by Alex Autin

Underground Sea Detected On Icy Enceladus

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Saturn’s icy moon, Enceladus, is one of the brightest objects in our solar system. Covered in water ice, the tiny (barely more than 300 miles in diameter) moon reflects almost 100% of the sunlight which strikes it. Because of this, Enceladus’ surface temperature is an extremely frigid -201° C (-330° F). Until fairly recently the icy satellite was thought to be cold and dead. (Image Credit: NASA)

In 2005 NASA’s Cassini Spacecraft discovered water vapor and ice spewing from vents near Enceladus’ south pole. Researchers at the time theorized the presence of an interior reservoir of water and subsequent observations of the jets showed them to be relatively warm, compared with other regions of the moon, and to be salty. All solid arguments for there being liquid water below the surface, and with this the possibility of extraterrestrial microbial  life.

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Taken by Cassini in November 2009 as the spacecraft flew past Enceladus and through the jets, the above image shows dramatic plumes, both large and small, spraying icy particles from many locations along the south pole of the moon. More than 30 individual jets of different sizes can be seen. (Image Credit: NASA/JPL/Space Science Institute)

On yesterday, April 3, 2014, researchers at NASA’s Jet Propulsion Laboratory (JPL) announced that new data gathered from Cassini and NASA’s Deep Space Network providing the first geophysical measurements of the internal structure of Enceladus is consistent with the existence of a hidden ocean inside the moon. The new findings from the gravity measurements are published in today’s (Friday, April 4) edition of the journal Science.

“The way we deduce gravity variations is a concept in physics called the Doppler Effect, the same principle used with a speed-measuring radar gun,” Sami Asmar of JPL, a coauthor of the paper in Science, said in a news release from JPL“As the spacecraft flies by Enceladus, its velocity is perturbed by an amount that depends on variations in the gravity field that we’re trying to measure. We see the change in velocity as a change in radio frequency, received at our ground stations here all the way across the solar system.”

Cassini has flown near Enceladus 19 times. Precise trajectory measurements were made during three flybys, from 2010 to 2012. The gravitational tug of a planetary body alters a spacecraft’s flight path, and variations in the gravity field, such as those caused by mountains or differences in underground composition, can be detected as changes in the spacecraft’s velocity. The technique of analyzing a radio signal between Cassini and the Deep Space Network can detect changes in velocity as small as less than one foot per hour, or 90 microns per second. With this precision, the flyby data yielded evidence of a zone inside the southern end Enceladus with higher density than other portions of the interior.

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Inside Enceladus: Illustration depicting jets of water vapor and ice gushing from Enceladus’ south pole and a large interior ocean beneath an ice shell. (Image credit: NASA/JPL-Caltech)

“The Cassini gravity measurements show a negative gravity anomaly at the south pole that however is not as large as expected from the deep depression detected by the onboard camera,” the paper’s lead author, Luciano Iess of Sapienza University of Rome, said in the JPL news release. “Hence the conclusion that there must be a denser material at depth that compensates the missing mass: very likely liquid water, which is seven percent denser than ice. The magnitude of the anomaly gave us the size of the water reservoir.”

The gravity measurements suggest a large, possibly regional, ocean about 6 miles deep covered by an ice shell about 19 to 25 miles thick. It’s not known for certain whether the subsurface ocean supplies the water plumes near the moon’s south pole, however scientists think it’s a real possibility. The fractures may lead down to a part of the moon that is tidally heated by the moon’s repeated flexing as it follows its eccentric orbit around Saturn.

Before Cassini reached Saturn in July 2004 there was no short-list which included this small icy world among the most likely places in our solar system to host microbial life. That’s changed. What else do we not know, and won’t know until we go? And what else can we, as a species, decide is a more important endeavor in which to spend a small fraction of our time and resources in discovering.  If you agree, The Planetary Society is hosting a petition to reject the White House’s cut to Planetary Science at NASA. Signing up is quick and easy. And for non-US citizens, there’s also a form to email President Obama asking that he rejects the cuts and works towards keeping scientific research alive for the future of all humanity.

33 responses

  1. They can measure that it’s 19 to 25 miles of ice?
    That’s some impressive math and science!

    April 4, 2014 at 7:27 am

    • I never fail to be impressed Guapo! I don’t have the kind of mind that can easily wrap itself around such calculations, but wow, am I ever impressed by those who do!

      April 4, 2014 at 7:36 am

  2. Isn’t it amazing (and depressing)… the money the IMF just channeled to keep the Ukraine afloat (meaning, paying its bills to the world’s banks) would pay for a serious mission to this moon. Arghhhh!

    April 4, 2014 at 7:28 am

  3. Underground sea? I’ll go grab my fishing rod and…oh wait: It is on Enceladus!

    (Stay tuned for Cassini’s next dozen orbits; it’s sure to discover the mating call of Saturian mermaids!)

    April 4, 2014 at 8:06 am

    • Saturian mermaids?!! Didn’t I see that on an old Star Trek episode? If Cassini does pick up on some mermaid and/or siren call, future missions are then sure to be funded. Mermaids ALWAYS get funding….

      April 4, 2014 at 8:22 am

  4. This isn’t the first moon to be seen shooting jest of water out. I cannot remember what the others are, but I’m sure you do. I assume that this moon doesn’t have an atmosphere, and therefore it must be losing this water into space, no? It just seems intuitive that the water should run out… at some point… over these millions of years. Even though I guess there’s a lot. I suppose as the moon orbits then the vapour could come into contact with it and re-freeze. I don’ know.

    And talking of funding I found out today from a radio documentary about the human effort to fend off the destruction of all life on earth from asteroid impact. In Britain David Cameron cut their funding the National Near Earth Information Centre and it’s now funded solely by selling key rings in the shop… Sleep tight everyone. Best not to think about it, eh?

    April 4, 2014 at 8:24 am

    • Jupiter’s moon, Europa, has water vapor plumes, but I remember you and I having a similar exchange about the water vapor found venting on dwarf planet Ceres a few months ago. In the case of Ceres, the best explanation I could find as for why the water doesn’t run out is because of sublimation. Enceladus does have an atmosphere, composed primarily of water vapor, and it’s a significant atmosphere compared to Saturn’s other moons – I mean other than Titan, of course. From what I’ve read, some of the material from Enceladus’ water jets does fall back onto it’s surface (sort of like snow), some of it reaches Saturn, and the E ring is thought to be made up entirely of Enceladus ice particles.

      About potential asteroid impacts and our failure to address it, it definitely is one of my ‘don’t get me started’ topics. I’m sure you’ve heard that old joke about the dinosaurs becoming extinct because they lacked a space program, we don’t have such a good excuse. I’m amazed at how short-sighted we can be. Now, how can I get me one of those key rings….

      April 4, 2014 at 9:48 am

      • Yeah I imagined I’d been banging on about it before. Still, snow in space would be nice. It seems odd that, with such low temperatures, that the whole thing doesn’t just freeze over. Must (perhaps) be an odd thing to do with pressure (the pressure, temperature, and volume all being related, with gases at least) allowing the underground water to be liquid.

        Sadly, as far as I could find, they don’t even appear to have an on-line shop… We’re doomed. Or maybe just relying on America.

        April 5, 2014 at 4:56 am

        • Doomed? Or relying on America?

          Ok, I’m still laughing….. :D

          April 5, 2014 at 12:30 pm

          • Honestly we spend billions – that we don’t have – on nuclear weapons and the like when there’s no point. They’re completely useless. We should be boxing clever, scrapping them and spending the money on libraries and nurses and scientific research, and just relying on the threat of your arsenal with any worldwide hissy fit as it’s not likely we’re going to be on different sides in the near future.

            April 5, 2014 at 12:41 pm

  5. I was out of town for the past 5 days. I noticed a news item yesterday that briefly mentioned this story. But, I had no time to look into it. Thanks for getting the details out in this clear and easy to follow post. This is great news.

    I will head for those petitions next.

    Thanks, Alex.

    April 4, 2014 at 11:49 am

    • Easy to follow is the only way I know, Jim ;)

      And THANKS for signing the petition, I kinda thought you would!

      April 5, 2014 at 12:22 pm

  6. Governments…(wanders off grumbling)

    April 4, 2014 at 2:56 pm

    • Did I notice some head shaking going on along with that grumbling, Richard? ;)

      April 5, 2014 at 12:24 pm

  7. whiteladyinthehood

    Remarkable!!

    April 5, 2014 at 8:22 am

    • Indeed, Chica!

      And, I hope you’ve been well!

      April 5, 2014 at 12:23 pm

  8. Very exciting news… Enceladus fascinates me – for one thing it even looks a lot like Europa – as though they were twins separated at birth. For another, the moon looks pretty organic in a lot of photos – especially with the blue “tiger stripes” looking like blood veins. Makes me think of the egg from Alien! Maybe Enceladus is actually LV-426… hmm… if I recall, that world orbiting a planet with rings too…

    …*cue Twilight Zone music*

    April 5, 2014 at 11:36 am

    • Ok, Richard, you’ve just completely creeped me out – but not in a totally uncool way ;)

      I’ll never look at Enceladus’ “tiger stripes” quite the same again.

      April 5, 2014 at 12:27 pm

  9. Well first of all, I can’t go to Enceladus. If the atmosphere is mainly water vapor, I’d definitely come down with a horrific sinus infection.. Secondly, maybe Enceladus is experiencing some kind of internal global warming and the hidden reservoir once was a solid…but it’s now melting and that’s why jets of water are shooting out of it…I just hope it doesn’t shoot a polar bear out of one of it’s jets..that would just be cruel.

    OH! And the asteroids…I just found out yesterday, that supposedly FIFTEEN years ago, drones the size of mosquitos existed…..
    So I’ve got to go now….I have to get my squirt gun ready, so that I can shoot down an asteroid if I have to…and then I have to get some special spy glasses so that I can detect teeny tiny drones and smack them with a giant fly-swatter…and then I have to dig a hole in the ground that I can crawl into, to get away from all of the drones that I CAN’T see and the polar bars falling out of the sky at the end of their journey from Enceladus.
    I’m gonna need a LOT of chocolate.

    April 6, 2014 at 3:55 pm

    • LOL!!!!

      Well, I can honestly say I feel A LOT better knowing you now have the asteroid problem taken care of. I don’t know why no one has thought of this solution before now. I like your ‘out of the box’ thinking ( and I do mean WAAAAYYYY out of the box!). And yep, this will require lots of chocolate. Maybe polar bear shaped chocolate….
      ;)

      April 8, 2014 at 6:37 am

      • Gadzooks! Polar bear shaped chocolate!!
        My apologies for so much silliness on such serious subjects.
        I do find Enceladus fascinating….and the subject of ignoring asteroid defense….well….I’m afraid some of the dinosaurs that experienced an asteroid up close and personal had a LOT more brains than some of our decision makers…If that’s not scary, I don’t know what is.

        April 9, 2014 at 8:35 am

        • NEVER apologize for silliness, especially on serious subjects! It helps divert attention from the fact that we could easily go the way of the dinosaurs. Silliness and chocolate will pull us through! We REALLY can’t count on our decision-makers.

          April 9, 2014 at 9:22 am

          • SCARY…..

            April 9, 2014 at 9:24 am

            • Quick dear, find your Happy Place – picture a warm beach, crystal blue waters, trade winds, a hammock perfectly placed between two coconut palms, a drink containing dark rum and an tiny umbrella, and a beach-volleyball player named ‘Raul’ feeding you starfish shaped chocolates….

              April 9, 2014 at 9:39 am

              • Ooooooohh “Raul”!…..

                April 9, 2014 at 2:47 pm

                • Oh yeah, Raul…. ;)

                  April 12, 2014 at 7:23 am

                  • I imagine that Raul smells like coconut…don’t ask me why.

                    April 13, 2014 at 6:46 am

              • LOVE THE VIDEO!!!!!!

                April 9, 2014 at 2:47 pm

  10. A natural setting for a perpetual ice hotel! Well done, Alex …. all new to me.

    April 6, 2014 at 6:57 pm

    • HA! Good morning Frank :) I remember the ice hotel, and you’re right – Enceladus would definitely be the perfect place for it. Just remember to make your reservations really far in advance!

      April 8, 2014 at 6:38 am

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