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.