Heavy water and the remains of a Martian ocean
By looking at the ice remaining on Mars, NASA scientists were able to determine how much water once covered the planet’s surface. And it looks like it was a considerable amount.
Looking for missing water with infrared
They started by looking at Mars today with infrared telescopes to measure how much ‘heavy’ water present on the planet. Heavy water contains an isotope of hydrogen called deuterium, and is more likely to remain on the planet rather than being lost into the vacuum of space. Once the amount of heavy water was known, they compared it to the amount found in a 4.5 billion-year-old Martian meteorite, then used that ratio to calculate how much normal water must have been already lost.
That amount of water was then plotted over current topographical maps of Mars, revealing that at one time Mars would have had an ocean across the northern hemisphere covering 19 percent of the planet (slightly more than the Atlantic Ocean covers on Earth.) This ocean would have had a maximum depth of 5,000 feet, comparable to the Mediterranean Sea.
So what could such an ocean mean for Mars? One other finding in this study was that the timing and evaporation of all this water would have been considerably slower than previously thought. The red planet would have been ‘wet’ for well over 1.5 billion years, which is longer than it took for life to get started on Earth. So let’s hope Mars made the most of it while it had the chance.
Source: New NASA Findings Suggest Mars Was Once Home To A Giant Ocean by Robbie Gonzalez, io9