This isn't a doorway for Martians. Although the internet erupted on Thursday after a photograph from NASA's Curiosity rover appeared to show an alien door, experts are pretty sure it's just a natural feature of the Martian landscape.
Neil Hodgkins, who has studied the geology of Mars, told Live Science that it looks like natural erosion.
The image was taken with the Mast camera on May 7, and it was released by NASA later in the week.
Several colorized images have been made from the original black-and-white one, including a panorama made by stitching several of the photographs together, as seen on the website of a panoramic photography company.
There is a history of Martian illusions.
Nicholas Mangold of the University of Nantes in France told Live Science in an email that the subject of the image is not a door at all.
He joked that this may show the Martians were small.
The Vice website reported that the internet suggested that it was the space tomb of Jesus, a crib for E.T., or a save-point for a video game.
The real answer is that it is not. The experts say that what looks like a door is in fact a shallow opening caused by natural forces.
So if the door is not a door, what is it?
The door is caused by erosion according to a vice president at the British geoscience firm Searcher.
He told Live Science in an email that the silt beds and harder sandy beds are what stand out.
They may have been deposited 4 billion years ago in a river or a wind-blown dune.
Is there water on Mars?
The images show traces of them inside the door, as the winds have eroded the strata since they were exposed on the surface.
There are several natural vertical fractures in the image, some of which are caused by the way rocks weather on Mars, and the small cave seems to have formed where the vertical fractures intersect with the strata.
He said that a large boulder has fallen out under its weight to create a door-shaped cave.
The culprit is a rock lying on the surface just to the right of the door, which appears to have a smooth vertical edge, possibly because it fell out recently.
The structure of the rock is what created the door of the Mars rover, according to Mangold.
Mangold said that the open box with door appearance was nothing artificial.
Internet speculation has raised the possibility that the small door-shaped cave may have been caused by aMarsquake, which happened late in 2021.
Mangold is cool on the idea that there is no need for big Marsquakes. It is possible that the fractured rock was formed before the rock was exposed, or that it was a result of thermal stress caused by the seasonal variations in temperature on the planet's surface.
"It's a very beautiful fractured outcrop, indeed, and it's a very beautiful fractured outcrop," said Angelo Pio Rossi of Jacobs University. The door-shaped cave is thought to have been created by the visible cracks in the rock.
He said that part of his work is to find analogues of geological structures seen on Mars and similar structures on our own planet.
Marsquakes probably had nothing to do with it, as any block that is isolated by fractures can eventually fall downslope, even if the slope is gentle.
The image illustrates how useful photographs from the Mars rovers can be.
It was originally published on Live Science.
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