The Sunspot Solar Observatory usually spends its time looking at the Sun and trying to understand our celestial neighbour. But it has been banned from doing so for the past week, since federal agents secretly arrived and shut down the entire area.

Its website only says that the shutdown happened "due to unforeseen circumstances" and that the facility would remain closed "until further notice".

Local police said they had received reports that FBI agents arrived in a Blackhawk helicopter and swooped around the observatory. They would not even tell law enforcement why they were there, police said.

The local sheriff's office said it had no explanation of what had happened, but suggested that there was "a lot of stuff going on".

"The FBI is refusing to tell us what's going on," Otero County Sheriff Benny House told ABC 7.

"We've got people up there (at Sunspot) that requested us to standby while they evacuate it, nobody would really elaborate on any of the circumstances as to why.

"The FBI were up there. What their purpose was nobody will say."

He also described the mysterious scene as the FBI swooped on the facility.

"For the FBI to get involved that quick and be so secretive about it, there was a lot of stuff going on up there.

"There was a Blackhawk helicopter, a bunch of people around antennas and work crews on towers but nobody would tell us anything."

The mystery and the observatory's usual work has led to theories across the internet suggesting the shutdown came after scientists spotted something they shouldn't have. One prominent YouTube channel suggested it had accidentally seen an alien craft, for instance.

Some have noted the fact that the observatory is only around 200km from the famous Roswell landing site. In 1947, a UFO dropped fell down to Earth there that officials say was a weather balloon dropped down in that area – but many claim that something more extraterrestrial actually dropped down to Earth there.

The Independent

More about: Alien