Ancient Mars Had Enough Water For A Giant Ocean

As shown in this computer simulation, 4.5 billion years ago, some 20% of Mars’s surface was blanketed by a water ocean. That’s according to a new study of water molecules in the Red Planet’s atmosphere (Science 2015, DOI: 10.1126/science.aaa3630).

Although scientists have known Mars was once wet, observations have been localized and seasonal, limiting a global perspective of Mars’s water. Now, researchers at NASA Goddard Space Flight Center, led by space scientists Geronimo L. Villanueva and Michael J. Mumma, report using Earth-based telescopes to observe the ratio of water and its deuterium-containing counterpart, DHO, over the entire planet.

The researchers, who made measurements over three martian years, found that water molecules, especially those near Mars’s polar regions, are highly enriched in deuterium. This implies that over time, lighter, regular water (H₂O) has escaped into space, leaving the heavier DHO behind. According to the group’s models, the planet has lost 87% of its water over several billion years. This amount of water could have formed an ocean up to a mile deep, covering about 20% of the planet’s northern area.

“With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting the planet might have been habitable for longer,” Mumma says.