrestrial life.
The footage, captured by onlookers travelling in their car, shows an unidentified flying object move through the sky and appear to change shape.
Russian police have reopened a 60-year-old investigation into the mysterious deaths of nine students on a cross-country ski trip, and are linking the deaths to a theory which blames UFOs.
Known as the Dyatlov Pass Incident, the mystery includes a sliced open tent, bodies dressed in underwear in the snow, traces of radiation and a victim missing a tongue, reported ABC.
The lack of explanation for the deaths sparked conspiracy theories including yetis, UFOs and an attack by local native tribes.
How many alien and UFO sightings have there been?
The alien expert reckons there have been more than 100,000 recorded UFO sightings in the past 100-plus years.
And Sam is far from the only believer on our planet.
From an "alien autopsy" video dating back to 1995 to a video of fighter jets apparently chasing a UFO over the M5, there are hundreds of videos which people have claimed to be proof of alien life.
There's even a clip of a UFO supposedly attacking a Taliban compound, as well as "sightings" in Peckham and Warminster.
Most of the videos have been debunked by experts. In the M5 clip, for example, the motorway lorries look like models.
While the Peckham UFOs were "almost certainly Chinese lanterns", former Ministry of Defence UFO investigator Nick Pope told the Sun Online.
He added that "true believers wouldn’t be dissuaded" by evidence the videos are fake.
Meanwhile, popstar Peter Andre claims to have seen "several UFOs" on a family trip to the Nevada desert.
The desert is also the site of America's famous Area 51 - a highly classified military base at the centre of alien conspiracy theories due to scores of of UFO sightings in the area.