A new study published January 7 in npj Space Exploration presents compelling evidence that Mars once hosted an ocean comparable in size to Earth’s Arctic Ocean, approximately three billion years ago. The research offers the most direct geological support to date for the long-debated hypothesis of a large body of water on Mars and strengthens the argument that the planet may have once been habitable.

The study draws upon data collected by multiple space missions, including the European Space Agency’s ExoMars Trace Gas Orbiter and Mars Express, as well as NASA’s Mars Reconnaissance Orbiter. These instruments collectively enable detailed geological analysis of Mars’ surface, acting as a kind of “geological time machine” that allows researchers to reconstruct ancient planetary conditions.

The investigation focused on Valles Marineris, a vast tectonic canyon system spanning about 2,500 miles along the Martian equator. Within this region, scientists analyzed Coprates Chasma—a trough approximately 600 miles long—that exhibits distinctive geologic features resembling fan deltas found on Earth. Fan deltas form when sediment-laden rivers enter standing water bodies, such as oceans or lakes, creating cone-shaped deposits.

The presence of these delta-like structures at a consistent elevation—around 12,000 feet below the Martian reference datum—suggests that they were once formed along the shoreline of an ancient ocean. The researchers mapped this topographic level across a broad region, identifying a continuous and coherent outline indicative of a long-gone sea.

The estimated size of this body of water matches Earth’s Arctic Ocean, which would have covered a significant portion of Mars’ northern hemisphere. Given that Mars is roughly half the diameter of Earth, such an ocean would have occupied a proportionally greater fraction of the planet’s surface than oceans do on Earth.

This study provides stronger evidence than previous efforts by relying on high-resolution imagery and precise topographic mapping rather than indirect inferences alone. The identification of well-preserved delta formations at a uniform elevation supports the existence of a stable shoreline, which is critical for validating past oceanic conditions.

Despite this advancement, the idea that Mars once had large oceans remains controversial, partly due to the extreme age of these features—over 3 billion years—and the subsequent geological processes that may have altered or obscured their original form. However, the team’s detailed reconstruction based on clear geomorphological evidence marks a significant step forward in understanding Martian hydrology.

The findings carry important implications for astrobiology. The presence of extensive liquid water environments during Mars’ early history suggests conditions potentially conducive to life. Water is a fundamental requirement for life as understood on Earth, and its past abundance increases the likelihood that habitable environments existed on Mars.

Nonetheless, this research also underscores the fragility of water on planetary surfaces. As study co-author Ignatius Argadestya notes, the fact that such an ocean no longer exists demonstrates how vulnerable liquid water can be to loss over time—whether through atmospheric escape, climate change, or other processes.

In summary, this study provides robust geological evidence for a large ancient ocean on Mars, based on high-resolution data and the identification of preserved deltaic landforms. The findings contribute substantially to our understanding of Martian environmental history and continue to fuel scientific inquiry into past habitability beyond Earth.

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Filed under: Astronomy,Science News - @ February 4, 2026 8:06 am