Mars Was Blue: Scientists Uncover Evidence of Vast Ancient Oceans

Scientists studying Mars have identified new evidence suggesting the planet once hosted a vast ocean, using satellite data to estimate ancient sea levels during the wettest period in Martian history. Researchers from Italy and Switzerland analysed imagery from three Mars orbiters, focusing on Coprates Chasma, a deep canyon within the vast Valles Marineris system. Their work points to a time when liquid water shaped Mars on a planetary scale, offering fresh clues about its ancient climate and habitability. Evidence of an Ancient Martian Ocean The team examined fan-shaped landforms lining the canyon walls. These formations closely resemble river deltas commonly found on Earth. Such structures typically appear where flowing rivers enter stable bodies of water. According to geomorphologist Fritz Schlunegger of the University of Bern, these features strongly indicate rivers once emptied into an ocean. All identified delta like deposits sit between 3,650 and 3,750 metres below Mars’s surface reference level. This consistent elevation allowed scientists to estimate an ancient shoreline. The inferred sea level sits roughly 1,000 metres above the deepest parts of Valles Marineris, suggesting an ocean comparable in size to Earth’s Arctic Ocean. Geologist Ignatius Argadestya, also from the University of Bern, said the findings represent the largest and deepest ancient ocean yet identified on Mars. The researchers believe this ocean covered much of the planet’s northern hemisphere. What the Findings Mean for Mars History The deposits are estimated to be around 3 billion years old. This timing places the ocean later than many previous estimates of Martian surface water. Researchers describe this era as the period with the greatest availability of surface water on Mars. The discovery strengthens the idea that Mars once had a warm and wet climate. Lakes, rivers, and seas likely shaped its surface over extended periods. While Mars is now cold and dry, mounting evidence suggests it once had conditions suitable for life. Scientists remain uncertain how Mars lost so much water. Some may have escaped into space, while some could be trapped underground as ice. Despite this uncertainty, the planet’s watery past appears increasingly clear. Why These Coastlines Matter Now The newly identified coastlines may become key targets for future exploration. On Earth, ancient shorelines preserve signs of early life. Researchers suggest similar regions on Mars could hold chemical or geological traces of primitive organisms. Life emerged relatively quickly once Earth had stable water. This raises the possibility Mars briefly hosted simple life forms. Future missions may focus on these delta regions to search for preserved biosignatures. The study was published in the journal npj Space Exploration. Scientists say the findings refine understanding of Mars’s evolution and help guide where future rovers should search for signs of ancient life.