A Dark Patch on Mars Is Growing

A dark feature of volcanic material on Mars has expanded over a 50-year observation period, according to imagery from multiple orbiters. The cause of the expansion, observed in the Utopia Planitia region, remains uncertain, with scientists proposing wind-related explanations.

Observed Changes

A dark feature in Mars' Utopia Planitia, first photographed by NASA's Viking probes in 1976, has expanded southward over subsequent decades. New images from the European Space Agency's Mars Express orbiter, captured in 2024, show sections of the patch's southern boundary have moved at least 200 miles (320 kilometers) farther south since the initial observations.

This movement suggests an average expansion rate of approximately 4 miles (6.5 kilometers) per year.

Composition and Origin

The dark patch consists of ash and volcanic rocks, including minerals like olivine and pyroxene. This material originated from volcanic eruptions that occurred millions of years ago.

Possible Explanations for Expansion

Scientists from the European Space Agency have proposed two hypotheses for the feature's spread over the past 50 years:

• Martian winds have physically moved the dark ash and volcanic material.
• Lighter-colored surface dust, which previously covered the dark ash, has been blown away by wind, revealing more of the underlying dark material.

The agency has stated there is currently no evidence to determine which hypothesis is correct. Scientists are confident, however, that the movement is connected to Martian wind activity, which is known to scour the surface and redistribute material.

Background on Utopia Planitia

Utopia Planitia is a plain in Mars' northern hemisphere, roughly 2,000 miles (3,300 kilometers) wide. The region has been the site of several exploration missions:

• NASA's Viking 2 lander touched down there in 1976 and conducted operations until 1980.
• China's Zhurong rover landed in 2021 and explored the area before ceasing communication in 2023.

Data from the Zhurong mission has led Chinese scientists to suggest the plain was likely once covered by a large ocean, and they have mapped a potential shoreline.

The rover may have also detected clues of a climatic shift in the region around 400,000 years ago. The region's geology includes large ground cracks known as grabens, which could provide clues to past tectonic activity. Researchers also believe significant amounts of buried ice exist beneath the surface.