Researchers discovered structures known as scarp-fronted deposits, which form when rivers carry sediment into a standing body of water such as an ocean. The deposits lie at similar elevations between about 3,750 and 3,650 metres below Mars’s defined zero level suggesting they once marked an ancient coastline.

By analysing high-resolution images captured by orbiting spacecraft, scientists were able to reconstruct the likely sea level of this ancient Martian ocean. Their calculations indicate the water inside the canyon could have reached depths of around one kilometre in some places.

Reported by BBC, the findings suggest the ancient ocean may have been at least as large as Earth’s Arctic Ocean, extending across much of Mars’s northern hemisphere.

Lead author Ignatius Argadestya said the discovery helps reshape scientists’ understanding of the Red Planet’s past. Although Mars is now cold and dry, the evidence indicates it may once have been a “blue planet” with abundant water.

Scientists say the discovery raises new questions about Mars’s ancient climate and whether the planet might once have supported life. Studying these ancient water-formed landscapes could also help guide future missions searching for signs of past microbial life on Mars.