A strange light that hovered over the St. Louis Gateway Arch this week is sparking plenty of debate on the internet.

Surveillance footage recorded at Malcolm W Martin Memorial Park on Tuesday and posted to Facebook shows the mysterious object hovering over the famous arch. “We guarantee you will be perplexed if you watch all 5 minutes of this surveillance footage!” explained the Park, in a post on its Facebook page. The video has been viewed 615,000 times.

Possible explanations for the light suggested by commenters on Facebook include a drone with a unidirectional light or a Chinese lantern.

Fox 2 News also received video footage of the odd light from Chase Rhoads, who said that he saw something strange over the arch early Tuesday morning. Scott Air Force Base said there was nothing out of the ordinary to report when contacted by Fox 2 News, and a spokesman for the National Park Service said there were no reports of anything strange on Tuesday.

This is not the first time that a mysterious object has been spotted near the St. Louis landmark. Video from the same camera at Malcolm W. Martin Memorial Park also captured an unexplained object that appeared in broad daylight on July 14 2016.

Earlier this year video of a mysterious object near a military base in Dayton, Ohio, also had the internet buzzing.

Last month, a strange, apparently burning object was spotted in the sky over parts of the western U.S. , generating plenty of chatter on social media. The object was later identified as a Chinese rocket burning up on re-entry into the Earth’s atmosphere.

In January the CIA offered a peek into its ‘X-files,’ shining a spotlight on a series of once-classified UFO documents. The UFO documents, which date primarily from the 1940s and 1950s, are among hundreds that the CIA declassified in 1978.

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