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An Oxygen-Rich Europan Ocean?

Long-time Centauri Dreams readers already know of my admiration for Richard Greenberg’s work on Europa, admirably summarized in his 2008 title Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon (Copernicus). It’s a lively and challenging book, one which Greenberg used to take sharp issue with many of his colleagues, and although he played this aspect of the work down in a phone conversation when I reviewed the book, the animated back and forth makes for a fascinating look at how planetary science gets done.

In his book, Greenberg argues forcefully that the thickness of Europa’s ice is unlikely to be more than a few kilometers, and that its active resurfacing would make it possible for life-forms below the ice to occasionally be carried above it. That would be good news for our hopes of detecting life, of course, for it would obviate the need to drill through the ice sheet. A spacecraft’s electronics might not last long given radiation levels this close to Jupiter, but probably long enough to make that kind of identification, if such is indeed possible.

Image: View of a small region of the thin, disrupted, ice crust in the Conamara region of Jupiter’s moon Europa showing the interplay of surface color with ice structures. The white and blue colors outline areas that have been blanketed by a fine dust of ice particles ejected at the time of formation of the large (26 kilometer in diameter) crater Pwyll some 1000 kilometers to the south. A few small craters of less than 500 meters or 547 yards in diameter can be seen associated with these regions. These were probably formed, at the same time as the blanketing occurred, by large, intact, blocks of ice thrown up in the impact explosion that formed Pwyll. The unblanketed surface has a reddish brown color that has been painted by mineral contaminants carried and spread by water vapor released from below the crust when it was disrupted. The original color of the icy surface was probably a deep blue color seen in large areas elsewhere on the moon. The colors in this picture have been enhanced for visibility. Credit: NASA/JPL/University of Arizona.

The tortured ice surrounding a distant Europan ridge, then, could be the venue for our first discovery of non-terrestrial life. The larger question is whether the ocean floor on Europa actually provides the conditions for life. Here the answer also ties in to that active resurfacing, one that leaves few impact craters intact and suggests that what we see from a spacecraft could be no older than 50 million years or so. Greenberg notes at the ongoing Division of Planetary Sciences meeting in Puerto Rico this week that cracks on the surface continually fill with fresh ice, while surface areas already in place are gradually replaced.

Add in mechanisms for gradually adding fresh material to the surface and you’ve exhausted the possibilities for resurfacing. But they’re all Greenberg needs to estimate that the delivery rate of oxidizers into the ocean is fast, so fast that the oxygen concentration of this sub-surface ocean could exceed that of Earth’s oceans in just a few million years. The upshot: This is enough oxygen to support not just micro-organisms but larger creatures, macrofauna whose metabolisms demand more oxygen.

And this is intriguing: Greenberg argues that it would have taken a couple of billion years for the first oxygen to reach the ocean. That delay could be crucial, for early organic structures could be disrupted by oxidation. On Earth, oxygen’s late arrival allowed life to go from pre-biotic chemistry to organisms that evolved to manage oxygen’s damaging effects. The same mechanism might have allowed creatures to emerge in Europa’s ocean.

We’re talking, remember, about a global body of water, one containing about twice the liquid water of all Earth’s oceans combined. If Greenberg is right, that ocean contains a hundred times more oxygen than previously estimated, allowing roughly 3 billion kilograms of macrofauna to subsist if their need for oxygen is roughly the same as we find in terrestrial fish.

Read Unmasking Europa for a close look at the Europan surface as seen through Voyager and Galileo imagery, the latter unfortunately compromised by the failure of the spacecraft’s high-gain antenna. Thin ice is a model supported by the imagery, and Greenberg goes on to discuss it in terms of the tidal forces acting on the moon. The case for thin ice is powerful, but we need new missions to nail it down, the first of which, the Europa Jupiter System Mission, won’t arrive any earlier than 2026.


Comments on this entry are closed.

  • andy October 8, 2009, 16:50

    Not that we’re likely to see what’s actually in the Europan ocean during our lifetimes… oh well.

  • Athena Andreadis October 8, 2009, 18:35

    Actually, oxygen did not mark or make possible the transition from pre-biotic chemistry to life. For millions of years, all earth organisms were anaerobic, and most of them are still around today (from Staphylococcus and Clostridium botulinum to several types of yeast). The advent of oxygen was a veritable holocaust, until cyanobacteria (previously known as blue green algae) figured out how to harness it by adopting and adapting chloroplasts. Excerpt on the topic from my book:

    “When oxygen first appeared on Earth it got equally bad press, and with good reason.
    At the molecular level we convert oxygen to carbon dioxide for fast, readily accessible energy (the production of oxygen by plants is another story, which we will look into in Chapter 6). We also use oxygen to make fire. But, as always, there is a price to pay for these pacts. Oxygen is actually not only flammable but poisonous, as every smith, shepherd, vintner or doctor can attest: it rusts metal, turns butter rancid, wine to vinegar and our brains to mush (hence the popularity of “antioxidants” with the natural vitamin crowd).
    What causes this Jekyll/Hyde split? Oxygen is potentially devastating because it easily loses an electron to become a free radical, as active and unpredictable as its political counterpart. By trying to regain its lost electron, the radical will grab it from anything nearby, starting a line of descendants, each of which can damage a biomolecule. To extract oxygen from the atmosphere and use it without expiring, terrestrial organisms have evolved a complicated chain of enzymes that handle oxygen as gingerly as World War II sappers manipulated armed bombs.”

  • Tom October 8, 2009, 19:44

    Perhaps more powerful than the case for thin ice is the biasing effect of interpreting what you want to see out of data. It is clear that Greenberg _wants_ the ice to be thin, but I still don’t see any evidence to suggest that. All the surface features tell us is that is was thin in the past.
    What we need is an impact crater from the last 1000 years.

  • ljk October 9, 2009, 10:40

    While searching for information on a flyby probe that could scoop up some of the debris from the plumes of Enceladus for return to Earth, I came across these interesting proposals for the robotic exploration of Jupiter’s smallest Galilean moon, Europa, which in turn could be used for Enceladus and other similar celestial places.

    Seismoball: A Small Europa Orbiter Drop-Off Probe for Early Exploration of the Europan Surface:



    Seismoball is very reminiscent of the American Ranger 3, 4, and 5 lunar probes from the early 1960s. These mechanical voyagers carried a seismometer encased in a large sphere made of balsa wood that would have cushioned the impact when the probe hit the Moon. Sadly none of them ever got to show their stuff, as Rangers 3 and 5 missed Earth’s natural satellite while Ranger 4 had major electronic problems and hit the lunar farside without returning any data (it was the first US probe to impact the Moon at least, FYI).

    It was thought that the sterilization process to keep terrestrial microbes from contaminating lunar bugs played havoc with the probes’ simple mechanical brains and kept them from performing what would have been a very interesting mission.

    NASA Jet Propulsion Laboratory Hydrothermal Vent Bio-sampler:


    Assessment of Alternate Europa Mission Architectures (NASA – January, 2008):


    Workshop Report on Ares V Solar System Science:


    This reminds me of the proposed uses for the Saturn 5 beyond sending humans to the Moon with Apollo. One plan was to put several big landers on Mars using the giant booster for a project named Voyager, which was later scaled back into what became known as Viking.

    Europa Ice Pick:


  • Doug M. October 9, 2009, 15:17

    Three billion kilograms is… pretty pathetic, actually.

    That’s three million tons, which is roughly the annual fish catch from the Mediterranean Sea. That sounds like a lot, but that’s just the fish that are caught in a single year. It’s on-the-order-of 1% of the macrolife biomass.

    1% of the biomass of the Mediterranean ecosystem is not likely to produce anything too impressive. I mean, yes, any life in Europa would be astonishing and wonderful. But it really sounds like we’re talking microbial here.

    Doug M.

  • ROCA October 11, 2009, 21:02

    I bought Richard Greenberg’s book and let’s wait until 2026!

  • amphiox October 12, 2009, 14:48

    Athena Andreadis: Did you misread the post, or am I misreading you? The argument is that it was the absence of oxygen not allowed for prebiotic chemistry to transition to life, and that the later appearance of oxygen allowed unicellular life to become multicellular, and that Europa, like earth, may have had a significant anoxic period in its prehistory, followed by subsequent oxygenation, raising the possibility for macrofauna to evolve there and be currently present.

    Doug M: It’s not exactly fair to be doing quantitative biomass comparisons between Europa and Earth, I think. Since our current assumption is that Earth is a well within the “goldilocks” ideal for a biosphere, and Europa sits on one of the extremes, a difference between the two of several orders of magnitude would be expected.

    (A bit of speculation, but if Europa really supported a total biomass equivalent to Earth’s, I’m guessing that we wouldn’t be having any debate right now about its habitability – we’d already know. Voyager would have snapped a picture of algae blooms along the crustal ice cracks, or some other evidence like that)

  • Tulse October 12, 2009, 23:50

    if Europa really supported a total biomass equivalent to Earth’s, I’m guessing that we wouldn’t be having any debate right now about its habitability – we’d already know. Voyager would have snapped a picture of algae blooms along the crustal ice cracks, or some other evidence like that

    Is undersea biomass obvious from satellite photos of the Arctic and Antarctic ice shelves? Presuming we exclude obvious fauna like penguins, seals and polar bears, could we spot sea-based life in the ice at the poles?

    I don’t know the actual answer, and I’ve always been curious in general just how easy it is to remotely identify life in the earth locations that are analogues to the various candidate spots for solar system life.

  • ljk October 13, 2009, 9:17

    Amphiox said:

    “(A bit of speculation, but if Europa really supported a total biomass equivalent to Earth’s, I’m guessing that we wouldn’t be having any debate right now about its habitability – we’d already know. Voyager would have snapped a picture of algae blooms along the crustal ice cracks, or some other evidence like that)”

    What is the color of algae when it is dead and dried?


    Now what is the primary color of all those llong ice cracks all over Europa’s surface?

  • ljk October 13, 2009, 9:30

    Monday, October 12, 2009


    ” . . . relay this information to Earth. Tsien destroyed three hours ago. I’m only survivor. Using my suit radio – no idea if it has enough range, but it’s the only chance. Please listen carefully. THERE IS LIFE ON EUROPA. I repeat: THERE IS LIFE ON EUROPA. . . ”

    ~ 2010: Odyssey Two by Arthur C. Clarke

    Europa, one of the Jupiter’s large moons, holds a special place in the minds of science fiction writers and astrobiologists alike. What sets Europa apart from the other planets and moons in our solar system is that it is covered with a fairly smooth surface layer of frozen water, and its interior is much hotter than its surface, suggesting that there could be a zone of liquid water under that protective layer of ice where life might exist.

    That easily accessible source of water on its surface could also make Europa a handy refueling stop for space ships exploring the outer solar system – assuming there isn’t the sort of life that destroyed the ill-fated spaceship Tsien in Clarke’s 2010.

    In the afterword to 2010, Arthur C. Clarke says his Europans were inspired in part by a 1980 article by Richard C. Hoagland – “The Europa Enigma” – which describes his “quite brilliant concept” that there might be life on Europa. Since then, NASA’s Galileo exploration mission to Jupiter and its moons has provided more detailed information about the moon’s surface:

    Prior to the Galileo mission, scientists’ knowledge of Europa was simply a small ice- covered moon with an exceptionally bright surface covered by faint curved and linear markings. Now, scientists see evidence of a young and thin, cracked and ruptured ice shell, probably moving slowly over the surface of a briny ocean that is 100 kilometers (62 miles) or more deep.

    University of Arizona Professor of Planetary Sciences Richard J. Greenberg, a member of the Galileo Imaging Team, believes that Europa might even be able to support fairly complex life forms, as Discovery News reported last week:

    Judging by how quickly Europa’s surface ice is replenished, Richard Greenberg estimates that enough oxygen reaches the subterranean ocean to sustain “macrofauna” — more complex, animal-like organisms. Assuming Europa life forms would need as much oxygen as Earth-like fish, Greenberg estimates the moon’s ocean has enough oxygen to support 6.6 billion pounds of macrofauna.

    Unconstrained by the limitations of biology, futurist/physicist Freeman Dyson has speculated a bit more wildly, suggesting that we should be looking for flowers on Europa’s surface:

    Life could be visible from orbiting spacecraft, however, if it made a home in cracks in Europa’s shell that connect the surface to the interior, Dyson said.

    Full article with lots of good relevant links here:


  • Adam October 15, 2009, 7:25

    Hi All

    Since Europa’s surface area is ~1.5% of Earth’s its size is about the size of the Mediterranean, so an apt comparison. Hard to imagine what sort of biosphere might arise and persist in such conditions, but at least oxygen isn’t an issue. Our failure of imagination – a common complaint of biologists about SF depictions of alien life apparently – is not a good guide to what we might find beneath the ice of Europa. Going and looking is what we do because we acknowledge the fatal short-coming of our imaginations… it isn’t real!

  • ljk November 29, 2009, 2:26

    Neutral particle release from Europa’s surface

    Authors: C. Plainaki, A. Milillo, A. Mura, S. Orsini, T. Cassidy

    (Submitted on 24 Nov 2009)

    Abstract: In this paper, we look at space weathering processes on the icy surface of Jupiter’s moon Europa. The heavy energetic ions of the Jovian plasma (H+, O+, S+, C+) can erode the surface of Europa via ion sputtering (IS), ejecting up to 1000 H2O molecules per ion and also break the chemical bonds of the ejected species which can result in the formation of new molecules (e.g. O2), a process called radiolysis.

    UV Photons impinging the Europa’s surface can also result in neutral atom release via photon stimulated desorption (PSD) and chemical change (photolysis).

    In this work, we study the efficiency of these two processes (IS and PSD) for ejecting water molecules. We simulated the resulting neutral H2O density, finding that they alone cannot sustain the tenuous atmosphere deduced from the Galileo Orbiter data. We also estimate the contribution to the total neutral atom release by the Ion Backscattering and Neutralization (IBSN) process.

    Moreover, we estimate the possibility of etecting the sputtered high energy atoms (SHEA), in order to distinguish the action of the IS process from other surface release mechanisms.

    Comments: 42 pages, 9 figures

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    Cite as: arXiv:0911.4602v1 [astro-ph.EP]

    Submission history

    From: Christina Plainaki [view email]

    [v1] Tue, 24 Nov 2009 11:25:35 GMT (889kb)


  • ljk December 17, 2009, 1:31

    December 16, 2009

    Could there be Life on Jupiter and Saturn’s Moons?

    Written by Nicholos Wethington

    The ongoing search for the existence of life that doesn’t call the Earth ‘home’ could potentially find that life right here in our own Solar System. There is considerable debate about whether evidence for that life has already been found on Mars, but astronomers might do well to look at other, more exotic locations in our neighborhood.

    At the recent meeting of the American Geophysical Union in San Fransisco, Francis Nimmo, who is a professor of Earth and planetary sciences at UC Santa Cruz, said that the conditions on Saturn’s moon Enceladus, and Jupiter’s moon Europa may be just right to harbor life.

    Nimmo said, “Liquid water is the one requirement for life that everyone can agree on.” The water underneath the icy crusts of Enceladus and Europa may just be teeming with alien fish and algae, or more basic forms of life such as bacteria.

    Nimmo is one of a long list of scientists speculating on the existence of life on these watery moons. A discovery of any life form originating from a planet other than the Earth “would be the scientific discovery of the millennium,” Nimmo said. And even saying that is an understatement

    Full article here:


  • ljk October 5, 2010, 7:52

    FEATURE / Europa’s Hidden Ice Chemistry

    The frigid ice of Jupiter’s moon Europa may be hiding more than a presumed ocean: it is likely the scene of some unexpectedly fast chemistry between water and sulfur dioxide at extremely cold temperatures. Although these molecules react easily as liquids—they are well-known ingredients of acid rain—Mark Loeffler and Reggie Hudson at NASA’s Goddard Space Flight Center in Greenbelt, Md., now report that they react as ices with surprising speed and high yield at temperatures hundreds of degrees below freezing.

    Because the reaction occurs without the aid of radiation, it could take place throughout Europa’s thick coating of ice—an outcome that would revamp current thinking about the chemistry and geology of this moon and perhaps others.

    FULL STORY: http://www.nasa.gov/topics/solarsystem/features/europa-ice.html

    CONTACT: Liz Zubritsky, Elizabeth.a.zubritsky@nasa.gov; Tel. 301-614-5438