New research indicates that Mars may have once been home to a warm, oceanic environment, based on findings from a rover that examined what is thought to be an ancient shoreline.

The data suggests the presence of buried “beach” deposits formed by wave action over eons, raising the possibility that substantial bodies of liquid water existed on the planet long ago.

Exploring Mars Beneath the Surface

These revelations are based on observations made by the Chinese Zhurong rover, which successfully landed in Utopia Planitia in May 2021 and operated for approximately one year.

Employing ground-penetrating radar (GPR), the rover examined layers up to 80 meters (260 feet) below Mars’ surface.

During its journey of 1.9 kilometers (1.2 miles), Zhurong’s radar uncovered thick, sloped layers consistent with materials deposited along a beach, indicating that waves transported sediment at a steady angle.

“These formations don’t resemble sand dunes, impact craters, or lava flows, which led us to consider the possibility of ancient oceans,” stated Michael Manga, a professor of Earth and planetary science at the University of California, Berkeley.

“The orientation of these formations aligns with what would have been an ancient shoreline. Their gradient and alignment further support the theory that a significant ocean was present for an extended period, permitting the accumulation of sand-like deposits.”

Mars Beaches Resemble Earth’s

These layered deposits, detailed in a study published in the journal Proceedings of the National Academy of Sciences, correspond to the wave-driven build-up of sandy materials.

On Earth, similar beach sediments take millions of years to form, suggesting that a Martian ocean—if it indeed existed—must have endured for a considerable length of time.

Moreover, the radar findings indicate that the layers consist of sand-sized particles rather than fine dust, further validating their classification as ancient beach deposits instead of wind-blown dunes.

Significance of Ancient Beaches on Mars

“These findings bolster the argument for past habitability in this particular area of Mars,” remarked Hai Liu, a professor at the School of Civil Engineering and Transportation at Guangzhou University and a member of the Tianwen-1 science team responsible for overseeing Zhurong.

Co-authors of the research noted that the existence of ancient beaches suggests that rivers deposited sediment into a large body of water, indicating that liquid water—free from ice—was indeed present.

“Shorelines are prime locations to search for signs of past life. The earliest life forms on Earth are believed to have emerged near such interfaces of air and shallow water,” explained Benjamin Cardenas, an assistant professor of geosciences at Pennsylvania State University.

While Mars is currently a cold and arid world with a thin atmosphere that makes stable liquid water improbable on its surface, numerous studies suggest that the planet once possessed a thicker atmosphere capable of supporting vast amounts of liquid water.

While some of that water likely escaped into space over billions of years, substantial quantities may still be frozen beneath the Martian crust or contained within mineral matrices.

The Debate Over Martian Shorelines

For years, planetary scientists have debated whether a vast ocean once covered Mars’ northern lowlands. Images captured by NASA’s Viking orbiters in the 1970s revealed formations resembling shorelines encircling much of the northern hemisphere.

However, these alleged shorelines appeared uneven, varying in altitude by up to 10 kilometers, which contrasts starkly with the relatively flat coastlines observed on Earth.

One proposed explanation is that volcanic activity later reshaped Mars’ spin axis and landscape after an ocean had supposedly formed.

“The changing spin axis of Mars influenced its shape. Hence, regions once flat are no longer level,” Manga explained.

The study indicates that the Tharsis volcanic region—home to the grandest volcanoes in the solar system—altered the planet’s rotation, leading to warped elevation levels. Such dynamic forces may have distorted any previously level shoreline.

Buried Beaches on Mars

Zhurong’s Rover Penetrating Radar (RoPeR) provides a new lens through which to detect features that have remained hidden beneath the Martian surface, largely untouched by the erosive forces or asteroid impacts over millions of years.

“The sand on these beaches comes from rivers and is transported by ocean currents, continuously shifting along the beaches due to wave action,” Manga noted.

In essence, the rover has discovered features that one would typically expect to find along a coastline, preserved for billions of years.

Covering these beach deposits is approximately 10 meters (30 feet) of later materials likely originating from dust storms, volcanic ash, and impacts from meteorites.

This overburden has fortuitously protected the beach layers from weathering, thus preserving the evidence of ancient shorelines.

The Significance of Water’s Mystery on Mars

Zhurong’s findings align with other indications of historical water presence on Mars.

NASA’s Curiosity rover has uncovered sedimentary “wave ripples” in Gale Crater, suggesting the existence of an ancient, ice-free lake, while the Perseverance rover has identified a fossilized river delta in Jezero Crater. However, these discoveries indicate lakes rather than seas.

In contrast, Zhurong’s data paints a picture of a much larger body of water, potentially a genuine ocean.

“To generate ripples from waves, you need an ice-free lake. We’re now asserting the existence of an ice-free ocean. Instead of just ripples, we’re observing beaches,” Manga noted, emphasizing the scale of the findings.

Although Zhurong is no longer operational, the results from its one-year mission contribute valuable new insights into the theory that Mars was once home to a significant ocean, complete with wave-shaped beaches.

Future explorations of these ancient shoreline deposits could provide further understanding of how Mars transitioned from a planet with enduring water bodies to the dry world we see today.

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Featured image: An artistic depiction of Mars 3.6 billion years ago, potentially covered by an ocean that reached nearly half the planet. The blue areas indicate ocean depth up to the shoreline of an ancient sea, referred to as Deuteronilus. The orange star marks the Zhurong rover’s landing site, while the yellow star indicates NASA’s Perseverance rover location, which landed shortly before Zhurong. Credit: Robert Citron

The complete study is published in the Proceedings of the National Academy of Sciences (PNAS).

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