Mars Once Had an Ocean and Perhaps Life
A primitive ocean on Mars held more water than Earth's Arctic Ocean, but the Red Planet has lost 87 percent of that water to space. Image by NASA's Goddard Space Flight Center.
A primitive ocean on Mars held more water than Earth’s Arctic Ocean, according to a NASA-sponsored study that IfA astronomer Alan Tokunaga and graduate student Alain Khayat participated in. About 4.3 billion years ago, Mars would have had enough water to cover its entire surface in a liquid layer about 450 feet (137 m) deep. More likely, the water would have formed an ocean occupying almost half of Mars’ northern hemisphere, in some regions reaching depths greater than a mile (1.6 km). The wetter conditions mean that life was more likely to have existed on Mars than previously thought.
This new estimate is based on detailed observations made at the European Southern Observatory’s Very Large Telescope in Chile, and the W.M. Keck Observatory and NASA Infrared Telescope Facility in Hawai‘i. Tokunaga and Khayat gathered data with the two Hawai‘i telescopes.
The scientists used the ground-based observatories to measure water signatures in the Red Planet’s atmosphere. They distinguished the chemical signatures of two slightly different forms of water in Mars’ atmosphere. One is the familiar H2O. The other is HDO, a naturally occurring variation in which one hydrogen atom is replaced by a heavier atom called deuterium. By comparing the ratio of HDO to H2O in water on Mars today with the ratio in water trapped in a Mars meteorite dating from about 4.5 billion years ago, scientists measured the subsequent atmospheric changes and determined how much water has escaped into space.
The team mapped H2O and HDO levels several times over nearly six years, which is equal to approximately three Martian years. The resulting data produced global snapshots of each compound, as well as their ratio. These first-of-their-kind maps reveal regional variations called microclimates and seasonal changes, even though modern Mars is essentially a desert.
From the measurements of atmospheric water in the near-polar region, the researchers determined the enrichment, or relative amounts of the two types of water, in the planet’s permanent ice caps. The enrichment of the ice caps told them how much water Mars must have lost—a volume 6.5 times larger than the volume in the polar caps now. That means the volume of Mars’ early ocean must have been at least 5 million cubic miles (20 million cubic kilometers).
Based on the surface of Mars today, a likely location for this water would have been the Northern Plains, considered a good candidate because of the low-lying ground. An ancient ocean there would have covered 19 percent of the planet’s surface. By comparison, the Atlantic Ocean occupies 17 percent of Earth’s surface.