Where Did All of Mars' Water Go? Apparently Not Very Far

A new theory proposed by scientists at Oxford says that most of the water is still there, in the planet's crust

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Modern Mars, dry and barren (left), compared with the same scene over 3.5 billion years ago (right), covered in water.
Modern Mars, dry and barren (left), compared with the same scene over 3.5 billion years ago (right), covered in water.
Ruth Schuster
Ruth Schuster
Ruth Schuster
Ruth Schuster

Around three billion years ago, Mars wasn’t a frozen red planet but a warm one where water flowed. Some even suspect the whole or much of the planet was at some point covered by ocean that may have been as much as 3 kilometers deep.

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There is no consensus about how much water Mars once had, but it did have a lot, and the question is, what happened to all that water? The assumption had been that most was lost to space or sank below the surface and froze. Now scientists at Oxford propose a new theory: It’s locked up in the rocks.

Whatever Mars’ atmosphere and temperature was as this happened, the loss of available water in and of itself would have made the planet uninhabitable, explains lead author Prof. Jon Wade.

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Earth has kept surface water since it cooled around 4.4 billion years ago, based on evidence from minerals called zircons, Wade explains. But Mars appears to have lost its water pretty fast, geologically speaking – within about 1.5 billion years of the planet’s accretion.

An image from NASA shows dark, narrow, 100-meter-long streaks called recurring slope lineae flowing downhill on Mars, inferred to have been formed by contemporary flowing water, September 27, 2015.Credit: AFP/NASA/JPL/UNIVERSITY OF ARIZONA

Some think the water was whisked away into outer space by solar winds when Martian magnetic field collapsed.

Mars is about 50 percent smaller than Earth, says Wade, so following the planets’ violent formation, it would have cooled faster, and so would its metal core. The spinning core is what gives a planet an active magnetic field, and as Mars’ metallic core cooled, the convection within it slowed and finally ceased – and there went the magnetic field.

Other scientists think the Martian water is squatting below the surface, as subsurface ice. (The loss of the magnetic field would have thinned the atmosphere, which would be less capable of holding onto heat.)

Now the Oxford team suggests that based on Mars’ chemistry, the water got taken up by the rocks. It has become one with the mantle, where it still remains.

Watery world

In 2015, NASA delighted Earthlings with the news that there is probably water on Mars right now.

While NASA couldn’t actually prove that, the space agency said the Mars Reconnaissance Orbiter had found signs of recurring liquid seepage along the sloping walls of craters. It also claimed that the seepage looked seasonal, indicating flows during warmer weather in spring and summer. Finally, certain salts were detected in the postulated flow paths that indicated the existence of brine. But if there is water, it isn’t frothing at our telescopes – there apparently isn’t much of it.

The Oxford team thought the answer to the riddle of the missing water might lie in Martian mineralogy. Using models usually employed to analyze the composition of rocks on Earth, they concluded that the Martian basalt can hold 25 percent more water than Earth’s basalt. The Martian basalt drew the water into itself, into the interior, they suggest.

“The chemistry of Martian rocks means they are more likely to react with the surface water, forming dense hydrous minerals,” Wade says. “In doing so, they will act to ‘lock up’ this surface water within the minerals and, over time, dry out the surface of the planet” – thus making the planet, if it ever was inhabitable, hostile to life.

It bears adding that the ability of the Martian rocks to lap up water doesn’t necessarily mean there’s none left. “We are suggesting that if there were lots of liquid water 4 billion years ago, as seems likely, some may still be present as ice, and some lost to space (which more recent data says is debatable),” he explains. But most water could have just been consumed by rock-water interaction and the formation of hydrous minerals.

Life on Mars

So, could there have been life on Mars?

The latest on life right here on Earth is that it began at least 3.5 billion years ago, probably earlier. Just this week, rocks found in Australia from that time have been all but categorically proven to contain not one but several forms of primitive bacteria-type life forms.

Of course, we still don’t know how the primordial soup or frisky dust bowls became “alive” and developed an agenda (Eat, procreate, kill everyone else), so we cannot even reasonably postulate whether this happened on Mars, or anywhere else.

Theoretically, Mars may have had conditions conducive to life. Surface features indicate that before the water vanished, Mars had flowing rivers, and hence temperatures above freezing at least for some periods of time.

That in turn implies that Mars also had a thicker atmosphere, which got stripped away by the solar winds as the magnetic field ebbed.

We on Earth are spared the eradication of our atmosphere by our magnetic field, which deflects the charged solar radiation particles that could “knock off” bits of the atmosphere, explains Wade.

In fact, Mars does still have a remnant magnetic field, Wade says. It’s not an active one generated by the core, but a small, residual one that comes from the iron-bearing minerals in the rocks, and oddly enough, it is only detectable on Mars’ southern half. We don’t know why.

The Oxford team thinks Mars would have lost its water even if it kept its magnetic field. Assuming these rock-water reactions were efficient, the crust could have absorbed even the 3-kilometer deep ocean that some think covered much or all of Mars. “In essence, Mars was doomed by its chemistry,” Wade concludes.

All that said, extremophilic germs here on earth, thriving in volcanic vents and ice, have shown one doesn’t need fripperies like oxygen or comfortable temperatures to exist. Could there, after all, still be life on Mars?

While noting that it isn’t his field, Wade also won’t rule it out. “But I can say it’s had a pretty miserable existence for the last few 3 or so billion of years!” he wrote to Haaretz. “I would suspect if life is there, it’s hanging on; and probably in places where it isn’t easy to find – deep underground.”

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