While everybody talked about the mysterious square, others highlighted another, perhaps more intriguing mystery found by the Mars Reconnaissance Orbiter. That is the “monoliths” captured on Mars and Phobos.

So, what’s going on here? First off, like the square structure, the images are real photographs taken by a NASA probe visiting an alien world. They are not new either, with the Mars monolith being captured in 2008, and the Phobos monolith being photographed way back in 1998.

This is not the first time the monoliths – a single upright block of stone – have captured the public’s attention, either. In 2009, astronaut Buzz Aldrin caused a stir when he suggested we should attempt to visit the monolith on Phobos, the largest of Mars’s two moons, before heading back to our own.

“We should go boldly where man has not gone before; fly to comets, visit asteroids, visit the moon of Mars,” the second man on the Moon told C-SPAN in 2009. “There’s a monolith there; a very unusual structure on this little potato-shaped object that that goes around Mars once in seven hours. When people find out about that they’re going to say ‘who put that there, who put that there?’. Well uh the universe put it there. If you choose, God put it there.”

While it would be great to visit Phobos for other reasons, the monolith is not as big of a mystery as alien conspiracy theorists would have you believe. Though the large rock certainly stands out from the background, scientists have a pretty good idea how it got there, without invoking ancient Martians pre-empting the plot of 2001: A Space Odyssey.

“In 1998, the Mars Global Surveyor (MGS) spacecraft made four passes by the innermost of the two Martian satellites, Phobos. The fourth pass, made just over 5 years ago on 12 September 1998, offered the Mars Orbiter Camera (MOC) the opportunity to acquire the highest resolution images of the moon, ever,” NASA’s Jet Propulsion Laboratory explains of the image.

“Several large boulders can be seen, including a very large one near the center that is about 85 meters (~280 feet) in diameter. Most of the boulders may have been ejected from the largest impact crater on Phobos, Stickney.”

The Stickney Crater is about 9.7 kilometers (6 miles) wide, taking up around half of the moon’s surface, formed during an impact event in Phobos’s past. The event offers a plausible mechanism for how the “monolith” got there.

Meanwhile, the Mars monolith can also be explained without invoking alien intelligence. 

“There are lots of rectangular boulders on Earth and Mars and other planets,” Alfred McEwen, the principal investigator from the University of Arizona’s HiRISE department said of the find, per the Daily Mail.

“Layering from rock deposition combined with tectonic fractures creates right-angle planes of weakness such that rectangular blocks tend to weather out and separate from the bedrock.”

The rock may also look more rectangular than it actually is, thanks to the low resolution of the image captured from way above in Mars’s orbit.

“When your resolution is too low to fully resolve an object, it tends to look rectangular because the pixels in the image are squares,” Jonathon Hill, research technician and mission planner at the Mars Space Flight Facility at Arizona State University, and processor of many NASA images, explained to Live Science. “Any curve will look like a series of straight lines if you reduce your resolution enough.”

As well as this, there may be a little pareidolia going on, just as with the square structure currently getting a lot of attention in conspiracy theory circles.