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By Emily Lakdawalla

Europlanet : Life's a bleach

Aug. 24, 2007 | 08:30 PDT | 15:30 UTC

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by Doug Ellison in Potsdam

Just another paper in another session at Europlanet, not even a long presentation at 15 minutes, and not in the main conference hall. I counted just 27 people in the room - but apart from the stunning Uranus ring crossing images, it's probably the paper that will get the most media coverage. I'm going to tell you what was in his talk, tell you about the questions and answers, and give some closing thoughts. Sit down, get comfy, here we go:

Firstly - take a look at the abstract - it's probably the most verbose and detailed of the whole conference PDF link Also - media reports that described the work of Joop and Dirk as being non-peer reviewed are not true. They have a paper in the International Journal of Astrobiology (recieved November 2006, accepted March 2007) I know - because I have a copy in front of me.

Here's what Joop had to say. The hypothesis is fairly speculative, and is less about what he thinks is on Mars, and more about what might be on Mars. The issue with going and looking for life on Mars is that it takes many years for one instrument's discovery to then be interpreted, a new mission designed, and the follow-on to occur. What they've done with this research is try to figure out one way in which the presence of biological material on the surface could explain the Viking results.

Click to enlarge >

Viking lander
Credit: NASA

Extremophiles on Earth have a precarious existence because, to them, normality is 'extreme.' Atmospheric oxygen or any sort of material or biology from outside their niche could kill them. What we call an extremophile by Earth standards would be a normophile by martian standards and thus the entire planet is the ‘niche' and is exceptionally well isolated from outside influences.

The crux of the their research is that a 61.2 percent (by weight) mix of water and Hydrogen Peroxide (H₂O₂) has a freezing point of -56.5 degrees Celsius. Such a mix tends to super-cool, i.e. it doesn't tend to crystallize when it goes below freezing point. It is also hygroscopic, that is to say it will attract water from the unsaturated atmosphere, ice, or adsorbed water on mineral grains. We generally think of H₂O₂ as a bleach, a means to disinfect things - but it is to be found in natural history on Earth. There is a 1-centimeter-long beetle called Brachinux crepitans which produces a 25% H₂O₂ mix which reacts hypergolically with other organic material to form a shooting vent of steam to warn off predators. H₂O₂ should not be considered incompatible with biology - a Martian microbial life form that uses H₂O₂ is at least plausible.

Looking at Viking results, the GCMS (Gas chromatography mass spectrometer) did not detect any organic molecules, but it has been suggested that the sensitivity of the instrument was not sufficient to detect it. To date, no purely chemical explanation for the results of the Viking experiments has been found, nor is there an explanation for the Gas Exchange Experiment, which released CO₂, N₂ and O₂. The same is true of the Pyrolitic Release experiment which broke down organic material and the Labeled Release experiment of Gil Levin.

Click to enlarge >

Frost at the Viking 2 Lander site
Viking 2 landed far enough north that winter brought occasional frost to its landing site. This image was captured almost a full Martian year after Viking 2's landing, on May 18, 1979.
Credit: NASA / JPL

So - IF martian life is based on a mixture of H₂O and H₂O₂ as an intracellular fluid, it would scavenge water from the atmosphere. However, and here's the problem with the Viking experiment, heating it would lead it to self-oxidize, releasing excess oxygen, and pyrolysis could have resulted in CO₂, H₂O, N₂, and little else (as seen with Gas Exchange Experiment) In the case of the GCMS, the introduction of water would have essentially drowned the microbes, causing them to decompose.

If one assumes that biology is involved, with an intracellular solvent of 50% H₂O₂ and 50% H₂O, the result is that the biological material is 83% solvent and 17% organic macromolecules that would have been at a level within a soil sample of around 1,300 parts per million - 0.13%.

Could a future mission detect this kind of life? The problem is that detection of H₂O₂ - H₂O based life would be hard. Increase the temperature by a little, or add too much water, and you'll kill it. Decomposition of these organisms would be exothermic, which might be detectable by Phoenix. If the organisms are to be kept alive, you have to keep the experiments dry and sub-zero. And sample return would be hard because it's quite likely that during transit to earth the organisms would decompose to CO₂, O₂, H₂O, and N₂. However, freezing samples in liquid nitrogen might preserve them.

So then it was open to questions. The first was how they might get an energy source. Joop replied that he thinks it could be photosynthesis - but another audience member replied that there was no difference in experiments onboard Viking when conducted with and without light sources (he didn't reply to this, but I would assume the warmth of the interior of the Viking spacecraft would cause the microbes to be dead before such an experiment had taken place).

I then asked about the boiling point of the H₂O₂ - H₂O mixture. He said that H₂O₂ boils at 150 degrees centigrade - ‘what about at 6 millibars - Mars atmospheric pressure' I replied, citing the Mini-TES measurements of the near-equatorial Mars that Spirit and Opportunity have taken that show the surface temperature to exceed the boiling point of water at the air pressure present. ‘That's a good point' he conceded. He closed saying that it's just a hypothesis, it needs analysis - and it's a form of anticipation for what might be possible and thus the considerations we need to make when looking for life.

And now Doug's final thoughts. If there is life on Mars that uses H₂O₂ and H₂O as a cellular medium - then its unofficial biography makes frightening reading, as H₂O₂ is not nice stuff. There is a small group of scientists, and a slightly non-mainstream enthusiast group who believe that there is liquid water on the surface of Mars from time to time and that there can thus be life on the surface. But today we see a proposal for a life form that would infact be a contraindication for liquid water - or alternatively for which liquid water would be a contraindication - one would kill the other - as Joop says could happen in GCMS.

There is a strange circular line of thinking that one can follow. This theory is trying to answer the questions that remain over Viking instrument results, one of which is still maintained as a positive indicator for life by Gil Levin. Gil Levin's son was involved in the recent episode that involved a submission of a paper to a conference that claimed liquid water on the surface of Mars being imaged by Opportunity, which was rather rapidly torn to pieces when identified as being on a rather steep slope at Burns Cliff. But this biological hypothesis renders the liquid water briefly proposed by Levin an impossibility.

Click to enlarge >

Temperature of the Left Front Hazcam on Spirit
Temperatures in the shade for Spirit ranged from highs of about 35 degrees C. (95 degrees F.) in summer to lows of -90 degrees C. (-130 degrees F.) in winter.
Credit: NASA/JPL-Caltech/Cornell/NMMNH

I do not understand the physics involved in the behavior of an H₂O₂ - H₂O mix within a cell membrane. But we know that the surface of Mars for Spirit and Opportunity can swing from -90 degrees C to plus 35. Even with its tendency to super-cool, at 35 degrees below its freezing point, even the smallest nucleation point would surely cause freezing, such as the components within a cell membrane. And whilst it's contained - when the boiling point is reached, what would happen to the cell membrane? What sort of internal pressure would be generated, and how might it survive it? What about the contradiction between the suggestion of photosynthesis as an energy source and UV-rich Martian sunlight's ability to break down H₂O₂ or indeed H₂O₂'s reactivity with transition metals and specifically Fe²⁺ - the very element that makes Mars the colour it is. The media has picked up and run with this story much more than they responsibly should - had they taken the step of actually attending his talk they would have heard him say, quite clearly, that he is not saying this is actually happening, but that it is simply an hypothesis, it needs analysis, and is simply a set of potential considerations and anticipations in the search for life on Mars.

So there we go - the last paper I'm writing up on. It's been an astonishing week here in Potsdam. Somehow - I don't think I managed to cover as many papers as I did as well as I did in Valencia, but papers on scientific topics are harder to write than those of an engineering topic ( at least for me - happier with a screwdriver than a spectrometer ). I also had the added complication of having my own presentation to give - although on the upside that made it an easy one to write about and I think it went very well and hopefully made a few minds on this side of the Atlantic thing more seriously about doing as much for outreach as happens on the other side.

I hope you enjoyed reading at least some of it. There was so much I just didn't have the capacity to write down, such as a series of talks explaining the 0.2% risk of a damaging particle collision for the low Enceladus flyby for Cassini, and the 500 meter-per-second particles that have been calculated to be shooting out of vents that are on the order of a few tens of centimeters wide. There were the brilliant mission proposals for small lunar orbiters that were just inspired in their ingenuity, and the instruments to go on them that would be a miracle of engineering. In the next 12 months we've got a hell of a lot of new science to look forward to, particularly with the beginnings of the second part of the armada to the Moon that we call the International Lunar Decade.

I have people to thank - (annoying, predictable and boring though it is to read). Alice Wessen for being brave enough to ask me to submit an abstract, Jean-Pierre Lebreton and the committee for being crazy enough to accept it, and Anita Heward for giving me a press pass so that I could get through the door. I also have to thank Alice, Kevin Hussey and his lovely wife Jan for putting up with a Brit and inviting me out for some lovely dinner...I didn't even know what Cambodian food WAS until last night! The biggest thank you has to go to the Planetary Society - Emily and Lou for having faith in me - I hope I've done OK.

So that's it - this is me signing off - all I've got left to do is think of a headline for this article - hmmm . ‘The Martian ‘L' word'....hmmm.... ‘Bleach Bugs'...nahhh.... Oh - I know......

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surface encounters

Hey very nice blog!!....I'm an instant fan, I have bookmarked you and I'll be checking back on a regular....See ya :)

#1 - Jstackhouse - 02/25/2010 - 08:57


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