A giant 'shadow' has been creeping across Mars for 50 years — and scientists aren't sure why

A massive dark patch lurking within a giant Martian crater has been creeping across the Red Planet's surface since the feature was first spotted 50 years ago, new photos reveal — and scientists are unsure exactly why this is happening.

The shadowy structure is a patch of ground covered with ash and volcanic rocks, such as olivine and pyroxene, from ancient eruptions that occurred millions of years ago, before Mars was considered geologically dead. It is located in Utopia Planitia, a roughly 2,000-mile-wide (3,300 kilometers) plain in Mars' northern hemisphere.

NASA's Viking probes first photographed the blackened ground in 1976, shortly after arriving at the Red Planet. Since then, several photos have shown that this feature is expanding across the surrounding landscape; these include new images from the European Space Agency's (ESA) Mars Express orbiter, which were captured in 2024 and released April 15.

It is unclear how large the shadowy feature is. However, sections of the patch's southern boundary have moved farther south by at least 200 miles (320 km), based on the latest photos from ESA. This suggests the dark terrain has been expanding by around 4 miles (6.5 km) per year.

Scientists are confident that the movement of the dark patch has something to do with Martian winds, which are known to scour the surface and kick up ash and dust.

"The spread of the ash over the last 50 years has two possible explanations: either it has been picked up and moved about by Martian winds, or the ochre dust that previously covered the dark ash has been blown away," ESA representatives wrote in a statement.

However, there is currently no clue as to which hypothesis is correct, they added.

Utopia Planitia

This region of Mars has been of great interest to scientists over the past half century. In 1976, the Viking 2 lander touched down in Utopia Planitia and carried out a series of "biological experiments" until its demise in 1980.

More recently, China's Zhurong rover also touched down there in 2021 and explored the giant plain before going dark in 2023. Chinese scientists have since used the Zhurong data to show that Utopia Planitia was most likely once covered with one of Mars' largest oceans, and they have even mapped out what they think was once a shoreline. The rover also may have detected clues of a surprising "climatic shift" in the region around 400,000 years ago.

Utopia Planitia is home to several large cracks in the ground, known as grabens, which are one of Mars' most unusual features and could also help provide clues to any tectonic activity that once rocked the Red Planet, according to ESA.

In addition, researchers think there is a significant amount of buried ice beneath the region, which could have big implications for the hunt for extraterrestrial life.

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