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The Hot Baths of Mars

The views expressed are those of the author and are not necessarily those of Scientific American.


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Once upon a time on Mars... (Credit: USGS/R. Fournier)

To understand Mars we need to understand its on-again off-again tango with liquid water. It’s not just the search for past or present life on Mars that hinges on this, but the search for a complete chemical, geophysical, and climatological history of the red planet. Water is such a potent agent for topographical and mineralogical alteration that its presence leaves layer upon layer of complex clues – the challenge is to pick these apart.

When Curiosity recently discovered clear evidence for a dried up stream-bed in the alluvial fan of a crater this was one example of how Mars’ history is littered with episodes where liquid water gushed, seeped, and likely pooled on the planetary surface.

Now a remarkable new study has not only found evidence of liquid water on Mars and its chemical impurities, but also the actual temperature at which it existed. The clues come from one of the best resources we have for studying Mars without actually going there – martian meteorites. The ‘nakhlites’ are a class of igneous rock (frozen magma) that formed on Mars about 1.3 billion years ago, were blasted from the surface in a giant impact event about 11 million years ago, and have been falling onto the Earth during in the past 10,000 years (including in 1911.)

Based on the ages at which these rocks crystallized and the chronology of martian craters we can even place their origin somewhere on the volcanic plains of northern Mars, either Tharsis or Syrtis Major. Studying the detailed structure and chemical ‘veins’ in these meteorites provides a unique probe of the conditions in which they once existed on Mars. Publishing in the December issue of Earth and Planetary Sciences Letters, the authors Bridges and Schwenzer present an investigation of the mineralogical structures in one of the nakhlite rocks using electron microscopy.

A cradle of life? Part of Tharsis region on Mars (Mars Express/ESA)

What they find is clear evidence for a progression of minerals deposited in the rock veins that could only occur in the presence of hot liquid water. First is iron carbonate – which crystallizes out from carbon-dioxide rich water at about 150 Centigrade (super heated), followed by clay-like minerals that form as the water cools down to about 50 Centigrade. All of this stuff has been enriched by sodium and potassium salts – in a slightly alkaline mix. In other words, these rocks were bathed in the equivalent of a hot briny spring.

So what could have driven this sort of environment millions of years ago on Mars? The authors speculate that an earlier asteroid impact on Mars could have melted carbon-dioxide rich water ice and forced it under pressure into the surrounding terrain – like a great hand smacking into a wet sponge. This hot water would have flowed and percolated through the subsurface of the volcanic plains, gradually cooling down and depositing all the minerals we see.

Although the nakhlite rocks might have only been seeped in these hydrothermal waters for a few months there is evidence that the deeper rocks they once sat on could be part of a much longer lived wet and chemically rich environment. And this particular type of environment is a direct analog to hydrothermal systems here on Earth, with hot water and the kind of low-acidity, salt-rich chemistry that we know is very much habitable for all manner of microbial organisms.

All of which I think suggests once again that Mars really has, and used to have, a strong potential for life – but the fundamental nature of the Martian habitable zone is different from that of Earth. It appears to have been episodic, and reliant on mechanisms such as impact events in ways that may be unique to this dusty red world.

 

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. Bill_Crofut 6:10 pm 11/16/2012

    Dr. Scharf,

    Re: “The ‘nakhlites’ are a class of igneous rock (frozen magma) that formed on Mars about 1.3 billion years ago, were blasted from the surface in a giant impact event about 11 million years ago, and have been falling onto the Earth during in the past 10,000 years (including in 1911.)”

    It would be interesting to know what experiment has been conducted to demonstrate that any impact event could eject a martian rock into space and place it on an Earth-bound trajectory.

    Link to this
  2. 2. Caleb A. Scharf in reply to Caleb A. Scharf 7:03 pm 11/16/2012

    While no physical experiment has been carried out (a little tricky to do that), there is a wealth of mathematical modeling work that’s been done over the past 20-30 years to examine interplanetary transfer of impact ejecta. Turns out that it’s not that hard (given a decent asteroid impact), and that material is conveyed all across the solar system on a variety of timescales, from years to millions of years. Eject can go from Earth to Mars, Mars to Earth, and further afield – even between moons of the giant planets and the inner terrestrial worlds. A good paper is this: http://adsabs.harvard.edu/abs/1996Sci…271.1387G by Gladman et al. In addition, the identification of certain meteorites as being martian in origin is with high confidence, by measuring composition and isotopic ratios that pinpoint their origin.

    Link to this
  3. 3. Bill_Crofut 9:43 am 11/17/2012

    Dr. Scharf,

    Thank you for responding to my inquiry.

    Following the hyperlink you provided results in the following:

    “Preview or purchase options are not available”

    The Abstract, which is available, is not informative.

    A brief online search for the title, “The Exchange of Impact Ejecta Between Terrestrial Planets,” produced only one available paper: TOWARDS A SELF-CONSISTENT MODEL OF LUNAR AND MARTIAN METEORITE DELIVERY, http://www.lpi.usra.edu/lpi/meteorites/glaxxvii.html, which seems to consist entirely of simulations.

    It doesn’t occur to me how computer simulations and mathematical models can replace the evidence of experiments and/or observations to verify the claims.

    Link to this
  4. 4. Caleb A. Scharf in reply to Caleb A. Scharf 12:25 pm 11/17/2012

    Well, the best evidence lies in the existence of rocks (meteorites) that have absolutely no relationship to any other terrestrial compositions but which are an excellent match to the types of mineral compositions seen on Mars and which contain trapped gas molecules with precisely the same ratios and isotopic composition as measured in the martian atmosphere (both in-situ by the Viking mission and by remote telescopic observation). The Mars atmospheric mix is unique and a powerful fingerprint. You can get the PDF of a key review at: meteorite.unm.edu/site_media/pdf/MarsMeteorites.pdf

    Meteorites of lunar origin have also been found, and can of course be compared directly to Apollo samples, so there is considerable evidence for transfer between bodies in the solar system.

    Link to this
  5. 5. Quinn the Eskimo 9:30 pm 11/17/2012

    In other words, they’re makin’ stuff up, again.

    Link to this
  6. 6. Torbjörn Larsson, OM 10:46 pm 11/17/2012

    Ah, more evidence for mildly alkaline and wet environments. IIRC the MERs found similar evidences.

    @ Bill_Crofut:

    The problem separates into two parts, impact ejection of material and likelihood for transfer.

    The first part is easy, if we only want to see feasability. Take the Earth as example. If you take the orbital radius and time, you see that Earth orbits relative to the Sun at ~ 30 km/s.

    But its escape velocity is ~ 10 km/s. Even a large impactor standing still relative to the planets would have to launch some material, say in a glancing hit.

    Now the asteroids are corotating with the inner planets (at a lower speed), but depending on why they migrate towards the inner planets they end up having comparable velocities. An asteroid will have an average ~ 20 km/s impact velocity. Comets, falling all the way from the Oort cloud, will have much more, some ~ 50 km/s impact velocity on average.

    Mars moves slightly slower in orbit, but have a lower escape velocity. (IIRC ~ 6 km/s vs ~ 11 km/s.)

    Now you can question the details of the physics of the impacts. But these impactors move with hypervelocity, that is faster than the speed of sound in rocks (~ 2-3 km/s in crystals). In which case sound waves won’t suffice to transfer energy out from the impact area and convert it to heat.

    Instead the impacts generates shock waves which some of the energy goes into. And there you have shock waves, you will easily launch ejecta. IIRC, they model ejection of masses of ~ 3-5 % of the impactor mass. Mostly rocks from the impacted area too, the impactor will vaporize and melt et cetera.

    As for transfer likelihoods, I assume they get out roughly the observed rate of transfer without any problem. You should be able to estimate the observed rate from estimates of incoming material (you know sizes and frequency from radar observations and what not) and the ratio of, say, martian meteorites to the others.

    So that small part of the phenomena is not a problem. There has to be a feasible mechanism if you find these interplanetary travelers for certain. And as it happens, there is such a mechanism and it is reasonably easy to make a back-of-the envelope sketch of the physics.

    Link to this
  7. 7. Torbjörn Larsson, OM 10:54 pm 11/17/2012

    “And there you have shock waves, you will easily launch ejecta.”

    Actually, the correct claim would be that you would have difficulty _not to_ launch ejecta.

    And as we see from the simulations, it must be a fairly efficient process. And really, where would fragments go, caught between a rock and a hard place?

    Link to this
  8. 8. Bill_Crofut 9:43 am 11/19/2012

    Dr. Scharf,

    Thank you for the url. It’s my plan to review the document.

    Link to this
  9. 9. Bill_Crofut 9:44 am 11/19/2012

    Torbjörn Larsson,

    You seem to have summed up your position well in comment 7: “simulations” and “must be.”

    Still, simulations and assertions are no substitute for physical evidence.

    Link to this
  10. 10. Bill_Crofut 8:18 am 11/20/2012

    Dr. Scharf,

    Re: The SNC meteorites are from Mars
    http://meteorite.unm.edu/site_media/pdf/MarsMeteorites.pdf

    The first two sentences in the abstract would seem to have set the stage:

    The first sentence, “The 14 SNC meteorites are all igneous rocks, either basalts or basaltic cumulates.” could just as well be describing rocks of Earth orgin.

    The second sentence, “They are inferred to be from Mars, based on direct comparison with Martian materials and on consistency with inferences about Mars,” contains two variations of infer.

    That does not seem to me to constitute verifiable evidence of Martian origin.

    The second paragraph in the Introduction contains the following statement:

    “…[A]s shown by debates at the SOCFI conference in Paris, France (February 1-5, 1999), there is still some uncertainty in the international scientic community about the link between SNC meteorites and Mars…”

    That admission does not seem to square with the definitive tone of the title: “The SNC meteorites are from Mars.”

    The first sentence in paragraph 3 of the Introduction reads:

    “We feel it is useful to explore and restate the evidence linking the SNC meteorites with Mars, because so much mission planning for Mars Sample Return ultimately rests
    on inferences from these meteorites.”

    A third inference does not seem to me to add to the credibility of the claim.

    A cursory scan of the remainder of the paper seems to be technically descriptive information.

    Is there any particular section of the paper you would recommend reviewing in detail to substantiate the claim in the title?

    Link to this
  11. 11. bucketofsquid 6:20 pm 11/20/2012

    @Bill_Crofut – You make very good points however, do you have a falsifiable alternate explanation of where these meteorites came from? It seems to me that you are cherry picking data to support a prior conclusion. The statements detailing structures and chemical make-up are pretty specific but you choose not to address them at all. Perhaps you should study the original blog post and the entire referenced article. stating that you didn’t bother to read the technical detail just shows you to not be a creditable source of legitimate review/criticism.

    Personally I think the only way to really prove it is to pinpoint the area as closely as possible and send a Mars expedition there to see if the rocks reasonably match.

    Link to this
  12. 12. rlynde 7:30 pm 11/20/2012

    @10. Bill_Crofut:
    “The first sentence, “The 14 SNC meteorites are all igneous rocks, either basalts or basaltic cumulates.” could just as well be describing rocks of Earth orgin.”
    Mr. Crofut, the detailed geochemistry of the SNC basalts or basaltic cumulates indicate that they could not just as well be describing rocks of Earth origin. This is true also of the basalts and basaltic cumulates brought back from the moon.

    Link to this
  13. 13. Bill_Crofut 9:54 am 11/21/2012

    bucketofsquid,

    Regarding a falsifiable alternative, the rocks were found on Earth because they are of Earth origin.

    You’re absolutely correct in recognizing my prior conclusion. That conclusion is based on my incredulous reaction to the proposition that an impact is going to dislodge a rock from the moon or Mars and position it on a trajectory that will eventually cause it to land on Earth. Where is the experimental evidence that any such event has ever occurred?

    Link to this
  14. 14. Bill_Crofut 9:55 am 11/21/2012

    rlynde,

    Do we have igneous and basaltic rocks on Earth?

    Link to this
  15. 15. caleb_scharf 2:30 pm 11/21/2012

    Even if you are skeptical of the martian origin of these rocks there is the fact that the original Nakhlite meteorite that impacted Earth in 1911 deposited chunks of material (in some cases making clear holes in the ground) that I think can have no origin other than extra-terrestrial. So then you need to present a really good hypothesis for why these extraterrestrial rocks should just happen to have such a perfect compositional, isotopic, and geo-physical match to the martian environment and no-where else in the solar system.

    I also, personally, don’t think that an ‘incredulous reaction’ to the idea that an asteroid impact can dislodge material to interplanetary, planet crossing, trajectories is a scientific response – especially when you’ve seen the wealth of quite straightforward physics arguments and calculations that tell us this is indeed totally plausible.

    It’s one thing to be a skeptic, it’s another to effectively disrespect and dismiss without any basis the hard work of innumerable scientists – especially when you are presumably sitting at a computer that is the direct result of all those ‘implausible’ ideas like quantum mechanics and relativity.

    Sorry, but I felt I had to say that.

    Link to this
  16. 16. Bill_Crofut 11:46 am 11/22/2012

    Dr. Scharf,

    You need not have apologized for expressing your point of view, especially since you’re dealing with an unlettered layman. It seems to me that’s the point of a comments venue.

    That having been admitted, my skepticism is based on what seems to me a lack of experimental evidence for a bolide impact that is allegedly capable of transporting a piece of rock from one solar system body to another. Aside from computer simulations and assertions, what is the evidence that such an alleged event has physically occurred? Please note my skepticism is in the form of a question.

    Link to this
  17. 17. rlynde 8:32 pm 11/23/2012

    @14. Bill_Crofut 9:55 am 11/21/2012
    “rlynde,
    Do we have igneous and basaltic rocks on Earth?”

    Mr. Crofut,
    Of course there are basaltic and other igneous rocks on Earth, and they have very specific detailed geochemical compositions. Likewise, there are basaltic and other igneous rocks on the moon, and they have very specific detailed geochemical compositions that are different than basaltic and other igneous rocks on the Earth. And finally, as I pointed out in my response above:
    “the detailed geochemistry of the SNC basalts or basaltic cumulates indicate that they could not just as well be describing rocks of Earth origin,” or of lunar origin either.

    Link to this
  18. 18. Bill_Crofut 9:14 am 11/24/2012

    rlynde,

    Re: “Of course there are basaltic and other igneous rocks on Earth…”

    Ok. That’s part of the point of my argument. Where is the evidence that the ‘nakhlites’ were blasted to Earth from the surface of Mars? The rocks in question were found on Earth. Where is the evidence that they were not always Earthen rocks?

    Link to this
  19. 19. caleb_scharf 3:52 pm 11/26/2012

    Bill_Crofut – apologies if I’m confused here, but if you agree that meteorites are real then you must agree that the ‘nakhlites’ are at least extraterrestrial in origin? After all, people more or less burnt their fingers collecting these after they fell, hardly a spontaneous property of indigenous Earth rocks.

    As for the qn of ejection from Mars or elsewhere. In all honesty, no we do not have direct observation of this occurring. But the very clear physical possibility (i.e. from the laws of nature and computation) is clear, it is not something highly contrived. As with so much science the evidence is in the accumulated clues, which I think taken together are pretty overwhelming. Does that mean it’s 100% proven? No, but such is the nature of science – it is a progression of questions and answers that can be assessed at each stage in as much quantitative detail as possible.

    Link to this
  20. 20. Bill_Crofut 9:56 am 11/27/2012

    Dr. Scharf,

    There’s no question in my mind that meteorites are real. However, in my experience no one has made the claim that they exist as a result of bolide impact on any solar system body. That’s the sum total of my hang-up. It’s my understanding that hypotheses will remain so until tested. What is the test of the bolide-impact hypothesis for the origin of the alleged lunar/martian rocks found on Earth? Has anyone even proposed a test?

    Link to this

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