This Is a Collapsed Pit on Mars, Not a Pimple

Mars has been in the news a lot lately, and for good reason. With the historic landing of the Perseverance Rover earlier in the year, and the successful flight of Ingenuity, the first-ever aircraft to fly in another atmosphere, earlier this morning (April 19, 2021), there’s no shortage of exciting stories of technical brilliance from the human-built wonders exploring the red planet. High above the plucky helicopter, the Mars Reconnaissance Orbiter (MRO) surveys the Martian landscape on a grand scale. A brain-bending image released by High Resolution Imaging Science Experiment (HiRISE), a powerful camera aboard MRO, shows a sunken pit in the planet’s polar region. From the high-altitude perspective of the orbiter, it’s easy for the mind to warp the concave depression into a convex, acne-esque Martian polar zit!

The HiRISE team knows the latitude, longitude, and altitude of MRO for all of their imagery. They see the sun’s angle for the target area, in this case, a low 8° above the horizon. This means that they can use the location of the shadows in the image to determine that the circular pattern in the layered deposits of minerals and ices (likely both water ice AND frozen carbon dioxide) is sunken into the Martian surface. Without this context, it is easy to mistakenly see the object as convex, rising like a whitehead on a red planet.

An Artist’s concept of the Mars Reconnaissance Orbiter above the Martian surface. Credit: NASA

Part of the reason it’s so easy to associate the image with acne is also its color. Like most space-related photography, it is important to dig a little deeper into the nature of the color in this image. HiRISE observes in infrared (IR) and some visible light, but it doesn’t see color the way your eye does. Producing images where the colors seem close to what they would for a human requires processing, stretching, and shifting various wavelengths. The specifics can be seen in this HiRISE document.

A merged image featuring black-and-white data along with IRB (infrared, red, blue) of the collapsed pit. Note the difference from the RGB (red, green, blue) image at the top of this article. Credit: NASA/JPL/University of Arizona

Getting back to the pit image, we can’t help but ask questions. What process formed this pit? Was there a subsurface volume of ice that sublimated away, leaving a void that ultimately collapsed? Was this a gradual process or a sudden event? The true nature of the feature remains a mystery for now. Like so many scientific endeavors, this incredible data leaves us with more questions to explore in the future.

HiRISE has produced countless high-resolution images like this. It even has the capacity to image the Perseverance Rover on the surface of the planet! A fantastic way to spend hours of your time is to explore the nearly endless library of pictures and stories available on the HiRISE website. 

An enhanced color HiRISE image shows the Perseverance Rover on the surface of Mars. Credit: NASA/JPL/University of Arizona

Our continuing exploration of Mars reveals a complex world of various geological processes. We see ongoing activity like Marsquakes, planet-wide dust storms, and even evidence of subsurface lakes! We see evidence of a warm, watery past as well. 

Thanks to programs like MRO, Perseverance, and countless others, we understand our dusty red neighbor world better than we ever have before. No other object in the solar system inspires such curiosity and wonder, and we are lucky to be present during the golden age of Mars exploration. 

Lead Image: A HiRISE image of the southern polar region of Mars shows a sunken pit on the layered surface. Credit: NASA/JPL/University of Arizona

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Ralph Crewe

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