Mars's Vanished Ocean: Delta Formations Confirm Vast Water Body

Mars was once not a barren, red desert world but a blue aquatic realm. An international team led by the University of Bern has definitively confirmed the existence of a colossal ocean in the Red Planet's northern hemisphere about three billion years ago—spanning at least the size of Earth's Arctic Ocean—through river delta formations in the Valles Marineris canyon system. This groundbreaking revelation appeared in a study published on January 12, 2026, in npj Space Exploration.

Leveraging ultra-high-resolution imagery from the CaSSIS (Colour and Stereo Surface Imaging System) camera on ESA's ExoMars Trace Gas Orbiter, combined with data from Mars Express and NASA's Mars Reconnaissance Orbiter, scientists scrutinized geomorphic features in the southeast Coprates Chasma. These structures mirror Earth's river deltas: fan-like accumulations of sand and debris plunging straight into standing water, dubbed "fan deltas."

"These images allowed us to examine Mars's terrain with unprecedented precision," states Ignatius Argadestya, Ph.D. candidate at the University of Bern and lead author. By tracing deltas at uniform elevations, the team reconstructed the ancient sea level and pinpointed a clear shoreline. Though wind-carved dunes now blanket them, their pristine shapes endure.

Professor Fritz Schlunegger affirms, "We perceive Mars as arid, yet our evidence paints it as a blue world akin to early Earth." This vast ocean bolsters Mars's habitability prospects, as abundant water could have nurtured life's origins. Next, the team aims to probe the mineral makeup of primordial Martian soils to unravel water's disappearance and erosion dynamics.

This discovery rewrites Martian history and fuels humanity's intrigue with the Red Planet. Future missions might unearth microbial fossils from these primordial seas.