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This Mars Optical Illusion Is Tripping Me Out: Pit or Plateau?

It's a pit, but my mind doesn't want to see it that way.

Black-and-white overhead view of Mars landscape with a heavily shadowed elongated pit.
What do you see? A plateau or a pit? This is an elongated pit that collapsed in a fractured area of Mars. Note the smaller pit toward the bottom as well.
NASA/JPL/UArizona

This story is part of Welcome to Mars, our series exploring the red planet.

Whoa, dude. My eyes and brain are facing a fun challenge with an image from NASA's Mars Reconnaissance Orbiter spacecraft. The HiRise camera team at the University of Arizona shared a view on Monday of a landscape in the Ceraunius Fossae area of the red planet. I'm having trouble processing the fact that the highlighted feature goes down, not up. 

The HiRise team said we're looking at "an elongated collapse pit." My brain is seeing it as a plateau thanks to the angle and direction of the lighting. It looks to me like a raised scar or a giant space slug. With some effort and concentration, I can get the image to look like a pit, but it inevitably flips back. 

If you easily see this as an indentation, then you're probably wondering what I'm going on about. But if you're like me and tend to see raised areas instead of pits in views like this, then you can try the trick of flipping the image around to see if reorienting the shadow brings it into focus. This works well for me.

Is this any better? Here's the HiRise view of a collapse pit turned upside-down.

NASA/JPL-Caltech/UArizona

HiRise has a good view of the surface, but that leads to some questions as to what might be going on out of sight. "This observation can help to tell whether or not there is a subterranean connection to this pit," said the team. "As an added bonus, the much smaller depression to its south also appears to be another collapse pit."  

NASA doesn't say explicitly how long that big pit is, but based on another image of it with a scale, it seems to be about 3,900 feet (1,200 meters) in length.

If you like this Martian pit, then you'll love these:

Pits on Mars are fascinating and worthy of deeper study. Researchers suspect Mars is hiding some volcanic caves, which could be destinations for future exploration by robots or human visitors looking for signs of ancient life or a sheltered place to camp out on an unfriendly planet.