Mars Loses an Ocean But Gains the Potential for Life
by Bob King
on March 6, 2015

NASA
scientists have determined that a primitive ocean on Mars held more
water than Earth’s Arctic Ocean and that the Red Planet has lost 87
percent of that water to space. Water would have covered 20% of the
globe about 3 billion years ago. Credit: NASA/GSFC
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
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