Did Mars ever have a liquid ocean on its surface?

Yes, scientific evidence strongly suggests ancient Mars had significant liquid water, possibly forming vast oceans or seas during its early history, potentially covering a third of its northern hemisphere.

What evidence supports the idea of an ancient Martian ocean?

Key evidence includes ancient shorelines, vast valley networks carved by flowing water, mineral deposits like hematite and sulfates formed in water, and atmospheric escape rates indicating a wetter past.

Where did all the water go from Mars?

Most of Mars's ancient water is believed to have escaped into space due to its weak magnetic field and solar wind stripping, with a significant portion also frozen underground in polar ice caps and permafrost.

Could there still be liquid water on Mars today?

While large surface oceans are absent, there is strong evidence for subsurface liquid brine reservoirs, particularly beneath the south polar ice cap, and transient briny flows on crater walls.