Water on Mars: what does it mean?

September 29, 2015 • 8:45 am

Lots of folks have gone gaga about the discovery of salty water on the surface of Mars, and the excitement centers on one thing: the possibility that there could be life there. Well, we can’t rule out life yet, but the four Mars Rovers haven’t found any. What they have found are organic chemicals on the planet and sedimentary rocks with features resembling those formed by microbes on Earth, like stromatolites, stony structures built by cyanobacteria and—with some dated about 3.5-3.8 billion years old—the oldest definitive evidence of life on Earth. But what we see on Mars are only sort-of-similar rock structures; so far there has been nothing remotely resembling strong evidence of life (either past or present) on the Red Planet.

In a really nice post at the Planetary Society website, senior editor and “planetary evangelist” Emily Lackdawalla assesses the new evidence of briny water on Mars, and how it relates to the Big Question.

First, some photographic evidence for liquid water, with the caption:

Recurring slope lineae are narrow (0.5-5 m wide), relatively dark-toned features that form on steep (25-40˚), southern-hemisphere slopes, and that appear in early spring, grow longer in the downslope direction during spring and summer, and fade during autumn and winter.

The “linae” are the dark streaks that look like broomstraws; you can see them better in the black and white photos below.

Photo: NASA / JPL / UA / Emily Lakdawalla

Here are some of the seasonal changes that suggest moving water, as the “linea” (putative water channels) get longer over a season as they “flow” downhill toward the left (length of lines increases by the length of the white overlays). As noted below, these are probably growing channels of damp soil caused by moving water, rather than water rivulets themselves:

Photo: NASA / JPL / UA / Joe Levy

Here’s some of Lackdawalla’s summary, taken directly from her text (my emphasis):

  • Past work on slope lineae, with the HiRISE camera on Mars Reconnaissance Orbiter, showed that they form in warm seasons when temperatures reach 250-300 kelvin [JAC: on Earth pure ice melts above 273 kelvin, or 0°C], which strongly suggested that a volatile species like water was responsible.
  • The newly published work involves data from the CRISM spectrometer on Mars Reconnaissance Orbiter, and shows spectral evidence for hydrated salts (minerals containing molecular water in their structures) during the times when the slope lineae recur.
  • The best mineral matches to the spectral data are magnesium perchlorate, magnesium chlorate, and sodium perchlorate.
  • The presence of perchlorate salts could lower the melting temperature of water at Martian conditions by 40 kelvins, making it much easier for water to melt.
  • This work is considered very strong evidence that at widespread locations on present-day Mars, conditions sometimes arise for brief flows of briny liquid water — probably not rivulets, just spreading wetness in the soil.
  • The widely varying locations and geologic settings where slope lineae have been observed to form and recur make it difficult to identify a single mechanism for replenishing liquid water to drive the recurrent activity.
  • The science team including Ojha and Alfred McEwen favor deliquescence as the source: perchlorate salts adsorb water vapor from the atmosphere until enough water is available to form a liquid and dissolve the salts.

That’s all pretty clear, but what does it mean for the possibility of life? Lackdawalla doesn’t see these seasonal rivulets as propitious, but perhaps there’s life elsewhere on Mars:

Personally, I don’t think extant life on Mars is any more likely because of today’s announcement than it was before. An incredibly salty, corrosive, transient water environment is not a very good place to look for life. I think a much more habitable environment is available in the thin films of water that Phoenix observed in the soil at its near-polar landing site. A less-accessible, but also less-radiation-fried and more-continuously-habitable place would be deep underground, where Mars’ internal heat could keep groundwater liquid for very long periods of time.

Lackdawalla points out one concern that I hadn’t absorbed, also discussed by Lee Billings in a post at Scientific American: how can we find out whether there’s life on Mars if there’s a chance that, by visiting the planet, we ourselves could infect it? As Billings notes, spacecraft are scrupulously sterilized before launch, but that doesn’t solve the problem:

Microbes that stubbornly refuse to die nonetheless turn up with regularity in NASA’s supposedly sterile clean rooms for preparing interplanetary spacecraft. Apollo astronauts even found bacteria on the moon that had survived an almost total vacuum inside the robotic Surveyor 3 lander that had touched down more than two and a half years earlier. If terrestrial microbes could live in places like that, why not in some of the more habitable parts of Mars?

The issue becomes worse if humans, who are of course ridden with microbes, are sent to the planet, something that Lackdawalla, but not I, see as inevitable.

I’m not sure how serious this problem is, for, after all, all life on Earth shares certain features implying descent from a common ancestor. That includes the similarity of the genetic code, the use of L-amino acids, and the similarity of gene sequences among diverse species. Presumably if we found Earth-derived microbes on Mars, their DNA—and again, Mars-evolved life probably wouldn’t even contain DNA as we know it—would tell us. I suppose a greater problem is if Earth-derived life were to extirpate or outcompete Martian life, rendering us unable to detect the latter, but that seems unlikely as well. Martian life would probably be competitively superior to that from Earth, though we don’t know for sure (think of all the island species on our planet wiped out by colonizers!).

To cover my tuchus, let me add that it’s not impossible that life on Earth could have descended from life that evolved on Mars, or vice versa. In that case we’d see fundamental similarities among the genomes of species upon each planet, but big disparities between the heredity material of organisms from the two planets, reflecting their independent evolution since the colonization event.

Finally, Google has honored the finding in today’s Google Doodle:


h/t: Matthew Cobb

85 thoughts on “Water on Mars: what does it mean?

  1. I can’t resist a little H.G. Wells:

    …as men busied themselves about their various concerns they were scrutinised and studied, perhaps almost as narrowly as a man with a microscope might scrutinise the transient creatures that swarm and multiply in a drop of water. With infinite complacency men went to and fro over this globe about their little affairs, serene in their assurance of their empire over matter. It is possible that the infusoria under the microscope do the same. No one gave a thought to the older worlds of space as sources of human danger, or thought of them only to dismiss the idea of life upon them as impossible or improbable. It is curious to recall some of the mental habits of those departed days. At most terrestrial men fancied there might be other men upon Mars, perhaps inferior to themselves and ready to welcome a missionary enterprise. Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us. And early in the twentieth century came the great disillusionment.

    1. As we see today, lots of movies and television shows have plots around our current fears about terrorism (now likely from the mid-east). Not too long ago plots were wrapped around the cold war.
      I wonder what bogeymen was scaring people back in H.G. Wells’ time to inspire his stories?

      1. Like his contemporaries Bertrand Russell, G.B. Shaw, Oscar Wilde, and others among the Anglo and Irish intelligentsia, Wells was a socialist. He wrote his famous science-fiction works — The War of the Worlds, The Invisible Man, The Island of Doctor Moreau, The Time Machine — during the last half decade of the 19th Century (the so-called fin de siècle). This was the heart of the Belle Époque, or “Gilded Age” as it was called in America, a period marked by the rise of the robber barons and the business and banking trusts. It was also the zenith of the British Empire.

        My guess is that Wells’s works of speculative fiction from this period were informed by the excesses of the times — the way that the science-fiction of the 1950s was informed by the Cold War and the Red Scare.

        1. Interesting that in the US that was also “The Golden Age of Freethought,” though it was coming to a close. What a time.

  2. If they find a molecule of mol. wt. 100-500 I’d be shocked, let alone a molecule capable of making copies, and errors in those copies, of itself.

  3. I wonder to what extent are these channels are caused by liquid CO2. But the point that they advance during seasonal temperatures in the range of melting water does help one believe that water is involved, if not the sole cause of the channels.

    1. CO2 wouldn’t predict the presence of hydrated salts in the lineae but not elsewhere on the slopes.

      This was another tour de force of science.

      HiRISE has a resolution of .25 m at best, these lineae 1-2 m wide, the spectrometer CHRISM has ~ 20 m resolution.

      So they did what astronomers always do, science the shit out of their instruments. They characterized CHRISM until they found 6 [!] pixels that were superior, then integrated them over many passes above the widest lineae.

  4. how can we find out whether there’s life on Mars if there’s a chance that we ourselves could, by visiting the planet, infect it?

    I think we’d have to evaluate what we found. If it’s DNA-based or RNA-based at all, I’d say that the chances are we brought it. If its some simple replicator that doesn’t use either, then chances are very good that we didn’t.

    Of course we may find something “in the middle” – i.e, that uses some replication mechanism very similar to DNA and RNA. For those we’d have the question of whether it arose via convergent evolution or is some earth organism that underwent rapid, strong evolution over the last 50 years.* In this case, I’d look at how it breathes/what it eats and what its genetics say about how it evolved such capabilities. If the organism is well adapted to breath Martian air or subsist of Martian minerals – and we see no evidence in its DNA-like structure that it rapidly evolved the capability over the last few generations, then provisionally, I’d say it’s native. OTOH if it looks like it went through a recent, rapid period of adaptation or a genetic bottleneck, then I’d say it’s likely a hitchhiker from Earth. For example, does it have inactive genes that resemble genes used by earth bacteria? Then probably not Martian.

    *I’m assuming we’re worried about contamination from human and robot missions. Given that we occasionally find Martian rocks on Earth, I guess its possible for the reverse to happen and for some rocks ejected from Earth via natural processes, over the last few billion years, to make their way to Mars. I have no idea how you’d rule out that origin for some discovered organism, unless its genetics give clear indication that it’s related to some Earth organism.

    1. Given that we occasionally find Martian rocks on Earth, I guess its possible for the reverse to happen and for some rocks ejected from Earth via natural processes, over the last few billion years, to make their way to Mars.

      It’s a lot harder that way, since Mars is further out of the Sun’s gravitational well than Earth.

      Thus Mars –> Earth is “downhill” gravitationally, and it’s easy enough to think of trajectories that would take a Mars rock, blasted out of a volcano, to Earth. But Earth –> Mars is “uphill” and it’s much less likely that way round.

      1. But early in our histories there was a lot more bombardment, including some big ones. The theorized violent formation of our moon would have dropped a fair amount of earthly stuff on mars.

      2. The biological contamination sphere of Earth reach out to the moons of Saturn, where a target of Enceladus’s size would average one ejected crust piece over 4.5 billion years.

        [Reversely I think Earth is hit by ~ 200 kg/year martian meteorites.]

      3. I agree it’s unlikely for a rock to be blasted all the way from Earth to Mars in one go. But that’s not the only option; it can climb the solar gravity well the same way our spacecraft do: by multiple planetary flybys.

        A loose cloud of ejecta in Earth-crossing orbit must eventually experience another close encounter with Earth, at which point the individual ejecta orbits will be randomly perturbed; some will shrink, some will enlarge. But enlarging is not intrinsically less likely than shrinking; it’s more or less a 50-50 proposition, depending on whether the rock crosses Earth’s orbit ahead of or behind Earth.

        These new orbits are still Earth-crossing orbits. So we can expect the individual rocks to encounter Earth yet again at some point. And again, some orbits will shrink, and some will enlarge; and they’ll all still be Earth-crossing. With each encounter, the fraction of ejecta in large orbits shrinks, but the envelope of resulting orbits expands. Eventually, inevitably, it expands enough to include Mars-crossing orbits.

    2. The properties of RNA is likely such that it is a unique bottleneck for life. [See e.g. England’s thermodynamic calculations, RNA is the only know compound that can fulfill both roles as hereditary material and powerful enough enzyme to complete cellular self sustenance.] Further, the quaternary base pair language is pretty constrained to the ones we use.

      DNA isn’t unique I think. In the same manner I expect that other RNA life would evolve completely different machinery to produce proteins, et cetera.

  5. Like Lackdawalla said, the announcement only marginally distills any new merit to a claim of life on Mars.

    Water functionally changes the geology. Why doesn’t life? It does on earth. And life does change terrestrial (Marrestrial?) scale, is it only underground?

    1. Life does usually change geology. The problem is, we might be looking at some organism-changed geology and not know it, because we don’t know what it changed from.

      For surface minerals I don’t think this is a serious problem (we directly observe no surface life on Mars). But past life and underground life can’t be ruled out just on the basis of “all the minerals we see have at least one abiotic formation pathway.”

        1. Most of it, but not all.

          My point to Kevin is that we wouldn’t want to rule out life just based on observed geology, because many minerals can have multiple formation pathways. But you bring up sort of the reverse situation; we wouldn’t want to infer life based purely on observed geology either…for the same reason. 🙂

        2. I used to worry about that too. But now we have the methane detections, so maybe we are already seeing the biosphere.

          More pertinent, I just studied the first (I think) outer moon workshop 2013. Several people made the good point that without light – without oxygenating photosynthesis – the energy turnover decreases a factor 10. Moreover the geothermal heat flow of the moons (and Mars) are usually 1-3 oom less than on Earth.

          The upshot is that life would be marginal – if it exists at all after the moons/Mars started to cool – and (this is me) it is nontrivial whether or not we can expect them to dominate element cycles as on Earth.

          1. Strike “exists at all”. I forgot that those people assumed non-patchy conditions for the ice moons. Not true on Mars in any case, lot of variety there.

          2. “Marginal” on a planetary scale could still represent huge ecosystems. There’s 10E8-10E9 bacteria per teaspoon of dirt on Earth. Reduce that by 3 oom and you’ve still got a huge ecosystem. Eliminate all life within 2m of the surface and you’ve still got a huge ecosystem. Locate it a mile under ice on a moon of Saturn and it’s still a huge ecosystem.

            Do I think such huge ecosystems exist? No, I think that’s very unlikely. However, I would not say they are impossible based on energetics; reduce the solar and geothermal outputs by 3, heck 6 orders of magnitude, there is still plenty of energy available for life.

  6. What is the definitive scientific definition for organic? Carbon, and hydrogen containing compounds derived from living things?

    1. Historically the term organic in the context of chemistry was meant to denote “derived from living things” because living things were the only known source of organic compounds at the time.

      But that is no longer the case. As more and more organic compounds were discovered, as the composition and structure of organic compounds was discovered, it became more and more evident that organic compounds are created by non living processes.

      Famously, organic compounds have been detected many times within intergalactic molecular clouds.

      These days organic means merely compounds that contain carbon. The reason for the special treatment of carbon containing compounds is because carbon is so amenable to creating bonds with so many other atoms, and itself of course, that myriads of compounds from relatively simple to hugely complex, and with a huge variety of properties, are possible thus enabling all kinds of cool and useful chemistry. Like life.

  7. The need to get humans to this or any other place in space seems like old thinking in some way. We can probably investigate as well with more advanced robots and other devices and the cost will be far less and more reasonable. Our technology still puts human travel in space at the greatest cost and certainly the greatest risk. The U.S. alone has lost 17 humans in the past and that was right here in our own backyard. So it’s not a matter of, is it worth it but more a question – is it necessary?

    In modern military aircraft we are already beginning to leave the age of pilot in the cockpit behind. Before long there will be no pilots in the planes because the planes of the future will perform better and cheaper without them. Putting the humans in space will probably be left to Hollywood.

    1. The cost argument could be flawed. Human exploration is faster and so cheaper ROI.

      “There is a widely held view in the astronomical community that unmanned robotic
      space vehicles are, and will always be, more efficient explorers of planetary surfaces
      than astronauts (e.g. Coates, 2001; Clements 2009; Rees 2011).

      Partly this is due to a
      common assumption that robotic exploration is cheaper than human exploration
      (although, as we shall see, this isn’t necessarily true if like is compared with like), and partly from the expectation that continued developments in technology will
      relentlessly increase the capability, and reduce the size and cost, of robotic missions
      to the point that human exploration will not be able to compete.

      I will argue below
      that the experience of human exploration during the Apollo missions, more recent
      field analogue studies, and trends in robotic space exploration actually all point to
      exactly the opposite conclusion.”

      [ http://arxiv.org/ftp/arxiv/papers/1203/1203.6250.pdf ]

      1. The main argument for human exploration is our ability to both work quickly and to innovate in unexpected situations. Everything that the Opportunity rover has accomplished in ten years on the surface could have been accomplished by a team of people in a few weeks.

        The counter argument, of course, is the cost, the risk, and the difficulty of crewed missions.

        Personally, I do not think we are ready for a crewed mission, as much as I would like to see one happen. The fundamental limiting factor here is the need to protect the crew from radiation. We do not know how to do that without making the spacecraft so massive that it would be useless. Since a mission to Mars could easily last several years, I think it would be foolhardy at this point in time to try. We might bring back corpses or people who are about to become corpses.

        Also, the folks who are currently planning a one way mission need to rethink it. Anyone who goes probably won’t live more than a few years unprotected.

        Also, perchlorates seem to be ubiquitous on Mars. They are highly toxic. We need to figure out to protect the crews from those substances.

        At the risk of repeating myself, we are not ready.

        1. Before any of those significant concerns, we’d first have to figure out what the astronauts would breathe — and then what they’d drink and eat. And they won’t be getting any (convenient) resupply missions, either, so spare parts are going to be critical.

          Also, for all talk about colonization…how is one supposed to make plastics, rubber, integrated circuits, all the rest with the raw materials on Mars? You can bootstrap that sort of thing with initial supplies from Earth…but a colony is going to have to be self-sustaining…and a Martian colony is going to have to have its own complete highly-industrialized economy just to be able to maintain the living quarters and agricultural operations. Oh, did I mention agriculture? Crops need air, too….


          1. Right. I think a colony would need Earth’s support for a very long time. Enough time to terraform Mars into a more survivable planet.

            1. …and, again, there’s nothing we could ever do to Earth to make it as inhospitable as Mars is, which should give some idea as to what it would take to make Mars hospitable. It’s much easer to destroy than to create….


              1. With that in mind, it’s easier for me to imaging Mars remaining an interesting subject of scientific research rather than destination for colonization. Once Earth’s population settles back down to appropriate levels, this will be the best of all possible worlds.

              2. Yes.

                We’re just simply never going to colonize Mars. It’d be cheaper and easier to colonize the Moon and the asteroids…and, once you’ve colonized the asteroids, there’s no further attraction to colonizing any other planets. The next significant use for planets after that, aside from science and tourism, is as raw materials…and that’s only after we’ve used up all the raw materials in the asteroids and planetary ring systems and the like. At that point, we’re talking about Dyson Spheres and Ringworlds, and so far beyond technology as we can imagine it…but there’s no middle ground that includes planetary colonization.


              3. Great minds, as they say…
                You took the thoughts right out of my brain – Dyson chicken balls and the trilogy of the Ringworlds. That’ll be the day. 😎

              4. Yup. And it makes for great storytelling…but such a civilization would harness, proportionally, as much more energy than we do…as we do over the Neandertals. And, realistically, we have as much of a chance of accurately imagining what such a society would be like as a Neandertal would have had of imagining our society.


              5. “we have as much of a chance of accurately imagining what such a society would be like as a Neandertal would have had of imagining our society.”
                That’s why I plan to live forever. I want to actually know the future. I wonder if there’s a fast-forward button on this thing.

              6. Fast forward? Oh, that’s easy. Just build a spaceship that can travel a significant fraction of the speed of light and make a round trip.

                …of course, you’d need a sizable fraction of the energy output of the Sun to accelerate your ship to such speeds, such that only a civilization that can build Dyson Spheres can even think of launching such a ship, but that’s just an implementation detail….


    2. A grad student with $100 worth of stuff bought from the local hobby supply shop could do more science in an afternoon than all the robotic probes we’ve ever sent to Mars.

      Don’t get me worng; the work done by those robots is amazing and mind-blowing…but only because it’s frikkin’ science robots on Mars!

      Give a real geologist a shovel and an hammer and she’ll dig an hole deeper than the robots are tall in just an hour, for starters. She’d have all the most interesting samples laid out and organized, be able to make the assays and pick the ones best suited to microscopic analysis…for that matter, just feeling and smelling the samples would tell her all kinds of stuff right off the bat. And…Opportunity holds the distance record on Mars: in its entire lifetime, it hasn’t even made it as far as a single marathon. Especially in the low Martian gravity, our human geologist wouldn’t even blink at wandering to a site a few miles away, poking around, and getting back in time for dinner; that’d be a major months-long one-way excursion for Opportunity.

      The only advantage robots have is that they’re dirt cheap compared to humans. A manned mission to Mars is going to cost us more than all the robotic missions ever sent, combined…and then maybe even an order of magnitude on top of that, if we really want to do it right.


      1. In the long run, robots will win. I say, like 1000+ years. Robots can build robots 24/7 and even if not super smart, they will turn Mars into a shell if needed to find organic matter. Awaiting these future innovations, humans are still a lot better now.

          1. There will probably be another age of slavery. Some robots working for us and other robots working for robots and then robots working for no one. And then a whole bunch of Marvins exclaiming “It’s all so depressing.”

  8. Speculation of course but we need to do some serious thinking. The assumption seems to be that Mars is ours for the taking to manipulate as we will. But what if we did find even a rudimentary but functioning eco-system on Mars? Even leaving aside such semi-hysterical proposals as nuking Mars’ polar icecaps, do we have the right to remake Mars in our own image?

    I fully support our unpeopled robotic exploration of every nook and cranny in our solar system. But I’ve gradually come to the conclusion that a hummanned mission to Mars would be a colossal misapplication of resources for the foreseeable future. We need to invest our time and money in energy research. We need to build a sustainable civilization. Our future is here. To tell people that colonization of Mars is a serious solution to the spoiling of our own planet is simply immoral.

    Perhaps the first qualification for becoming an interplanetary species is getting our own house in order?

      1. Just a note. H. erectus became 2 million years, a mammal average I think. H. sapiens is already 0.5 – 0.8 Myrs old, if the new sequencing work is correct. (The H. heidelbergiensis sequencing from Sima de los Huesos.)

        So not “millions” of years perhaps. But we may want to have descendants…

      2. Erm…no.

        Antarctica is a luxurious paradise compared to Mars. Nothing we could even hypothetically do to Earth, not even global thermonuclear war, could render Earth anywhere near as inhospitable as Mars. Not even the comet impact that took out the dinosaurs…even several of those at once, and the Earth would still be heaven compared to Mars.

        If we could colonize Mars, we could just as easily colonize the asteroids. And if you can do that, there’s nothing a planet can offer that’s worth the price it takes to haul stuff up and down that gravity well.

        And don’t think about “terraforming,” either. Again, anything we might do to Earth, it’d still be far cheaper to fix Earth than to make a new one on Mars. Orders of magnitude — several orders of magnitude.

        Even overpopulation isn’t a reason to go to Mars. It’d be cheaper to riddle the Moon with underground tunnel cities than to ship people all the way to Mars…and the cubic volume of the Moon is vast compared to the square footage of the surface of Mars. And transporting people from Earth to anywhere else? Forget it…if we had the energy reserves to do that, we wouldn’t need to do it in the first place.



        1. I totally agree. For that matter, what’s the big hype for Mars colonization about anyway? Why not colonize the moon? 175x closer and Earth could provide resupply water.

    1. See my comment above on why the cost argument is nontrivial.

      And the “have to choose” argument is just erroneous. Science is mutually reinforcing, and we should look for the best solution.

      Finally, the colonizers do not ” tell people that colonization of Mars is a serious solution to the spoiling of our own planet”, it is those who oppose them who do. Aldrin, Zubrin, Musk et cetera all talk about risk management (having more baskets for eggs), responsible such, not about avoiding responsibility.

      1. Oy. I meant that people who do not like manned missions propose that such an argument (“tell people that colonization of Mars is a serious solution to the spoiling of our own planet”), is circulating. If it is, it is theirs. =D

  9. I do not think it likely that Mars evolved it’s own life. At least not beyond a very primitive pre-cellular type, which might be nearly impossible to find. The reason is the history of life on Earth was so serendipitous. It was a billion years between major advances in complexity. Primitive bacteria lived for a billion years before photosynthesis and Eukaryota emerged. This means it’s hard and chancy to get life to evolve on a planet.
    My guess is if there ever was or is life on Mars, it was delivered there from Earth and will resemble our own form: DNA. If so, it will be difficult to differentiate Martian life from Earth life until it is carefully sequenced and placed into the continuum of life on Earth.

    1. I don’t think you can have life without some form of cellular (or reactor) basis due to the dilution of replicator strands. Both “soup” and “battery” theories are based on cells.

      I don’t think life history on Earth was “serendipitous”, and I think the term you want is “contingent”. You can’t use billions of years of evolution as an argument against its possibility.

      More pertinent, life is unavoidable in battery theory, and the speed with which it appeared on Earth tests that well. The fossil evidence peters out at 1 billion year after planet formation, but it is enough to make that analysis. But Earth was habitable more than 4,3 billion years ago [ http://www.minsocam.org/msa/ammin/toc/2015/open_access/AM100P1355.pdf ], and the first divergencies looks to have happened over 4.2 billion years ago [ http://www.timetree.org/search/pairwise/2/2157 ].

      1. I’ll check out your links, thanks.
        “You can’t use billions of years of evolution as an argument against its possibility.”

        I think you can say something about it’s probability. If every major advance in life’s complexity takes a billion years, it says these transformations are rare events.
        There is a time window within which rare events have to occur to make it likely to advance. Meteor bombardment, ice ages, planetary tilt, and so on are all factors. So, on Earth, given simple bacteria, it was not inevitable that life became eukaryotic. Given a billion years it did, in fact, arise, but the only thing we can say about Mars is that it might have had appropriate conditions for some period of time, but we know it’s history was probably considerably different that on Earth. So, sure it is possible, given enough time, but the rarity on Earth suggests at least the same rarity on Mars. For complex life to have occurred once in a single solar system is pretty amazing. For it to have happened twice in the same solar system is doubly amazing, and therefore less probable.
        Now, I’ll read the links and see if I change my guess.

        1. “If every major advance in life’s complexity takes a billion years, it says these transformations are rare events.”

          I don’t think so. If it takes a billion years of photosynthesis to saturate the geochemical oxygen sinks before free oxygen can build up in the atmosphere, that tells us nothing about the rarity of aerobic metabolism. On the contrary, it seems that eukaryotic life emerged about as soon as it was energetically feasible.

          1. I agree with your point, but it doesn’t counteract my own. It took 4.5 billion years of geological and biological events to create our modern biotic diversity. Either the chemical reactions are rare or the geological conditions are not right for long intervals. That makes life as a planetary project rare overall. We could say that it almost didn’t happen on Earth. Meteor/cometary impacts, snowball-Earth events, original chemical conditions, all had to combine to promote life. The fact is that if we had a twin Earth orbiting opposite our Earth the chance of independent life flourishing on that twin would be very iffy. Now we are talking about a planet, Mars, with vastly different conditions. Periods of a billion years under appropriate conditions clearly did not exist as they did on Earth. How much more unlikely is it that life managed to thrive there? I’d say the chances are much less – even though not impossible.
            One scenario to consider – assuming life on Earth started and made some first steps in mid-oceanic ridges. The black smokers on the ocean floor arise from tectonic behavior. I’d have to guess that Mars did not have a similar past based on it’s smaller size. How long did oceans last on Mars? If there were tectonic fissures, did they last long enough for development to take place? I’m doubtful that conditions would have been similar enough.

      2. OK, looking at the papers, which are over my level of expertise to follow in any detail, it seems they support your statement that life on Earth began early. Soon after the conditions were right for life. OK. That’s reasonable. But I’m not sure it makes too much difference to my argument. Yes, if life started in the first hundred million years or so after the crust cooled, it means that the origin of life was more probable. So, on Mars, life of the same general form might have arisen in the same time frame. But it doesn’t really tell us how likely it was. It might indicate that if it happened here it could have happened there. We are still left with all the contingencies which lead to more complex forms. How long did Mars remain in a condition appropriate for life’s furtherance? An escaping atmosphere, cooler temperatures, dryer, etc. We do know that it no longer resembles the Earth. Their histories were very different. And it’s pretty clear that Mars was not as suitable as the Earth for life’s flourishing. Thus, my guess is, it was much less probable – though clearly not impossible.

      3. But why can’t you use billions of years of life’s flourishing without life starting again as evidence of the infinitesimal probability of life arising, if not implausibility?

        1. Because the presence of already existing life actively prevents the sort of prebiotic chemical evolution that led to the initial origin of life. Where in the living world is there room for a pool of nonliving primordial soup to sit undisturbed for the necessary millions of years?

  10. Here’s what it means:

    The science of exobiology has something in common with theology in that they are both “subjects without objects” – they have nothing to study and can only speculate.

    This discovery means that in the foreseeable future, theology might find itself alone in this respect.

    1. There’s a big difference, though. AFAIK xenobiologists try to develop testable measures (for their various hypotheses), try to assess how we might identify life from the data we already collect, and when they think we can’t, they think about what sort of future experiments we could do to collect the data they think we do need (to detect life). An example of testable factors is significant amounts of oxygen in an exoplanet atmosphere. Does that indicate life? Can we do it? Should we try to do it in future experiments? What accuracy and precision re: atmospheric composition would we need to infer life?
      This focus on identifying testable measures for its hypothetical subject make it more properly a science. You don’t see a theologian arguing that we should put a new detector in/on a telescope in order to test his hypothesis about God.

      1. “There’s a big difference, though.”

        Yes. In fact, there are quite a few big differences. I only stated that they have that one thing in common.

        It’s like if I said Democrats and Republicans have something in common in that both sides are happy that Kim Davis switched to the Republican party, that certainly doesn’t mean that Democrats and Republicans are the same.

        1. Oh, please! The area has a name, it is astrobiology. [ https://en.wikipedia.org/wiki/Astrobiology ]

          If you knew anything about the subject you would know that they have at two whole inhabited worlds to study – the Hadean/Archean “world” (used to study other climate regimes et cetera) and the Proterozoic Earth are both case studies. Open any astrobiology textbook, and the dominant part covers Earth.

          In that sense astrobiology is “more” than biology, planetary sciences, astronomy and cosmology, it has parts of all. But that is of course not enough, we need theories and their testing.

          Well, the area has two major theories since the 80’s, when “battery” theory joined classic “soup” theory. Seems the field took off from there, this year saw the Astrobiology 2015 conference has a first session on testing.

          This means as far as I can see that astrobiology has joined the rest of sciences as normal science. Nothing is lacking, nothing stands out – ask physicists if they have decided between particles or strings all the way down.

          And just when I want everyone to start shout this from the top of the roofs, I have to read this opinion. Oh well, at least it suggests the same thing, sort of.

          1. No, I read the same Wikipedia article that you just linked to before I wrote that post, and now I wonder if you read it yourself. It says this:

            “(The term exobiology is similar but more specific—it covers the search for life beyond Earth, and the effects of extraterrestrial environments on living things.)”

            Based upon that, I specifically chose to use the more appropriate term, exobiology.

    2. Also, It strikes me that since we agree on theology, or even in Jerry’s version that theology is the study of other theologists sayings, astrobiology differ even in the absence of theory and testing.

      It is a basic observation that the forming Earth had no life, but now it has. That is the broadest object of its study, the emergence process we see happened.

  11. Cool, my favorite topic! (Astrobiology, not Mars.)

    I think Lakdawalla is over-hyping “hype”. It is trivially untrue, since most science press conferences reports progress. (Exceptions exist of course, see the “arsenic life” press conferences, but that was “dark biosphere” scientists hyping their unlikely hypothesis.) Surface liquids are rare, this is only the 5th planet that are known to have them. (If you count Io’s lava and Enceladus water spouts, with Earth’s oceans and Titan’s lakes.)

    And I think Lakdawalla misses the on putative extant life. Anything that demonstrates greater habitability ups the likelihoods, even if these brines are too cold and close to the surface. The same geophysics two meter down would make a significant difference for life and its detection.

    The increased habitability and the possibility that there is RSL a few km from Curiosity brings up the fact that clean rooms are extreme environments too. and the growth they find there and later on the crafts are mostly extremophiles I think. We select for what we don’t want to bring.

    I can’t say I agree with Billings that people can dismiss, dodge or downplay planetary protection issues. [ http://www.nature.com/news/why-hunting-for-life-in-martian-water-will-be-a-tricky-task-1.18450 ] Earth is a bad case study in this respect and invading populations seem ubiquitous, but are in fact having a hard time doing so If I understand correctly!? “think of all the island species on our planet wiped out by colonizers” is a good point, I hadn’t digested that much.

    More compelling is the case of experiment contamination – especially early such – but if there is a martian biosphere it should be productive enough to eventually admit detection anyway. I agree with Jerry here.

    If we are going to explore or colonize these worlds, we are going to establish our own ecologies on some. Nothing new there, it has always been so, especially after we started domesticating plants and animals.

    what we see on Mars are only sort-of-similar rock structures

    To be clear, the detection suite consists of three macroscale components, of which (unique)morphology is but one. Those are strong constraints. But the rest of the suite is microscale, which necessitates sample return. The detection is incomplete and ambiguous.

    1. Do we really have to take contamination so seriously? What’s the worst thing that would happen if we sent a probe with nothing more than 1000 types of funguses and bacteria and microbes and whatever jobbers astrobiologists would choose and put them on the surface of Mars to let them wander or perish. It’s life! Let me them work it out and we can watch. That’s what I call terraforming with evolution.

    1. “NASA has been corrupted by the current regime. Don’t know how long it’s going to take, but this news that there is flowing water on Mars is somehow going to find its way into a technique to advance the leftist agenda.”

      Ow ow ow ow no no ow ow ow

      1. Given what the guy says, this is actually trivial, because “anything that people do that I don’t like” can be called “leftist”. It is a stipulative definition, remember? 😉

  12. I was fortunate, through dumb luck of working in the right place at the right time, to have designed and built one of the valves that made up the TEGA instrument which in 2008 confirmed water in the soil (but not flowing water as today’s announcement).

    The thank you plaque I got from NASA is probablly my favorite momento.

  13. According to what I read in one of Nick Lane’s books, there are some decent reasons to believe that the structure of RNA/DNA, and even parts of the genetic code, aren’t as contingent as we like to believe. They might be inevitable.

    So Mars life based on DNA would not be outrageously improbable, nor would big similarities in the genetic code. But there should definitely be a number of major differences.

  14. Jerry wrote:
    “That includes the similarity of the genetic code, the use of L-amino acids, and the similarity of gene sequences among diverse species. Presumably if we found Earth-derived microbes on Mars, their DNA—and again, Mars-evolved life probably wouldn’t even contain DNA as we know it”

    I disagree with this statement. My own professional assessment of astrobiology is that if Mars evolved life, it would almost certainly be DNA/RNA-based. Why? Two chemistry arguments: 1) availability of starting materials (self-replicators can’t form without abundant and spontaneously-formed, abiotic precursor chemicals around) and 2) template-directed, self-replicating molecular systems are virtually unknown. I seriously doubt whether there are other “solutions” to the problem.

    Naturally DNA/RNA-based Mars life would have completely different downstream machinery than on Earth?

    1. I completely agree with your points 1) and 2). I am a chemist by training and reached those conclusions myself, with the same “chemical logic”. Do we know if Mars has, or had, sufficient nitrogen, oxygen, phosphorous, etc. to make the necessary precursor chemicals? Chemical energetics, water as a solvent, and UV light as an activator, should lead down the same path as happened on Earth. However, if the starting “soup” is different, it is very possible that no self-replicator ever got synthesized on Mars.

  15. Until “we” refine the Goldilocks hypothesis to include the extremes of all relevant factors, we are doomed to speculate until Hell freezes over.

    I proposed that the Encyclopedia of Life (EOL) take on the chore of being a central repository (data bank and programs to massage the data) for tolerance ranges a few years ago, but flaked out on them because of personal distractions. My bad. I hope someone will take up the cause soon; it’s too big a job for me.

    “Places” in the sense of habitat are incidental to the complex of factors that are required for the existence of life (and, for that matter, the absence of life, e.g., toxicity).

    At present, so far as I am aware, such measures of relevant factors do not exist in complete and comprehensive form (not that that is a requirement before we can begin to use the information) beyond isolated studies. Such a system would provide a template for “automatically” reporting the data upon publication, even if incomplete–the very incompleteness becomes a value of a sort.

    But once we have even a modest collection of the parameters for various life, especially “extremophiles,” we will be able to approach these questions in a disciplined, truly scientific way. At some level the data and the programs developed for its analysis should be able to make predictions that can be tested.


  16. Great thought piece and discussion following it! Thank you Jerry, and all informed contributors, who I hope are not yet finished commenting!

Leave a Reply