Researchers have mapped an ancient coastline on Mars, revealing a vast ocean comparable to Earth's Arctic Ocean that existed billions of years ago. Using data from orbiting spacecraft, the team identified geological features suggesting long-lasting surface water in the planet's largest canyon. This discovery provides the strongest evidence yet for Mars's watery past.
Geological analysis of Mars indicates the planet once featured rivers and coastlines bordering a massive ocean. A team led by Ignatius Indi and Fritz Schlunegger at the University of Bern in Switzerland examined imagery from NASA's Mars Reconnaissance Orbiter, the European Space Agency's Mars Express, and the ExoMars Trace Gas Orbiter. The ExoMars mission's high-resolution color camera, known as the Bernese Mars, proved crucial for detecting subtle surface differences.
The researchers concentrated on Valles Marineris, a 4,000-kilometer-long equatorial channel, particularly its southeastern Coprates Chasma region, dated to about 3.3 billion years old. By integrating color images with topographic data, they spotted formations resembling Earth's river deltas and mountain-fed lakes. "The Nile delta is a classic example," Schlunegger noted, explaining that similar structures appear where rivers meet seas.
This work traced ancient shorelines, estimating the ocean's extent matched the Arctic Ocean's size, making it Mars's largest. "Our research suggests that around 3 billion years ago, Mars may have hosted long-lasting bodies of surface water inside Valles Marineris, the largest canyon in the Solar System," Indi stated. These waters likely linked to broader northern lowlands.
Prior studies offered indirect hints, such as water-altered minerals and tsunami evidence from asteroid strikes, but definitive proof has been elusive. "The idea that Mars once had large oceans remains controversial – in part because, if they existed, their record is not fresh because they are so old," observed Michael Manga from the University of California, Berkeley.
Ezat Heydari of Jackson State University emphasized the significance: "Oceans on Mars would have acted just like oceans on Earth, and they are vital to the health of the planet." The findings, published in npj Space Exploration, bolster prospects for past life on Mars while underscoring water's fragility.