It's really hard not to be skeptical about various stories about alients visiting Earth. But what if extraterrestrial guests left some physical evidences of their trips to our planet? There are many strange objects in the world, both enigmatic and man-made, that might make to believe that alien life does exist.

For example a strange piece of machinery was found in coal in Vladivostok, Russia. It resembles a piece of a tooth wheel and according to tests was artificially made 300 million years ago. The thing is the toothed objects was pure aluminum while humans didn’t figure out how to make it until 1825.

Curiously, the mysterious artifact resembles parts that are used in microscopes and other delicate technical devices. Whether it is a part of an UFO or smth else the further tests will show.

Another strange device was found by a hiker named John J. Williams in 1998. He dug up a stone with an electrical component resembling an electrical plug attached to it. The device became famous as Williams Enigmalith. Many believe that it's a hoax, as Williams refuses to break it (but is willing to sell it for $500,000) but geological analysis has apparently determined the stone around it is 100,000 years old. It would mean the device inside can’t possibly be of human creation.

Some extremely puzzling trinkets were left behind by pre-Columbian people, for example small, golden figures that closely resemble modern jet planes. So-called Ancient Aeroplanes have features resembling fighter planes’ wings, stabilizing tails, and even landing gears. Allegedly ancient astronaut believers made model planes with their proportions which could fly. Maybe the Incas were contacted by alians who possessed the advanced technology, UFO enthusiasts say. Once again these beautiful statuettes might just be artistic representations of flying fish, insects or other winged creatures.

In 2012, the Mexican government released a number of Maya artifacts they had been protecting for 80 years as state secrets. These objects were retrieved from an unexplored pyramid that was found under another pyramid in Calakmul, the site of one of the most powerful ancient Maya cities. A government-sanctioned documentary featured a number of these finds, most of which clearly depict UFOs and alien visitors.

Quite interesting, huh? But the release of the documentaries was followed by a strange pattern of fraud. What’s more, there seems to be very little scientific proof of the authenticity of the artifacts, and the pictures that have emerged online are less than concrete evidence. Perhaps the artifacts were cheap fakes manufactured by a local artisan. Perhaps the officials had second thoughts about the documentary and ordered to shut it down.

Now let me treat you to desert - story of the so-called Betz Mystery Sphere. It's a silvery orb, about 20 centimeters (8 inches) in diameter which was found by the Betz family in 1974. They were inspecting the damage caused by a brush fire that had raged across their woodland on Fort George Island, Florida, when came across the object. The sphere was completely smooth except for a strange, elongated triangle symbol. The Betz family took it home and soon found out that it had strange properties.

For example it reacted to guitar strumming by emitting a throbbing sound and a resonance. It could also stop and change directions when pushed across the floor, eventually returning to the person who pushed it. The orb would occasionally emit low-frequency rattling and vibrations, like there was a motor running inside it and seemed to avoid falling at all costs. It could even climb up a slanted table! Even scientists and representatives of the military were impressed by the orb's tricks.

The Navy analyzed the mysterious object and found it was... just an ordinary stainless steel ball. To this day, it’s not entirely clear what the alien sphere is.