It’s hard to believe it now looking at Mars’ dusty, dessicated landscape that it once possessed a vast ocean. A recent NASA study of the Red Planet using the world’s most powerful infrared telescopes clearly indicate a planet that sustained a body of water larger than the Earth’s Arctic Ocean.

If spread evenly across the Martian globe, it would have covered the entire surface to a depth of about 450 feet (137 meters). More likely, the water pooled into the low-lying plains that cover much of Mars’ northern hemisphere. In some places, it would have been nearly a mile (1.6 km) deep. 

Three of the best infrared observatories in the world were used to study normal to heavy water abundances in Mars atmosphere, especially the polar caps, to create a global map of the planet’s water content and infer an ancient ocean. Credit: NASA/ GSFC

Now here’s the good part. Before taking flight molecule-by-molecule into space, waves lapped the desert shores for more than 1.5 billion years – longer than the time life needed to develop on Earth. By implication, life had enough time to get kickstarted on Mars, too.

A hydrogen atom is made up of one proton and one electron, but its heavy form, called deuterium, also contains a neutron. HDO or heavy water is rare compared to normal drinking water, but being heavier, more likely to stick around when the lighter form vaporizes into space. Credit: NASA/GFSC

Using the three most powerful infrared telescopes on Earth – the W. M. Keck Observatory in Hawaii, the ESO’s Very Large Telescope and NASA’s Infrared Telescope Facility – scientists at NASA’s Goddard Space Flight Center studied water molecules in the Martian atmosphere. The maps they created show the distribution and amount of two types of water – the normal H2O version we use in our coffee and HDO or heavy water, rare on Earth but not so much on Mars as it turns out.

Maps showing the distribution of H20 and HDO (heavy water) across the planet made with the trio of infrared telescopes. Credit: NASA/GSFC

In heavy water, one of the hydrogen atoms contains a neutron in addition to its lone proton, forming an isotope of hydrogen called deuterium. Because deuterium is more massive than regular hydrogen, heavy water really is heavier than normal water just as its name implies. The new “water maps” showed how the ratio of normal to heavy water varied across the planet according to location and season. Remarkably, the new data show the polar caps, where much of Mars’ current-day water is concentrated, are highly enriched in deuterium.

It’s thought that the decay of Mars’ once-global magnetic field, the solar wind stripped away much of the planet’s early, thicker atmosphere, allowing solar UV light to break water molecules apart. Lighter hydrogen exited into space, concentrating the heavier form. Some of the hydrogen may also departed due to the planet’s weak gravity. Credit: NASA/GSFC

On Earth, the ratio of deuterium to normal hydrogen in water is 1 to 3,200, but at the Mars polar caps it’s 1 to 400.  Normal, lighter hydrogen is slowly lost to space once a small planet has lost its protective atmosphere envelope, concentrating the heavier form of hydrogen. Once scientists knew the deuterium to normal hydrogen ratio, they could directly determine how much water Mars must have had when it was young. The answer is A LOT!

Goddard scientists estimate that only 13% of Mars’ original water reserves are still around today, concentrated in the icy polar caps. The rest took off for space. Credit: NASA/GSFC

Only 13% of the original water remains on the planet, locked up primarily in the polar regions, while 87% of the original ocean has been lost to space. The most likely place for the ocean would have been the northern plains, a vast, low-elevation region ideal for cupping huge quantities of water. Mars would have been a much more earth-like planet back then with a thicker atmosphere, providing the necessary pressure, and warmer climate to sustain the ocean below.

Mars at the present time has little to no liquid water on its cold, desert-like surface. Long ago, the Sun almost certainly saw its reflection from wave-rippled lakes and a northern ocean. Credit: NASA/GSFC

What’s most exciting about the findings is that Mars would have stayed wet much longer than originally thought. We know from measurements made by the Curiosity Rover that water flowed on the planet for 1.5 billion years after its formation. But the new study shows that the Mars sloshed with the stuff much longer. Given that the first evidence for life on Earth goes back to 3.5 billion years ago – just a billion years after the planet’s formation – Mars may have had time enough for the evolution of life.

So while we might bemoan the loss of so wonderful a thing as an ocean, we’re left with the tantalizing possibility that it was around long enough to give rise to that most precious of the universe’s creations – life.

To quote Charles Darwin: “… from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Illustration showing Mars evolving from a wet world to the present-day where liquid water can’t pond on its surface without vaporizing directly into the planet’s thin air. As Mars lost its atmosphere over billions of years, the remaining water, cooled and condensed to form the north and south polar caps. Credit: NASA/GSFC
Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.

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