Pilot Gabe Zeifman has shared his images of the secretive Nevada Test and Training Range (NTTR), more commonly known as Area 51, after a flight on December 25. Mr Zeifman, who is an amateur photographer, flew his small Cessna 150 plane around the Papoose Dry Lake near to the military base.
Area 51 can be seen in some of the images, and some people are commenting on a strange triangular structure inside a hangar.
The object is blurry and it cannot be determined exactly what it is, but it has still got conspiracy theorists’ tongues wagging.
One person wrote on Twitter: “A mystery long triangular object was spotted in an open Area 51 Hangar.
“According to a message board I moderate this could be the top secret giant sleeve of Toblerone the government has been hiding from us for years!”
Another person said: “I love it when governments ‘leave the door open’ for the world to peek at what’s been going on in secret.”
A third said: “I’m surprised they let him get that close. But here’s the thing, even the US government admits UFOs are real.
“They’re probably doing reverse engineering of alien technology at Area 51. I’d bet money on it.”
Area 51 is the popular name for a United States Air Force base at Groom Lake in the Nevada Desert, 85 miles (135km) north of Las Vegas.
What goes on inside is extremely secret, with the public kept away by warning signs and armed guards.
The secrecy surrounding Area 51 has helped fuel many conspiracy theories.
Most famous is the claim the site hosts an alien spacecraft and the bodies of its pilots, after they crashed at Roswell, New Mexico, in 1947.
Area 51 has been used by American aviation authorities since 1955 and is closed off to those without top-level security clearance.
However, the US Government did not even admit the base existed until 2013, in a series of documents released as part of a Freedom of Information request, and it is heavily protected by armed guards.