Several of these tall, shiny pillars have now been found at sites around the globe without warning or explanation since mid-November.
The first was discovered in the US, when a helicopter crew flying over a remote part of a Utah desert counting sheep spotted a strange statue below.
Around the same time as the Utah one vanished, a shiny metal monolith appeared on the other side of the globe in the Romanian hillside.
The structure disappeared several days after it was first spotted near the Petrodava Dacian Fortress, a local archaeological landmark in the northern Neamt country.
Although it is has not been confirmed exactly who is responsible for the monoliths, an anonymous collective called The Most Famous Artist has taken credit for the Utah and California statues, and is selling three replicas for $45,000 (£34,000) each.
However, when asked about the Isle of Wight structure, it said: “The monolith is out of my control at this point. Godspeed to all the aliens working hard around the globe to propagate the myth.”
The structures have sparked comparisons with the movie 2001: A Space Odyssey, where an alien monolith is a recurring symbol that appears to play a role in the development of human evolution.
Bret Hutchings, a helicopter pilot who first spotted the Utah monolith, told local news station KSLTV he thought the structures could be from “a new wave artist” or someone who was a fan of the Stanley Kubrick film.
No one has claimed responsibility for the European monoliths.
Speaking about the Romanian monolith, the Piatra Neamt mayor Andrei Carabelea wrote on Facebook: “There is no reason to panic for those who think there is still life in the universe.”
“My guess is that some alien, cheeky and terrible teenagers left home with their parents’ UFO and started planting metal monoliths around the world,” the mayor said. “First in Utah and then at Piatra Neamt. I am honoured that they chose our city.”
Speculation has also followed the disappearance of the US and Romanian monoliths.
A Colorado photographer told KSTU-TV that he saw four men come to the remote Utah site one night and push over the hollow, stainless steel object, saying “leave no trace” as they walked away.
Officials said the visitors flattened plants with their cars and left behind human waste.
Meanwhile, authorities in the Californian city of Atascadero said its monolith had been torn down by a group of young men that traveled five hours in the middle of the night to remove it.
“We are upset that these young men felt the need to drive five hours to come into our community and vandalise the monolith,” Heather Moreno, the local mayor, said. “The monolith was something unique and fun in an otherwise stressful time.”