New Evidence Suggests Ancient Ocean Once Covered One-Third of Mars

PASADENA, Calif. — Mars may have once looked much more like Earth than the frozen desert it is today. A new study suggests that a vast ocean once covered approximately one-third of the planet’s surface, leaving behind a telltale "bathtub ring" of land known as a coastal shelf. This discovery could settle a long-standing scientific debate regarding just how much liquid water existed on the Red Planet billions of years ago.

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The research, published in the journal Nature, was led by scientists from the California Institute of Technology and the University of Texas at Austin. Researchers used computer simulations to model what Earth would look like if its oceans completely evaporated, identifying the continental shelf as the most enduring geological marker. By applying these findings to data from NASA’s Mars Orbiter Laser Altimeter, the team discovered a similar sloping feature that wraps around the planet's northern hemisphere.

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While previous missions in the 1970s detected what appeared to be shorelines, those markers were often inconsistent in elevation and difficult to verify. The newly proposed coastal shelf is significantly larger—spanning 650 to 1,300 feet wide—making it much more resistant to erosion over billions of years. Experts believe this shelf was formed by ancient river systems carrying sediment into a massive, stable body of water.

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Recent findings from other missions further support the theory. China’s Zhurong rover recently detected evidence of ancient underground beaches in the same northern plains, while data from NASA’s InSight lander suggests there may still be enough water trapped deep underground to fill an entire ocean. Over time, Mars lost the majority of its surface water as its atmosphere thinned, allowing molecules to escape into space.

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The scientific community expects a more definitive answer in the coming years. The European Space Agency’s Rosalind Franklin rover is scheduled to launch in 2028 and will land on Mars in 2030. Equipped with the ability to probe deep into the surface and underground, the rover will specifically investigate the mineralogy and geology of the proposed marine shelf to see if it truly supported an ancient sea.

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Confirming the existence of a Martian ocean would do more than just rewrite history books; it would provide crucial insights into whether Mars was ever capable of hosting life. By understanding how a once warm and wet planet underwent such a catastrophic climate shift, scientists hope to learn more about the long-term stability of planetary environments across the solar system.

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