NASA finds evidence of ancient ocean covering 20 percent of Mars

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The Mars we know today is dry, dusty, and thoroughly inhospitable. It wasn't always like that, though. Evidence is mounting that Mars was a much wetter, more temperate planet a few billion years ago. NASA scientists have just published a paper that explores how much water Mars had and what happened to all of it. According to this analysis, Mars had a gigantic ancient ocean that once covered one-fifth of the planet.

To get a better handle on Mars’ watery past, researchers used the Keck II telescope and NASA’s Infrared Telescope Facility in Hawaii, as well as the ESO’s Very Large Telescope in Chile. They took readings of the Martian atmosphere over six years and analyzed the composition of water in the ice caps. While all water is composed of two hydrogen atoms and one oxygen atom, the specific form of hydrogen can change its properties.

In this case, Mars was found to have a high concentration of so-called “heavy water,” which contains a hydrogen atom with an extra neutron known as deuterium. This makes up a very small proportion of naturally occurring water, so the high ratio of deuterium to regular hydrogen on Mars is very telling.

The Mars of 4.5 billion years ago had an atmosphere, but as the solar wind stripped the envelope of gas away, most of its water would have evaporated into space. However, water with deuterium remains on the surface, and we know the natural ratio of deuterium water to regular water. This allowed the NASA team to estimate how much water Mars had all those eons ago. The findings indicate that only 13 percent of an ancient ocean remains on Mars, mostly in the ice caps.

The original volume of water on Mars would have been enough to cover the entire surface to a depth of 137 meters. Water depth wouldn’t have been the same across the entire planet, of course, but the team did take a look at the topology to see where the water would likely have pooled. It turns out the northern hemisphere of the planet has vast planes that are lower in elevation than the rest of the planet, and the team believes that’s where Mars’ ocean was. This sea probably existed for millions of years and covered 20 percent of the total planet with a maximum depth of nearly one mile.

As we learn more about the evolution of Mars, its habitable phase seems to only get longer. This new data indicates Mars would have been wet for more than a billion years until it finally became the frigid dust ball we know today. That would have been enough time for life to come into being on the Red Planet. Now, we just have to find evidence of it. Curiosity has detected methane in the Martian atmosphere, which might point to ancient biological activity, but could have other explanations as well. The European Space Agency plans to send a mission to Mars in 2018 with the ability to search for the chemical signature of life.

• By Ryan Whitwam on March 6, 2015 at 4:30 pm