The surface of the planet Mars is currently a barren desert, bereft of most traces of liquid water and life. But recently, more intriguing news about the state of water on Mars has been discovered: Scientists have found evidence not just of the presence of abundant liquid water, but of entire oceans on the surface of the planet four billion years ago.
How much water is this, you ask? Enough to cover the surface of the planet with a layer of liquid 140 meters deep, and enough to form an ocean occupying half of the planet’s northern hemisphere. In some places, this ocean could have been as deep as 1600 meters.
The astounding evidence was discovered by scientists working at the European Southern Observatory (ESO)’s Very Large Telescope in Chile, the W. M. Keck Observatory and the NASA Infrared Telescope Facility in Hawaii. It was subsequently published in Science. The scientists discovered the existence of these vast oceans by mapping water isotopologues over a sixyear period.
Water isotopologues are molecules which only differ by their isotopes; in this case, the isotopologue levels the scientists measured were those of H2O and its “heavier” isotope, the semi-heavy deuterium (HDO). HDO is a naturally occurring molecule that also makes up water, but one hydrogen atom has been replaced with deuterium. Though HDO and H2O have many similarities, HDO is notable due to its “heavier” weight, allowing it to evaporate into the atmosphere less easily than regular water. This means that when more water evaporates from a planet’s surface in an area, there is a higher ratio of HDO to H2O in that area.
The scientists’ mappings of H2O and HDO levels showed that their knowledge and models of how much water was lost over the geological life of Mars is still largely unknown. What was intriguing about the scientists’ mappings of H2O and HDO levels and ratios across the planet, however, was that they varied along topography and seasons, though modern Mars is ostensibly a desert.
Low ratios of HDO to H2O were seen at high altitudes on Mars and high ratios at low altitudes, such as basins and depressions. Likewise, lower ratios were perceived in the winter and higher ratios in the spring. Of specific importance to scientists were the ratios near the poles: It is at the poles that water, in the form of ice, is most abundant. In fact, HDO measurements in this region were shown to be seven times higher than water on Earth.
What such high HDO ratios indicate is that Mars lost a large volume of water long ago. This led the scientists to conclude that Mars was covered in much more water than they originally thought; it could have covered up to 19 percent of Mars’ surface.
These new discoveries have vast implications for the prospect of life on Mars. The fact that there was so much water means there was a larger window of time that the planet could have been habitable. It also provides evidence and optimism for the present-day search for liquid water on Mars.
