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Into Europa’s Ocean

Europa continues to fascinate us with the possibility of a global ocean some 100 kilometers deep, a vast body containing two to three times the volume of all the liquid water on Earth. The big question has always been how thick the icy crust over this ocean might be, and we’ve looked closely at Richard Greenberg’s analysis, which shows surface features he believes can only be explained by interactions between the surface and the water, making for a thin crust of ice. See Unmasking Europa: Of Ice and Controversy for more, and ponder the prospects of getting some kind of future probe through a thin ice layer to explore the potentially habitable domain below.

Possible interactions between the surface and the ice are considered in a new paper by Mike Brown (Caltech) and Kevin Hand (JPL), one that makes the case that there are two ways of thinking about Europa. One is to see the Jovian moon purely as an ice shell upon which the bombardment of electrons and ions have created a chemical cycle. The other is to see it as a geologically active world with an internal ocean that affects what happens on the surface.

Just how much, in other words, does the chemistry of the internal ocean affect what we see from our spacecraft and telescopes? Brown and Hand now believe they can identify a chemical exchange between the ocean and the surface that we can analyze to learn more about both.

Using data from the Keck instrument on Mauna Kea, the researchers have used adaptive optics and spectroscopy to go far beyond what the instruments on the Galileo probe were able to tell us about Europa’s surface. Turning up in their results is a magnesium sulfate salt called epsomite. Magnesium could not be found on the surface unless it came from the ocean below, meaning that ocean water does make it through onto the surface, while surface materials get into ocean water. Says Brown:

“We now have evidence that Europa’s ocean is not isolated—that the ocean and the surface talk to each other and exchange chemicals. That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”


Image: Based on new evidence from Jupiter’s moon Europa, astronomers hypothesize that chloride salts bubble up from the icy moon’s global liquid ocean and reach the frozen surface where they are bombarded with sulfur from volcanoes on Jupiter’s innermost large moon, Io. The new findings propose answers to questions that have been debated since the days of NASA’s Voyager and Galileo missions. This illustration of Europa (foreground), Jupiter (right) and Io (middle) is an artist’s concept. Credit: NASA/JPL.

Because Europa is tidally locked to Jupiter, the same hemisphere always leads in its orbit around the planet, while the other always trails. The difference between the two is striking: While the leading hemisphere has a yellow tint, the trailing hemisphere is streaked with a red material that has been under study for many years. It is believed that volcanic sulfur from Io accumulates on Europa’s trailing hemisphere, existing there along with a substance other than water ice that Galileo could not identify. Keck’s OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS) turned out to be what was needed to map the distribution of water ice and home in on the other material.

It turns out that both hemispheres contain significant amounts of non-water ice, but on the trailing hemisphere Brown and Hand identified the spectral signature of magnesium sulfate. Interestingly, the magnesium sulfate does not itself appear to come from the ocean. Because it only appears on Europa’s trailing side, where Io’s sulfur is accumulating, the researchers surmise there is a magnesium-bearing mineral — probably magnesium chloride — everywhere on the moon that produces magnesium sulfate in the presence of sulfur. The same magnesium chloride might then make up the non-water ice detected on the leading hemisphere.

Europa’s ocean can be rich in sulfate or rich in chlorine, but Brown and Hand rule out a sulfate-rich ocean because magnesium sulfate only appears on the trailing hemisphere. This fits with other work Brown has done on Europa’s atmosphere, which identified atomic sodium and potassium as constituents. The researchers believe that sodium and potassium chlorides consistent with this atmosphere are the dominant salts on the surface of Europa. Their conclusion is that Europa’s is a chlorine-rich ocean with sodium and potassium present as chlorides. By this analysis it closely resembles Earth’s oceans. “If you could go swim down in the ocean of Europa and taste it, it would just taste like normal old salt,” Brown adds.

The paper is Brown and Hand, “Salts and radiation products on the surface of Europa,” in press at the Astrophysical Journal (preprint). More in this Keck Observatory news release.


Comments on this entry are closed.

  • Dmitri March 6, 2013, 18:54

    This is facinating how things come together over time. The news on Europa and freshly released Dr. James Garvin presentation for undergraduate students about our planetary backyard from 2010 is one of those moments.
    I advice to find 55 minutes for this. Totally worth it:
    * The Inner Solar System: Discovering Earth’s Neighborhood – http://www.youtube.com/watch?v=TeC8dzwrmyw

    So now it turns out detecting life on Europe is just a question of finding the thermal vent and cultivating the bacterias on a swab easy. Even if it turns negative or the bacterias don’t want infect us the way X-files producers imagined or something other rather dissapointing I still wonder when the next interplanetary shuttle departs? There is so many geological features what could be explored by tourists.

    1) When Stanley Kurick made his 2001: A Space Odyssey he probably didn’t suspect that the monolith actually exists!
    * One on Mars – http://www.nbcnews.com/id/47024373/ns/technology_and_science-science/

    * The other on Mars moon Phobos – http://en.wikipedia.org/wiki/Phobos_monolith

    2) The well known Face on Mars, which is now refuted as optical illusion, actually exists! This time on Moon – http://phys.org/news/2012-02-face-to-face-shattered-lunar-boulders.html

    3) The beloved Disney’s heffalump Heffridge Trumpler Brompet Heffalump, IV is not a fictional character. It’s an actual feature on Mars – http://newsfeed.time.com/2012/04/09/an-elephant-on-mars-at-least-according-to-this-nasa-photo/

    Space is stranger than fiction!

  • Astronist March 6, 2013, 20:22

    We are talking about interactions between the surface and the subsurface ocean, but are these one-way or two-way? I can easily see water erupting out onto the surface, and thus bringing up samples of what is below for us to find. But the question that interests me is how much surface material is subducted and makes its way down into the ocean. Does anyone have any views on this?


  • Sedjak March 7, 2013, 1:25

    Discover Magazine recently had a colorful article on this topic:


    — Frozen. Irradiated. Desolate. Alive? —

    A rebellious young scientist
    makes the case that Jupiter’s icy moon
    Europa could host thriving life.

    “…(Britney) Schmidt had shown that they (lakes) could subsist just a mile or two beneath the Europan surface, shallow enough that scientists could plausibly imagine drilling through the ice and accessing them. These lakes could also be hotbeds for life, since molecules embedded in surface ice could easily get dumped into the water when the ice collapses…

    Her real breakthrough is finding the mechanism by which molecules on Europa’s surface could unite with water and energy in the lakes, and maybe even in the vast, deeper ocean…

    ‘We’re basically implying the ice is like a washing machine, mixing all those ingredients together,’ Schmidt says. ‘It gets me and a lot of other people really excited.'”

  • GaryChurch March 7, 2013, 2:12

    At least I know how to SCUBA dive. I can paraglide also.

  • Michael March 7, 2013, 12:56

    There exists a possiblity that small or large bolders left over from impacts on the moons surface will offer a mineral resource/organics and melting point lower chemicals to organisms in the ice covering at all depths.

  • Dmitri March 7, 2013, 16:21

    There is a good chance that Titan will throw next surprise as Cassini has already shown data which they try to model and probably it means there is a liquid ocean under the crust. But the crust is thick – 30 km.

    Liquid ocean might answer to question where Titan gets its atmospheric nitrogen. Also Titan’s atmosphere is suitable for forming complex amino acids.


    These findings of liquid recalls that Moon has liquid core as well. Which is rather surprising as it should be a dead heavenly body. Moonquakes still happen there.


  • Dmitri March 7, 2013, 16:33

    This is addition to previous Titan ocean research:


  • Dmitri March 7, 2013, 17:11

    Lake Vostok has revieled its first discovery of a microbe whose DNA resemblance is 86%. They can’t identify it and new samples will be taken in May to verify it’s actually a new life form on Earth.


  • Enzo March 7, 2013, 17:42

    There’s also a SETI Talk on Youtube from Britney Schmidt :

    SETI talks used to be HD (720p and 1080p) but no longer. Now it’s hard to read some graphs sometimes. It’s really annoying when something nice gets degraded like this. I wonder what’s the reason.

    Currently there is no budget for the foreseeable future for an Europa mission because the $1-2 B cost is way over the cap of the Discovery ($425M) and New Frontiers ($700M) caps. It’s all gone to Mars ($5B recently) .
    Hopefully the two flybys from EAS’s JUICE in 20131 will manage to determine how thick is the crust. Apparently the ice penetrating RADAR should get down to 9 km.

  • Dmitri March 8, 2013, 1:59

    @Enzo – Google+ Hangout is low resolution video that’s why you don’t have 720/1080. Also look at the view count – it’s always missing.

    Actually the thickness of Titan layers varies based on better telemetry and successes in modeling the data. Results by last December showed the core is around 2000 km, the crust 200 km thick and ocean around 125 km deep. Titan might have active cryovolcanism, at least a volcano has been discovered on it’s surfaces and the ocean deep below is considered as main source for the nitrogen-rich atmosphere. Don’t take the data as final it’s subject to constant improvements.


    Cassini is the proof what a satellite around a planet is good for. We don’t know much about Europa crust thickness.

  • Astronist March 8, 2013, 7:13

    @ Sedjak: “molecules embedded in surface ice could easily get dumped into the water when the ice collapses…” — I don’t buy it. Ice floats.

    @ Michael: yes, maybe large impacts could penetrate a km-thick ice crust. Good point.


  • Sedjak March 8, 2013, 12:09


    Its counter-intuitive to be sure, but Schmidt shows the dynamics of her process especially in the later part of the detailed youtube video presentation mentioned above. Also, Europa is a very active body as evidenced by its surface, by tidal heating and warping, posited sub-sea volcanoes, etc. Who really knows how water behaves under such extremes of low temps and high pressures? Maybe water seeking less pressure upward trumps the density issue under these conditions. We will have to wait until the next probes get there to be sure.

  • andy March 8, 2013, 13:58

    I came across this story on Mike Brown’s blog which he has recently ended a hiatus.

    Sea Salt (part 1)
    Sea Salt (part 2)
    Sea Salt (part 3)

  • GaryChurch March 9, 2013, 0:10

    Europa is the stuff of science fiction dreams but because it is real we do not feel so amazed maybe. I have always been interested because of a paper I wrote in Junior High about Alvin discovering the first hydrothermal vent communities. That was in 1977, so I have been thinking about these alien underwater worlds for a few years.

    Could there be a race of intelligent creatures living in the subsurface ocean of an icy moon.? I give it a far better chance than bigfoot.

  • Dmitri March 12, 2013, 6:19

    NASA / ESA / Roskosmos are making efforts to send a unmanned probe to Jupiter’s moon Ganymede as the most likely candidate for life on other planets due to its magnetosphere. Wiki article claims the goal for launch in 2020, Russians say “in this decade”.

    So there are other target beside Mars.


  • GaryChurch March 13, 2013, 21:52

    Right on Dmitri!
    Ganymede is a far better destination than Mars. However, I would go with Callisto.
    I read Callisto was the only one of the four that was not in a heavy radiation band.

  • Dmitri March 14, 2013, 10:42

    More good news – ExoMars rover is saved. ESA and Roskosmos signed agreement of financing. Instead of Mars Science Orbiter 2016 will be launched Trace Gas Orbiter to track methane and select a suitable landind place. 2018 ExoMars will be launched. ExoMars will have 2 meter drill for deep soil samples. Looks like next decade will be intresting in terms of exoplanetary life detection.

  • Dmitri March 15, 2013, 18:18

    So, life is stranger than fiction. Of course all depends which life we talking about. If it goes with the pace as currently we just have to admit that life we’ll find every elswehere is or is not related to Earth or note. Even to those Earth life forms we are discovering right now.

    Deep below the sea bed crust, in the floor seddiment at 380m there are microbes who have evolved into another ecosystem and thrive there.

    Now the question who is actual alien on Earth?

    Microbes surviving deep inside oceanic crust
    Mark A. Lever, of the Department of BioScience at Aarhus University in Denmark and an international team of microbiologists drilled through the sea-bottom sediment and deep into the oceanic crust beneath to collect samples for various tests. The sediment depth at the drilling site was about 260 meters thick, and the team collected samples from about 350 to 580 meters deep into the basalt rock beneath, in a region known as the “dark biosphere.” The age of the rock was estimated at 3.5 million years The team ensured all their equipment was sterile to ensure the rock samples were uncontaminated. They also added marker chemicals to the fluid used in drilling, and later confirmed that while these chemicals were found on the rock sample surfaces, almost none found their way inside the rocks. They sterilized the outer surfaces before breaking the rock samples open. The researchers found microbe genes within the rock samples, and to determine if the genes were from living microorganisms or extinct species, they incubated the samples at 65 degrees C (the temperature of the location at which they were found) in water similar chemically to that in their native location, which is rich in chemicals but poor in oxygen. After two years (enough for the slow-growing microorganisms to re-establish themselves) they transferred samples to another container containing sterilized rocks and the same water. They incubated these samples for a further five years. The incubated samples began to produce methane and the carbon-13 concentration reduced, which showed that the microbes in the rock were alive. The scientists concluded the organisms were most likely deriving energy from chemical reactions taking place in the interfaces between the iron-laden rock and water. The chemical reactions produce hydrogen, which the microorganisms use to produce organic matter. Other microbes were identified, which survived by consuming sulfur. These processes of energy production are known as chemosynthesis. The findings suggest that the ecosystems in the oceanic crust are fundamentally different from other ecosystems in that their energy is derived ultimately from chemosynthesis rather than photosynthesis, which derives energy from light.

  • GaryChurch March 16, 2013, 21:14

    I believe it is really amazing that we have discovered evidence of these oceans under the icy moons of the outer planets. AFAIK no one predicted it in any sci-fi stories. That aquanauts and nuclear submarines may be the real space explorers that will be needed is both amusing and fascinating.

  • Dmitri March 17, 2013, 16:08

    Now turns out Mariana Trench is suitable for microbial life and they are thriving there. These conditions should very well suit under crust oceans of Titan, Europa, Ganimedes. It won’t get any better to discover them up there than deep below ouf feet.


  • GaryChurch March 19, 2013, 13:39

    “Now turns out Mariana Trench is suitable for microbial life-”

    I am hoping for self-aware giant octopi or something interesting. Perhaps an entire civilization that has spread to all the moons possessing subsurface oceans. And they have been waiting for us.

  • Dmitri March 20, 2013, 10:24

    If we could design and test a statellite which could at its orbit study Mariana Trench and alike places on earth with acceptable precision and scientifically needed details, then there is no better place to test like on Earth’s orbit, replicate and send out to the candiate moons.

    What Russians reproach for NASA’s Curiosity over ExoMars they don’t dig deep enough – 5 cm vs 2 meters. But better Cursioty on Mars than ExoMars still on Earth.

    More good news – seems that analyzing Enceladus’ ocean water is just a question of flying high around the moon and taking samples of its water jets. The salty ocean beneath the crust is half time warmer tha surroundings but yet cold enough – 185K or -93.5C or -135F.

    The other thing is Enceladus’ crust – can’t say why Britney Schmidt thinks Europe’s one is only 3km just on Enceladus it’s 10 km.

    It seems more and more that probably the question of finding microbial life in the solar system is not the one, rather the question is how much they all differ and is same.


  • william f collins April 1, 2013, 19:41

    I certainly hope that the crust of Europa is thin enough for future explorers to drill or laser an entry hole for a robotic submersible to lower itself into a supposed Europan/Euceladuan Ocean. Would the intense radiation that Jupiter emits make direct human exploration prohibitive?