Guardian: A team of researchers led by Geronimo Villanueva of NASA's Goddard Space Flight Center in Greenbelt, Maryland, reports that Mars used to have an ocean that held more than 20 million km3 of water. The team used several IR telescopes to study the Martian atmosphere for six years; they looked specifically at seasonal and regional changes in water molecules. Normal water molecules in the atmosphere are able to escape Mars's gravitational pull, but heavy water molecules, in which one or both hydrogen atoms have been replaced by deuterium, are not. Consequently, the concentration of deuterium in the planet's atmosphere and in ice can be used to infer historical water levels on the planet's surface. According to the researchers' calculations, if Mars were smooth, it would have been inundated to a depth of 137 m. Given its terrain, however, the researchers suggest that the water pooled into an ocean that covered 20% of the planet's surface. As Mars lost its atmosphere, much of its water vaporized and was then lost to space. The remaining water, which is frozen in the polar ice caps, is only 13% of the volume of the ancient ocean.
