Mars attack imminent? Alien believers find a cannon on Red Planet's surface

UFO believers say there is more to these NASA images than the space agency wants the public to know. UFO believers say there is more to these NASA images than the space agency wants the public to know. Photo: AFP/Getty Images, Getty Images Photo: AFP/Getty Images, Getty Images Image 1 of / 72 Caption Close Mars attack imminent? Alien believers find a cannon on Red Planet's surface 1 / 72 Back to Gallery

You've got to hand it to the dedicated souls -- both NASA professionals and armchair UFOlogists -- who pore over the stream of images from Mars rover cameras and find interesting stuff.

The latest is something that looks like a small artillery cannon, a barrel mounted on wheels that seems evocative of the U.S. Civil War.

The image was taken July 29 , or Sol 723 in terms of Martian days, by the Curiosity rover's right mastcam. (There's also a left mastcam as well as left and right navcams and left and right hazcams on the front and rear.)

All those cameras are steadily clicking away, sending thousands of images to NASA's Jet Propulsion Laboratory in Pasadena, Calif., based on commands sent by the mission team. Some data is stored on board the two rovers and transmitted to Earth later, according to NASA. The date on each picture is the date it was taken, not the date it was transmitted.

There's also a time stamp on the images, given in UTC (the initials for Coordinated Universal Time in French), similar to Greenwich Mean Time.

Looking at a whole page of thumbnails of the raw images is a tad overwhelming. Yet, the global audience of Mars rover fans continues to scrutinize them with imaginative flair. Look! I found an iguana!

So far, the space agency hasn't weighed in on whether the image might depict a war cannon (they might be too busy laughing).

Other mysterious items spotted in Mars rover photos over the years include a toy boat, traffic light, thigh bone, two dinosaurs in one photo, a dot of light above the Martian hills as well as a shaft of light seeming to emanate from below the planet's surface, a face that is half-human and half-goat and a UFO in the atmosphere above the planet.

Curiosity landed on Mars Aug. 6, 2012. The other Mars rover, Opportunity, landed Jan. 25, 2004, and has amazed scientists by continuing to operate for more than a decade.

Photos: Check out the slideshow above for other oddities seen in images from the Red Planet.