Various robotic probes that have been sent to the Red Planet, such as the Mars Curiosity rover (1), have confirmed this hypothesis.
Mars Curiosity, for example, has found clay and other rocks that were formed by running water. The robotic rover has also determined that the landscape, now arid, used to have water flowing through it.
Over billions of years, Mars’ atmosphere was gradually lost into outer space because of that planet’s lower gravity. At the same time, Mars’ water was lost as water molecules also leached away into space. The rest of the water became frozen at the Red Planet’s poles. Some of the water may still be trapped beneath the Martian soil.
Still, scientists are curious about how much water Mars may have had in the distant past, billions of years ago.
Toward that end, NASA’s Goddard Spaceflight Center (2) employed three infrared telescopes, the European Southern Observatory’s Very Large Telescope in Chile, and the W.M. Keck Observatory and NASA Infrared Telescope Facility in Hawaii to study the various types of water molecules in the Martian atmosphere over a number of seasons.
Comparing Water Molecules
NASA compared two types of water molecules, the more familiar H20 and HDO, a form of heavy water in which one of the hydrogen atoms is replaced by deuterium. The ratio, mapped over six Earth years, was compared to the ratio of types of water trapped in a Martian meteorite that dated from 4.5 billion years ago.
The researchers found that water over the Martian northern hemisphere is far more highly enriched with heavy water than water on Earth. While normal water escaped into space, the heavy water remained.
Using these measurements, and noting that a region in the Martian northern hemisphere is depressed compared to the rest of the Martian landscape, NASA scientists deduced that Mars once had an ocean that covered 19 percent of the planet’s surface and with a depth greater than a mile. Roughly 87 percent of Mars’ water has escaped into space, with the remainder largely trapped in the polar ice caps.
A truism states that where water exists, life may also exist. According to NASA (3), the holy grail of Mars exploration is the search for evidence that life existed on Mara during its wet period, which ended 3.7 billion years ago. More importantly, scientists wonder if life still exists on the Red Planet, perhaps as microbes burrowed beneath the soil where warmth and perhaps some remnants of water persist.
Thus far, the results of decades of exploration by both NASA, the Indian Space Research Organization and the European Space Agency have proven to be inconclusive.
One possible clue was recently discovered in the form of traces of methane (4) in the Martian atmosphere. While methane could have a geologic origin, another possibility is that it is being produced by the suspected Martian microbes thought to exist beneath the Martian surface.
The Future of Mars
If Mars had a thick atmosphere, running water, and perhaps life, could it have these things again?
Some space visionaries imagine that future Mars settlers could terraform the Red Planet (5).
The temperature of Mars could be gradually raised using orbiting mirrors and by other means. Comets could be diverted to smash into Mars to add water and other volatiles to create a greenhouse effect. Plants and animals could be introduced that would create a Martian ecosystem.
Using technology imagined currently, the transformation of Mars would take several thousand years. But at the end of that time, the ocean once lost would return, with rivers, streams, and lakes. Mars, the red planet, would become a second blue planet and, thus, a second Earth for humans to live on.