Extensive water in Mars' interior

Jun 21, 2012
Mars, as seen by the Hubble Space Telescope. Image credit: NASA

Until now, Earth was the only planet known to have vast reservoirs of water in its interior. Scientists analyzed the water content of two Martian meteorites originating from inside the Red Planet. They found that the amount of water in places of the Martian mantle is vastly larger than previous estimates and is similar to that of Earth's. The results not only affect what we know about the geologic history of Mars, but also have implications for how water got to the Martian surface. The data raise the possibility that Mars could have sustained life.

The research was led by former Carnegie postdoctoral scientist Francis McCubbin, now at the University of New Mexico. The analysis was performed by Carnegie Institution investigator Erik Hauri and team and is published in the journal .

The scientists analyzed what are called shergottite meteorites. These are fairly young meteorites that originated by partial melting of the Martian mantle—the layer under the crust—and crystallized in the shallow subsurface and on the surface. They came to Earth when ejected from Mars approximately 2.5 million years ago. Meteorite geochemistry tells scientists a lot about the geological processes the planet underwent.

"We analyzed two meteorites that had very different processing histories," explained Hauri. "One had undergone considerable mixing with other elements during its formation, while the other had not. We analyzed the water content of the mineral apatite and found there was little difference between the two even though the chemistry of trace elements was markedly different. The results suggest that water was incorporated during the formation of Mars and that the planet was able to store water in its interior during the planet's differentiation."

Based on the mineral's , the scientists estimated that the Martian mantle source from which the rocks were derived contained between 70 and 300 parts per million (ppm) water. For comparison, the upper mantle on Earth contains approximately 50-300 ppm water. Hauri and team were able to determine these values with new techniques and new standards they developed that can quantify water in apatite using a technology called secondary ion mass spectrometry (SIMS).

"There has been substantial evidence for the presence of liquid water at the for some time," Hauri said. "So it's been puzzling why previous estimates for the planet's interior have been so dry. This new research makes sense and suggests that volcanoes may have been the primary vehicle for getting water to the surface."

McCubbin concluded, "Not only does this study explain how Mars got its water, it provides a mechanism for hydrogen storage in all the terrestrial planets at the time of their formation."

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User comments : 13

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Vendicar_Decarian
3 / 5 (8) Jun 21, 2012
This is excellent news for game show contestants who will soon be living on Mars.

Or not.
dogbert
4.5 / 5 (4) Jun 21, 2012
This is a lot of water for a planet with little or no water on the surface now.

The estimate is based on subsurface water during the formation of rocks over 2.5 million years ago. Can we extrapolate water content today based on that estimate?
Torbjorn_Larsson_OM
4 / 5 (4) Jun 21, 2012
Tremendous news!

The original parent magma contained 10 times as much water, or ~ 700 - 3000 ppm water, see the abstract.

*** This predicts the generic water evolution and content on terrestrials! ***

They are pretty dry compared to your average asteroid chondrite, that has ~ 15-20 % water by mass. Earth-Moon and Mars now initially had ~ 0.5 % water by mass which Earth mostly retains. 5 times less and we would likely not have plate tectonics (Earth is a runt, as terrestrials go, so plate tectonics is marginal), 5 times more and we would have no continents.

But with a generic fine dryness after the aggregation process, there should be extensive habitability as we know it in exoplanets placed in the habitable zone.

And as the press release has the scientists note, water volatile evolution after aggregation by volcanic activity should now suffice - here, on Mars and everywhere.

@ dogbert: Yes, see above and the abstract. (Paper paywalled.)
Torbjorn_Larsson_OM
4.2 / 5 (5) Jun 21, 2012
Note also how this small amount of water makes a large difference in geology.

- It makes rocks malleable as we see in Earth plate tectonics. So it promotes mantle convection and an active geology for a longer time.

- Water is the predominant factor making magmatic basalts convert to the eutectic granite. (An eutectic is the lowest melt point mixture.) This is the light rock that makes up our continental plate floats. It should have similar importance for Mars geology dynamism even without bona fide plates, separating and moving rocks.
casualjoe
5 / 5 (1) Jun 22, 2012
They came to Earth when ejected from Mars approximately 2.5 million years ago.

You know, I never quite got how that bit worked.
kevinrtrs
1.1 / 5 (12) Jun 22, 2012
Firstly, how do they know that these pieces of rock were ejected from Mars about 2.5 million years ago? What records did they consult that showed that these particular rocks left the surface of Mars that long ago?
Or more to the point - what assumptions were made to interpret their measurements on the rock contents?

Secondly, if these rocks were ejected so long ago, when did they arrive here on earth? If the rocks had been here for over a million years would it be possible that they somehow got contaminated?

Perhaps one should really ask - if the rocks are meteorites that only recently entered the earth's atmosphere and plunged down to earth, where were they for the rest of the time after ejection 2.5 million years ago?

The inference of water obtained from the rocks doesn't guarantee that Mars has subterranean water. Until such time as a probe or mission actually confirms the report, this is a tentative prediction.

Then of course, water on Mars does not guarantee life either.
verkle
2 / 5 (5) Jun 22, 2012
Casualjoe, there is a great planet simulator at this link:

http://lasp.color...mulator/

By defining a planet "X", we can somewhat simulate a path that such a meteor would have to take. It would have to be ejected at some relative speed to Mars to put it in an eccentric orbit that would cross the vicinity of Earth. My initial calculation shows that in the very best case (assuming the 3D angle is exactly right) it would have be ejected at a relative velocity of about 2km/sec to reach the orbit of the earth. This does not take into account the escape velocity from Mars, so actual velocity would be even higher than that.

Whether such a scenario is really realistic or not is another question, let to be answered by other experts.

Osiris1
1 / 5 (6) Jun 22, 2012
Let us see...all the eggheads pontificated on a dry Mars, and professionally ignored all evidence to the contrary. More than that, every new piece of evidence of a watery Mars was actively criticised, and many of these 'worthies' went waaaaay out of their way to conjure up increasingly unbelievable scenarios of 'wind deposition', other exogeological processae, and other fairy tails. One wonders why! Was it borne of religious insecurity? Silly when the idea of other places are clearly stated in the Bible in many verses all over the Old and New Testaments.....and even in the Qu'ran. Or was it job fears pontificating as scholasticism. In any case the truth will out...and has. And so will Martian life's truth be exposed, perhaps spectacularly if a Chinese probe suddenly finds unequivocal evidence and gleefully presents it to a world full of quasi-scientific charlatans. And finally, like Copernicus, those who have suffered this bullying will be vindicated. Publicly!
roboferret
5 / 5 (1) Jun 22, 2012
those who have suffered this bullying will be vindicated. Publicly!

Don't hold your breath.
Torbjorn_Larsson_OM
1 / 5 (1) Jun 22, 2012
"how do they know that these pieces of rock were ejected from Mars".

The paper will contain references, but most people know this or have the energy to find the Wikipedia article. Of course, creationists are far from that knowable. ("Encyclopedias?")
casualjoe
5 / 5 (1) Jun 23, 2012
It's ok I get it now, Martian rocks explain the SNC group of meteorites discovered all over the world. Our solar system has had a pretty active past! Also, that massive volcano on Mars must have once been much more active.
Torbjorn_Larsson_OM
1 / 5 (1) Jun 24, 2012
Casualjoe, verkle has the gist. This is how the rest works, at least according to my astrobiology course book:

A planet travels @ ~ 20-40 km/s in its orbit relative to the Sun, and so does impactors relative to the planetary orbit (comets even faster, arriving by descending a huge gravity well). Thus then they it rocks they constitute hypervelocity impactors, meaning their impact speed is much faster than the speed of sound in rocks @ ~ 2-3 km/s.

The result is shock waves that launches a huge ejecta plume from an impact site that has a radius ~ 20 times the impactor radius. You get that scaling up of the dug hole in the ground from considering impact energies. It is also confirmed in some cases by finding the impactor remains and make a size estimate.

~ 5 % of ejecta from Earth is able to reach above escape velocity @ ~ 11 km/s in impact models. On Mars, even more as it has lower escape velocity. And nowadays a less dense atmosphere, and IIRC when the shergottites were launched.
GSwift7
not rated yet Jun 26, 2012
The estimate is based on subsurface water during the formation of rocks over 2.5 million years ago. Can we extrapolate water content today based on that estimate?


and

Let us see...all the eggheads pontificated on a dry Mars, and professionally ignored all evidence to the contrary. More than that, every new piece of evidence of a watery Mars was actively criticised


Just to clarify, they aren't talking about reservoirs of liquid water underground. The water in this case is individual water molecules, chemically bound to rocks and minerals in the interior layers of the planet.