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The Chemistry of Europa’s Ocean

The news that hydrogen peroxide is found across much of the surface of Europa is intriguing. The global ocean beneath the moon’s icy crust would turn hydrogen peroxide into oxygen, assuming there is some mixing between the surface and the ocean. We don’t know if that mixing occurs, but if it does, then we may be looking at a useful chemical energy source for life. Given that I spent much of last week writing about Arthur C. Clarke, this thought invariably brings up a recent viewing of 2010: Odyssey II and the injunction beamed to Earth: “All these worlds are yours except Europa. Attempt no landing there.”

Europa is increasingly irresistible the more we learn about it. Here’s Kevin Hand (Jet Propulsion Laboratory) on the question of hydrogen peroxide’s possible role:

“Life as we know it needs liquid water, elements like carbon, nitrogen, phosphorus and sulfur, and it needs some form of chemical or light energy to get the business of life done. Europa has the liquid water and elements, and we think that compounds like peroxide might be an important part of the energy requirement. The availability of oxidants like peroxide on Earth was a critical part of the rise of complex, multicellular life.”


Image: This color composite view combines violet, green, and infrared images of Jupiter’s intriguing moon, Europa, for a view of the moon in natural color (left) and in enhanced color designed to bring out subtle color differences in the surface (right). The bright white and bluish part of Europa’s surface is composed mostly of water ice, with very few non-ice materials. In contrast, the brownish mottled regions on the right side of the image may be covered by hydrated salts and an unknown red component. The yellowish mottled terrain on the left side of the image is caused by some other unknown component. Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. Credit: JPL.

Hand and Caltech’s Mike Brown went to work on Europa using near-infrared data from the Keck II instrument on Mauna Kea. The hydrogen peroxide they found is some 20 times more diluted than what you might buy at the local drugstore, and it’s unevenly distributed on the surface. Here it’s important to remember that Europa is locked to Jupiter — it rotates on its axis once for every 86 hour orbit around the planet — so its hemispheres keep the same orientation toward Jupiter and, importantly, the radiation environment in the magnetosphere. In terms of hydrogen peroxide, the highest concentration (0.12 percent relative to water) is to be found on the leading side; i.e., the side that leads in Europa’s orbit around Jupiter. The side that faces backward in the moon’s orbit shows a concentration of peroxide that drops off to close to zero.

The work also shows that peroxide is at its highest concentration in areas where the ice is nearly pure water, a fact discussed in the paper, which ran in Astrophysical Journal Letters. It was the Galileo mission that first detected hydrogen peroxide on Europa, and the new work adjusts our view of its distribution. In the passage below, NIMS refers to the Galileo spacecraft’s Near-Infrared Spectrometer, which made the hydrogen peroxide detection:

…we note that the radiolytic production of surface oxidants has long been of interest in the context of Europa’s subsurface ocean chemistry (Gaidos et al. 1999; Chyba 2000; Chyba & Hand 2001). If Europa’s oxidant laden surface ice mixes with the ocean water then radiolysis could be a key mechanism for maintaining a chemically-rich and potentially habitable ocean (Chyba 2000; Hand et al. 2009). Previous estimates all assumed a globally uniform layer of peroxide within the ice layer and calculated delivery rates based the NIMS concentration of 0.13% relative to water.

But now we learn that the distribution is not globally uniform:

Our new results indicate that only the most ice-rich regions of Europa reach the concentrations measured by NIMS. The trailing hemisphere concentration is nearly an order of magnitude lower than the leading hemisphere and the sub- and anti-Jovian hemispheres are down by a factor of ∼3 relative to the leading hemisphere. As a result, the average global surface abundance of peroxide in the surface ice of Europa may be better represented by the sub- and anti-Jovian hemisphere concentrations of ∼0.044%. This reduces the low-end estimate of Chyba & Hand (2001) from ∼ 109 moles per year peroxide delivered to the ocean to ∼ 108 moles per year delivered.

Given its importance for the habitability of the global ocean, the more we learn about hydrogen peroxide and its distribution, the better. We’re refining the Galileo results, but hampered by the lack of resources in the Jovian system — the paper goes on to point out that the cold water ice regions of the poles are not readily observable from Earth. But the work lowers our estimates of the total oxidants delivered to the ocean, assuming that there is indeed exchange of material between the surface ice and the water below. The case for a habitable ocean is still there to be made, but until we know more about delivery mechanisms, we’re left with huge imponderables.

The paper is Hand and Brown, “Keck II Observations of Hemispherical Differences in H2O2 on Europa,” Astrophysical Journal Letters 766 (2013), L21 (preprint). More in this JPL news release.


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  • Alex Tolley April 9, 2013, 10:01

    The availability of oxidants like peroxide on Earth was a critical part of the rise of complex, multicellular life.”

    Not really relevant. Earth started with anaerobes. The key issue is whether there is a proton gradient that can be exploited by chemistry.

    For life using oxidative processes, oxygen isn’t the only element that works. Sulphur works too. And Io is not far away…

  • ljk April 9, 2013, 13:36


    Brinicles and the Origin of Life

    The Physics ArXiv Blog

    April 9, 2013

    Extraordinary tubes of ice that grow down into the ocean from ice sheets could be as significant for the origin of life as hydrothermal vents, say chemists

    One of the more curious processes that occur beneath the Antarctic sea ice in winter is the formation of brinicles. These are hollow tubes of ice that project down from the ice pack into the sea below, like icicles.

    However, brinicles form in a very different way from icicles but are poorly understood, partly because of the difficulty in observing them. Indeed, they were only filmed forming in situ for the first time for the BBC documentary frozen planet which aired in 2011.

    Today, Julyan Cartwright at the University of Granada in Spain and a few pals hope to change that by examining the formation, chemistry and structure of brinicles in more detail. They say the structures are a special form of chemical system known as a chemical garden that depends crucially on the interplay between highly concentrated brine, water close to its freezing point and the formation of ice.

    But more interestingly, they say that brinicles may have played an important role in the origin of life on Earth and that similar structures elsewhere in the solar system could be equally important.

    Conventional chemical gardens are tubular structures that form when metal salt crystals are immersed in certain solutions.

    They occur in a number of natural situations such as in some geological formations and around hydrothermal vents.

    Usually, the tubular structures grow upwards. But in brinicles, the tubes grow downwards, so what gives?

    The effect occurs in the ice below the sea surface because brine has a lower freezing point then water. When trapped seawater freezes, it excludes salt increasing the salinity the brine nearby and lowering its freezing point even further.

    If the ice cracks, the trapped brine can leak into the sea below and flows downwards, because it is denser than water.

    What’s more, because it is so cold, the brine turns any seawater it meets into ice. That’s how the tubular structure forms and continues to grow as long as the brine flows.

    This process raises interesting questions for physicists. For example, the process by which ice rejects salt to increase the salinity of brine has interesting similarities to the process of osmosis in reverse.

    That’s important because reverse osmosis is the key process at work in the desalination plants that turn seawater into drinking water.

    It’s just possible that a better understanding of how brinicles perform the same process to produce pure ice could lead to better ways of doing this.

    But Cartwright and co’s most interesting observation is that brinicles also create chemical gradients, electric potentials and membranes–all the conditions necessary for the formation of life.

    Exactly the same conditions occur at hydrothermal vents which have been the focus of attention for many biologists wanting to better understand how life might have formed.

    The point that Cartwright and co-make is that brinicles can be just as interesting. “As brinicles play an important role in the dynamics of brine transport through sea ice, they might also play a role in this scenario of a cold origin of life, just as hydrothermal vents do in the hot environment theories,” they say.

    What’s more, brinicles could well be ubiquitous on ocean bearing planets and moons such as Europa, where they might play equally interesting roles.

    Clearly, a fascinating area where further work could be highly fruitful.

    Ref: http://arxiv.org/abs/1304.1774: Brinicles as a Case of Inverse Chemical Gardens

  • David A. Czuba April 9, 2013, 18:28

    A possible mechanism for delivering surface matter to subsurface water on Europa was posited by Britney Schmidt and others in an article by Gregory Mone in the Nov. 2012 Discover magazine, pp. 30-37. The essential theory says a sub-ice lake could render surface ice unstable, causing it to cave in. These unstable areas to convey surface material to depths over the millenia.

  • Rob Flores April 9, 2013, 18:54

    I think the biggest factor in potentially Europa having lifeforms is
    it’s relatively thin crust. This means that the debris of modestly sized
    asteroids <200m, can penetrate the surface layers. Manna from heaven
    to any lifeforms. It's closeness to Jupiter, keeps matter flowing in,
    and the Ice relatively thin.

  • Andrew W April 9, 2013, 19:03

    …10^8 moles per year…

    Is that 3,400 tonnes H2O2/yr?
    (I’m not a chemist)

  • Alex Tolley April 10, 2013, 11:12

    @Andrew – yep.

    Put in perspective. The mass of O2 in the earth’s atmosphere ~ 10^15 tonnes. Accumulated O2 liberated from the peroxide (if never lost) over 1 bn yrs would be ~ 3×10^12 tonnes 300x smaller. The surface area of Europa is ~ 5% of Earth, so the O2 on Europa has ~ 1% of the Earth equivalent per area. This seems to imply that either the O2 is very “dilute” in a rather deep Europan ocean to support aerobic life, or that it would need to be concentrated in pockets, perhaps under the surface ice, to support more energetic life.

  • Adam April 11, 2013, 16:06

    Alex Tolley, shouldn’t you compare against the oxygen that’s actually in the Earth’s ocean, rather than in the atmosphere?

  • Adam April 11, 2013, 16:22

    A quick look at the NOAA web-site and some O2 solubility tables in sea-water, I’d say roughly 7 mg/litre is a good estimate for Earth’s oceans. That means about 10 trillion tonnes O2 is dissolved in them. Europa’s area is 0.06 Earth so per unit area Europa has more oxygen than Earth’s oceans, though of course we don’t have tight constraints on the depth. Of course we have no idea how much oxygen is consumed in Europa’s ocean, so the present day levels would be anyone’s guess.

  • Rob Henry April 11, 2013, 22:05

    Some of the calculations here seem applied to strange ends: such as how Earth like could the oxygen content of the Europan ocean be if it was biologically and geochemical dead. I propose the following metric as far more interesting: how powerful can any ecosystem there be.

    At a quick calculation, 10^8 moles/yr of H2O2 oxidising dissolved ferrous ions to ferric ones, yields 0.02 W per Europan square kilometre. If it first breaks down to O2, this figure lowers to 0.01 W/sqkm, And that is ten million times lower than our oceans.

    On the positive side, this might be a boon for more complex plant life to evolve, there and follow the H2O2 depositing seams up. Perhaps that might be able to create biogeochemical cycles by such strategies that end up making the cycling of such materials from the surface orders of magnitude more rapid. That would make the above a gross underestimate and relatively more complex forms might dominate life. That’s asking too much though isn’t it?

  • Alex Tolley April 12, 2013, 0:06

    @Adam – good point.
    My BoE calcs (if correct) , using the 1bn year accumulation of peroxide in the ocean with no losses results in:
    1o mg/L for 10 km depth Europan ocean
    1 mg/L for 100 km
    10^-4 mg/L for 1000 km
    So possible, if the subsurface ocean depth is shallow and all the peroxide was cycled into the ocean and accumulated without loss. Lots of “ifs”. I still think sulphur meteorites from Io are more attractive as a oxidative element.

  • Dmitri April 12, 2013, 5:03

    I’m just wondering is manned mission to Europe possible with the current or feasible near-term technology? Maybe the radiation from Jupiter makes it impossible and leaves it only for robotic exploration.

  • ljk April 12, 2013, 9:48

    If you can burrow under the Europan ice that should make for some good radiation shielding. Assuming people want to live like that.

    The details of such an undertaking are here:


  • Alex Tolley April 12, 2013, 9:58

    @Rob Henry – you beat me to it. If there is aerobic life, it will be consuming the peroxide. Therefore the global “respiration” is just a few thousand tonnes/yr of new oxidant. Pitiful. (Could we even detect it?) If Europan life is aerobic (at this point I am not clear why it should be except that we only have aerobic complex life on earth), there needs to be some equivalent of O2 generating plant life. But this life would need to be able to work with some other energy source than sunlight. Now what would be fascinating is if CO2 fixation and O2 generation are not part of a coupled process like we have on earth. What if CO2 fixation was done by one type of organism, and O2 generation was a completely different process, possibly not even biogenic?

  • Rob Henry April 12, 2013, 20:29

    Alex Tolley et al.,I feel that other subtleties are being missed also.

    Hydrogen peroxide is not being created on its own, but along with reduced material, that may or may not be buried and subducted with it. If the predominant mechanism of production also creates reduced organics, then there may be very little potential for oxidation of the interior ocean, but the energy available for subsurface life may be similar. On the other hand H2O2 production may be predominantly accompanied by the release of H2 to the surface. This would be rapidly lost, and subduction processes would then be oxidizing the interior, irrespective of how that was being used by life. In this second case, free O2 buildup would be bad for an ecosystem, as it would imply that there is little left to oxidise, and that decomposition of H2O2 is all that is left for life to catalyse.

    Also note that if the surface crust was 0.13% H2O2 as originally thought, this shell would decompose in warm water to produce water that was ten times more oxygenated than Earth’s oceans (if Adam’s 7mg/litre is correct). Think of Europa’s entire crust at that level then suddenly melted. That is misleading of cause, as H2O2 is only created at the surface, and is only stable at low temperatures. To me, most of this crust would be cold enough for a H2O2/H2O mix to be stable. Here, we seem to have prima facie evidence that H2O2 is not stable in the presence of a common (reducing agent?, catalyst?) that is present in areas where water activity is lower.

    So, it is all very complex. We really need much modeling and additional information here.

  • william f collins April 13, 2013, 23:04

    Dmitri & Ijk
    The point about the intense Jovan radiation is a very important one. Although I imagine that if and when a robotic explorer (with a submersible attached) ever burrows through the mantle with an ocean beneath, the pressure to exam the possibility of manned expeditions to Europa might mount. On the other hand, if “Europans” are found by robotic explorers, a mature interplanetary civilization(us) might be content to observe and study such lifeforms from a distance using robots. Then again, it may be too dangerous for humans to even approach much less land on Europa.

  • Dmitri April 15, 2013, 13:58

    Thing that bothers most is a lack in hard SF reference to such manned mission. Arthur C. Clarke like contemporary visionary depiction of such possible undertaking. Clearly with the second wave of unmanned exploration we have made long strides in last 16 years – from microwave size Pathfinder to mini-truck size Curiosity. Yet even at this moment Curiosity won’t be able to answer is or is not life on Mars, unless it won’t bump into a clear fossilized evidence. Spirit and Opportunity proved beyond doubt viability of unmanned crafts, just involving humans tend to speed the pace up. Mix of such combined missions would better answer question is there fossilized / living evidence of biological lifeforms not mentioning advances in planetary geology. With mounting indirect evidence Europe being most likely place to go we don’t talk about manned one in 40-50 years time but take the JUICE mission like a godsend.

    Good that there is somehting on the subject. At least on some level somebody tries to play w/ the idea. Unmanned is always better than no mission.

  • Rob Henry April 15, 2013, 19:50

    UNLESS life with some very clever strategy for retaining a liquid intracellular interior exists within 100m or so of the surface and farms these chemicals THEN the maximum energy delivery should be the sum of the chemical energy of at the surface divided by the regional surface age. Here we are hoping that significant patches of surface exhibit both young age and high energy content.

    Estimates for biochemical energy available from hydrothermal vents total about 0.001 W per square km of lunar surface. This here seems about 0.01 W/sqkm as the minimum given by chemicals delivered to the ocean below IFF they are stable over their entire period of subduction. I would love to know what this says about their maximum estimate (for which the above calculation should be attempted), which was of the order of 1W/sqkm.

    By comparison, that reverse hydrogen flow data on Titan suggests the existence of an ecosystem whose minimum power is 20W/sqkm, and where the combination of very low surface levels of ultraviolet compared to visible light makes photosynthesis possible. To my mind, we need just a bit more before Europa gains primacy in a hunt for life in the outer solar system.

  • Alex Tolley April 15, 2013, 23:18

    @Dimitri – it is going to be very hard to do a manned mission to Europa. The radiation is lethal, so even approaching the moon is problematic. If you are hoping to find macro fossils on the surface, it is hard enough finding fossil beds on earth with many eyeballs, imagine how hard it would be on a such a different world. Most hopes for life is some sort of hydrothermal vent, which means drilling through kilometers of ice (extremely hard even for a small bore) and then submerging for maybe 100km in depth (which I calculate as having ~ 3x pressure as earth’s ocean floor). GaryChurch might have wanted to go scuba diving on Europa, but in practice I think we must consider robots for the foreseeable future.

    If we are going to explore Europa, especially regarding possible oceanic life, I would hope we could look for surface macro signs, the equivalent of stromatolites or iron banded rock on earth. That would seem to require a lot of high resolution imaging and then a surface probe. I would also want to look for possible very shallow ice or even a possible warm vent penetrating close to, or on the surface, that just requires relatively easy sample taking.

    I personally am very skeptical that there is Europan life. I don’t think the Earth model of vent life is appropriate, which also requires this location as the origin of life for Europa.

  • Dmitri April 19, 2013, 17:14

    @Rob Henry, you nailed it. NASA’s current agenda, after Viking’s failure to detect life directly, has shifted on geology and geological premise for life. This is the way to go. Life may or may not exist but geological features or records can tell the history. Yet it leaves to these kind of problems where you can’t say definitely of existance of current life activity. It’s like Venusians send a probe to Earth which land in bog and after analyzing dirt, soil and body of waters they assume the theory of pink aliens is plausable but not proved.

    In your opinion what is likelihood of finding any sign of microbial life under lakes of Antartica (Vostok, Ellsworth) based on availability of biochemical energy? These places might be the only closest model of Europe’s environment on Earth.

  • Dmitri April 19, 2013, 18:45

    @Alex Tolley I second. Every manned mission begins from mission goals. We have ventured far beyond the Cold Ward doctrine of reaching the goal by any means. Death or severy health danger for the crew is a definite no. Considering Jupiter is a not ignited star puts in perspective what dosages Jovian radiation emmits. Yet looking into past of human history there always been pioneers, futurists or lunatics depicting reality of tomorrow in a way which a week later seems like everyday routine. Jules Verne 1870 book 20 000 Leagues Under the Sea far before submarines were reality. Jacques Piccard 1960 and James Cameron 2012 are lunatics who had means to do something no one consider possible. Hillary and Tenzing claim to Everest. Franz Reichelt infamous jump from the Eiffel Tower which was tragedy at the time. Now mountaneering, jumping and freefall is a norm. There are things which become widespread when the means become financially accessable – not cheap, accessable. Even now 143 years after Julies Verne book building a submarine is considered doable for private corporation but still is regarded as a high technical achievement. That means w/o stimulating public vision who knows what we would have had by now but the general knowledge of technical challenges and mitigating them gives higher chance achieving progress in the submersibles field. Right now we are so content with the news from automated rovers and satellites up in space that most people don’t even pay attention. We are happy when automated stations looking far beyound the Solar system, even if some new unmanned craft is considered stay withing the Solar system it’s called achievement. What is missing is human involvement. Talking and proposing manned mission to speed up things, bring results closer and shortens disputes on theoretical models, which in total will move us forward. The question of existence of life beyound Earth is paramount. It has to be formulated on macro level (where to go) not micro (what suppose find). In the forum we make no deal of terraforming a planet yet a manned trip finds plenty of arguments what prevents it. It’s because we connect w/ the latter – comprehend, put in perspective, make it personal. Just for the sake not letting it happen in 143 yers later, 2156, but rather start to talk now and convince public w/ the idea doing it in feasible time – let’s say in 50 years. The NASA & Roscosmos announced manned mission, even SpaceX *commercial* roundtrip to Mars sounds now like a supersticion. It’s true the goal is unclear. It’s true there might be better candidates. It’s true that 50 years is a too short period considering technological shortcomings for such mission. The most important thing is to let the ball rolling and adjust its course when the real goal becomes clearer – it could be any destination, even Europe.

    Reason why at all we talk of manned mission is lack of a better substitude. Don’t have AI. Not even basic, self-sufficent one which would help send human-alike versatile bionic robot for dirty / dangerous work. Lack of radiation shielding technology material / EM / metamaterial based. Maybe the solution would be a cruise ship size personal EM radiation deflector which shields the crew or bionic workers AND the eqipment. Allows crew stay for a longer and divides the task over many iterations, even leaving the site or planet for a period. No current drilling technology suits such task. Maybe 3D printer producing nanoparticle size diggers which at depletion becomes part of the digged hole supporting wall.

    Don’t take this as call for the arms. Current discussion just made thnik on this. A descent hard SF story would outline proper base for this. The question of favorable geology and abundance of bioenergy will make or break interest for Europe.

    I personally would go for AI + bionic – makes the same minus the human losses.

  • Rob Henry April 19, 2013, 22:15

    Dmitri, I think that the prospect of finding unique low metabolism and sparse life in Lake Vostok is good. The prospect of finding truly unique forms there is more mixed. But I think that these prospects would have been far higher if very high energy chemicals, such as hydrogen peroxide, was flowing into them. That’s the pity!

  • Dmitri April 20, 2013, 15:19

    The Vostok team will return to the site in May to fetch a new batch of pure water sample. The news on finding a new bacterial form was retracted but it was done to fend off press interest. All the ones detected were considered contaminants except one. Yes, you can’t do far fetching conclusions based on one bacteria in sample and yes the count is exceptionaly low. By october or year end fresh news on Vostok should come in.

  • Dmitri April 24, 2013, 7:53

    Priceless joke. Valeriy Galchenko (Валерий Гальченко) the head of the Vostok project and principal microbiologist of the project mentioned in a TV interview @ 2nd March 2012.

    Many international teams have been interested to get hold of the Vostok samples on which he answered “The bride is already married”. Nice swipe. They do the project with annual budget $1mln. On cheap, say the least.

    Also on question is or is not life in Vostok he mentioned that there is no comparable analogy but in samples of some ice covered isolated shallow lakes on depths 2-6m below ice cover has shown existence on microbiology but only prokaryotes (no nucleus).

    In general the microbial concentration probably is very (very-very) low which gets its energy on methane, hydrogen sulfide and hydrogen from the crust and a lot (a lot – a lot) of oxygen from the ice sheet. The gases get oxidized and some kind of thermal vents are expected.

    Fresh news in a year or less than that.

  • Dmitri May 22, 2013, 2:08

    Either I’ve seen the future or someone has read my mind before I even thought about it. I’ll put this movie to my “must see” list. The lead role is by Sharlto Copley – Wikus Vand De Merwe of District 9.


  • Dmitri May 22, 2013, 2:17

    … and there is review of it before screening …. Pity it’s a horror movie.


  • Dmitri May 22, 2013, 2:26
  • Noel Shipman October 8, 2013, 14:23

    Life is probably under that ice.