Could this be proof of life on Mars?

NASA's Opportunity Rover has been touring Mars for four years, snapping photos of the planet with its microscopic camera and traveling a total of 25 miles across the dry terrain. Most have been routine but one recent image has stood out against the rest: revealing what appears to be a cross inside of a circle.

The strange and fascinating image could be a several things – like a tiny fossil creature, micro technology or even the impression of a screw head from the rover itself. Or maybe it's evidence of an ancient alien civilization?

Though that scenario is unlikely, Scott Waring of UFO Sightings Daily says the ring around cross also makes it unlikely that the formation was caused by a fossil or micro creature.

"It has very few similarities to crystal, but, again, the ring causes me to rule that one out," Waring wrote on UFO Sightings Daily.

Micro technology likely caused the cross formation, he theorized. These ancient techniques were used to regulate the ecosystem and create a stable, controlled environment. Waring noted that NASA Chief Charles Bolden has said that the Red Planet – though seemingly barren – did have life on it and it may still be there today.

"Mars did have life on it and may still. Ancient micro tech would explain such an advanced world far beyond our own," he said, according to UFO Sightings Daily.

Some observers have theorized the image mimics a Celtic cross, which was used in many ancient cultures before Christianity, UFO Sightings Hotspot reported.

The ring around the cross could represent sun worship and symbolism, making it more aesthetically pleasing. As an Irish legend goes, a Romano-British Christian missionary and bishop in Ireland created the first Celtic cross in the fifth-century by circling a Latin cross to bring it together with the symbol for a pagan moon goddess. Irish Catholics use the symbol to mean eternity and God's endless love.

Some say the mysterious formation around the so-called symbol looks like a sword handle or a wheel, while others have said they can make out the letters "T" and "B" on the cross' corners.

NASA has yet to release an official statement or address the latest bizarre image seen on the planet.

Seeing a Celtic symbol in Mars' rocks isn't the first depiction that some say eerily mirrors Earth. Viewers have also reported seeing traffic lights and cannons on the deserted planet surface. In October, a space journalist named John White was scanning NASA footage and noticed rocks in the corner of the video. He also spotted what appeared to be a 12 - inch long traffic light while he was analyzing the data.

"I posted it on the internet and people said they thought it looked like a set of traffic lights too, although some people did say it looked like a totem pole," White said.

In these instances, NASA said the formations most likely occured when matter hardened and compacted, a process known as Martian concretion, according to the Daily Mail.

Sightings like this often take the form of people spotting religious icons in their food. John Cranfield, of England, says he saw Jesus in his toast on Wednesday. The bred was the only food item he had left at home, and when he pulled it out of the toaster to take a bite, the face of Jesus was etched into the slice. Although his friend Michael, who Cranfield called for a second opinion, said it looks more like Ozzy Osbourne than Jesus, the Inquisitr reported.

Buzzfeed even has a entire article dedicated to 22 people who have claimed to see Jesus in food like Cheetos, a banana chip and pizza. 

There's a name for this seemingly supernatural phenomenon: face pareidolia. When a face is expected, it may trigger a part of the brain responsible for interpreting faces and believing they saw a face, according to the journal Cortex. This theory could explain Cranfield's Jesus sighting, since he said he considers himself a devout Catholic.

But not all episodes of pareidola involve faces, as is the case with White and others who saw images in Mars' rock. Stephanie Pappas of LiveScience stated that this phenomenon is in fact responsible for seeing images on Mars, according to NBC News.