Humanity has still yet to find real, concrete, scientifically-supported evidence of extraterrestrial life. We’ve gotten pretty close, and discovered some chemical markers and other indications that might suggest life once existed somewhere other than Earth, but the hunt is still on for indisputable proof. Well, some Mars watchers now believe they’ve found it, and it’s in the form of a “cannonball.”

An oddly-shaped object was captured on camera by the Mars Curiosity rover, lying on the dusty, rocky, red-tinted surface of the planet. It’s a ball, and it looks completely out of place. A bluish-grey orb sitting atop of a sea of red. Alien hunters say it’s a cannonball, launched during an ancient Martian war. NASA, as you might expect, says they’re crazy.

If you haven’t been following the never-ending flow of conspiracy theories related to Mars lately, let me get you caught up: NASA has taken lots of photos of the planet with its various rovers and orbiters, and then releases huge dumps of those images to the public. When that happens, amateur astronomers and alien hunters always find some kind of “evidence” that suggests Mars was once inhabited by an alien civilization. NASA always has an explanation for these sightings, but they fall on deaf ears, and the Mars alien cover-up conspiracy is born anew.

The “cannonball” spotted by Curiosity is yet another hot topic for debate, and conspiracy supporters say there’s no way such an object could exist on the red planet unless some intelligent civilization was responsible for its creation. NASA says that’s all just a bunch of kooky talk.

NASA is all too familiar with the strange spheres, and this isn’t exactly the first time scientists have spotted them on the surface. In fact, they’re so common that NASA has a nickname for them: “blueberries.” According to the space agency, the peculiar objects are the result of a natural phenomenon called concretion, in which minerals gather and harden inside water-soaked rock. Taking bubble-like shapes, they are more resistant to erosion than the surrounding rock, and when that material erodes away, the odd colored spheres are left behind.

Of course, if you already believe that NASA has been hiding evidence of aliens for decades you probably won’t buy that explanation. Some amateur UFO hunters are positive that the spheres are actually cannonballs fired onto Mars from space, and are clear evidence of an ancient alien war that left Mars in the state it’s in today.