If we ever found a real cannonball on Mars, it would make us question everything we know about the history of the Red Planet. That transformative moment hasn't happened yet.
NASA's Mars Curiosity rover Twitter account posted an intriguing message on Tuesday highlighting some spherical objects found on the planet:
The Curiosity image shows a delightfully round shape sitting on the dusty surface of Mars. Though the rover first snapped images of the area in late 2016 and early 2017, the photos are receiving renewed attention thanks to a Dec. 2 post on popular alien-theorist blog UFO Sightings Daily, which refers to the round shape as a "cannon ball" about the size of a softball and suggests it is evidence of a war on Mars.
NASA says the sphere is actually less than a quarter inch (5 millimeters) in size and is composed of calcium sulfate, sodium and magnesium.
The tweet also includes an image taken in 2004 by NASA's Opportunity rover, of a collection of spherules known as "blueberries," that shows how round concretions really aren't that odd on Mars. For reference, those hematite-rich spheres are only about the size of BB pellets. Erosion over time left the "blueberries" exposed.
Seeing strange things on Mars has been an entertaining pastime ever since 1976, when NASA's Viking 1 mission revealed a "face on Mars" that the space agency says is really just a regular old mesa. Since then, we've fancifully spotted everything from a " " to an .
This is all a lot of fun, but, as the non-cannonball shows us, everything (so far) has a perfectly mundane explanation.