Mars May Have Had an Ocean Three Billion Years Ago

New research indicates Mars may have had a liquid ocean on its surface 3 billion years ago even if the surface temperature was freezing. Furthermore, the researchers behind the study say that such an ocean may have been able to remain liquid even if the temperature on the planet’s surface fell below water’s freezing point due to constant water circulation and periodic coastal rainfall.


Near the end of the last century, NASA landed the Spirit and Opportunity rovers on Mars to try to answer once and for all if the red planet had surface water in its past. Along with a number of follow-up missions, some of which are still operational today, those hardy rovers found the first in a string of discoveries that seem to confirm that Mars indeed had a wet past, maybe even with massive surface lakes and rivers.

However, many climate models depicting the time when this surface water may have existed indicate that the conditions for either a wet and warm Mars or a cold and dry Mars don’t measure up. In hopes of rectifying this inconsistency, researchers from the Université Paris-Saclay have conducted new simulations that not only support the wet Mars hypothesis, but actually show how a massive ocean may have survived otherwise freezing conditions to remain liquid on the planet’s surface.


“Discerning the climate of Mars approximately 3 billion years ago is challenging because the surface features do not appear to support either a warm and wet or cold and dry climate during that time,” explains a press release announcing the new simulations. “Frédéric Schmidt and colleagues conducted numerical climate simulations to evaluate whether a third option—a cold and wet climate—may have been plausible.”

After running their simulations, Schmidt and his team found a unique set of circumstances where a liquid ocean could have persisted in the planet’s northern lowland basin even if the global mean temperatures were below the freezing point. That they say, is “because of ocean circulation that could have regionally warmed the surface up to 4.5 °C.”

Furthermore, the simulations showed that in this type of scenario, the planet could also experience “moderate rainfall near the shorelines and in the northern ocean as well as frozen ice sheets in the southern highlands” that would have helped replenish this ocean via a process called glacial flow.

In effect, the circulation of the ocean water and this periodic rainfall could have allowed Mars to maintain a wet surface ocean even in a freezing cold climate, a scenario the researchers describe as both wet and cold.


Although the study authors offer a complex solution to an even more complex problem, their proposed set of conditions is the first to mesh seamlessly with previous climate data, some of which seems to prove a wet Martian past, while others seem to show that the temperatures would make such a wet past particularly difficult.

As is often the case, more data will be needed to determine the set of conditions on Mars so many years ago. However, with numerous science missions still operating on and around the planet, and others planned for later in the decade, this latest study can at least offer future Mars researchers a viable path toward an ancient Martian surface ocean that matches the data already in hand.

Follow and connect with author Christopher Plain on Twitter: @plain_fiction