An ocean lies a few kilometers beneath Enceladus's icy surface

An ocean lies a few kilometers beneath Enceladus's icy surface
Image showing the thickness of Enceladus's ice shell, which reaches 35 kilometers in the cratered equatorial regions (shown in yellow) and less than 5 kilometers in the active south polar region (shown in blue). Credit: LPG-CNRS-U. Nantes/U. Charles, Prague.

With eruptions of ice and water vapor, and an ocean covered by an ice shell, Saturn's moon Enceladus is one of the most fascinating in the Solar System, especially as interpretations of data provided by the Cassini spacecraft have been contradictory until now. An international team including researchers from the Laboratoire de Planétologie Géodynamique de Nantes (CNRS/Université de Nantes/Université d'Angers), Charles University in Prague, and the Royal Observatory of Belgium recently proposed a new model that reconciles different data sets and shows that the ice shell at Enceladus's south pole may be only a few kilometers thick. This suggests that there is a strong heat source in the interior of Enceladus, an additional factor supporting the possible emergence of life in its ocean. The study has just been published online on the website of Geophysical Research Letters.

Initial interpretations of data from Cassini flybys of Enceladus estimated that the thickness of its ice shell ranged from 30 to 40 km at the south pole to 60 km at the equator. These models were unable to settle the question of whether or not its extended beneath the entire ice shell. However, the discovery in 2015 of an oscillation in Enceladus's rotation known as a libration, which is linked to tidal effects, suggests that it has a global ocean and a much thinner ice shell than predicted, with a mean thickness of around 20 km. Nonetheless, this thickness appeared to be inconsistent with other gravity and topography data.

In order to reconcile the different constraints, the researchers propose a in which the top two hundred meters of the ice shell acts like an elastic shell. According to this study, Enceladus is made up successively of a rocky core with a radius of 185 km, and an internal ocean approximately 45 km deep, isolated from the surface by an ice shell with a mean thickness of around 20 km, except at the south pole where it is thought to be less than 5 km thick. In this model, the ocean beneath the ice makes up 40% of the total volume of the moon, while its salt content is estimated to be similar to that of Earth's oceans.

All this implies a new energy budget for Enceladus. Since a thinner ice shell retains less heat, the tidal effects caused by Saturn on the large fractures in the ice at the south pole are no longer enough to explain the strong heat flow affecting this region. The model therefore reinforces the idea that there is strong heat production in Enceladus's deep interior that may power the hydrothermal vents on the ocean floor. Since complex organic molecules, whose precise composition remains unknown, have been detected in Enceladus's jets, these conditions appear to be favorable to the emergence of life. The relative thinness of the ice shell at the could also allow a future space exploration mission to gather data, in particular using radar, which would be far more reliable and easy to obtain than with the 40 km thick initially calculated. It looks as if Enceladus still has many secrets in store.


Explore further

Image: Enceladus and Saturn's rings

More information: Ondřej Čadek et al. Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape and libration data, Geophysical Research Letters (2016). DOI: 10.1002/2016GL068634
Journal information: Geophysical Research Letters

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Citation: An ocean lies a few kilometers beneath Enceladus's icy surface (2016, June 22) retrieved 19 August 2019 from https://phys.org/news/2016-06-ocean-lies-kilometers-beneath-enceladus.html
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Jun 22, 2016
It would really help to wait until we land a probe on its surface to take accurate seismic readings as that would settle and pin down once and for all with certainty both the exact thickness of the ice and the exact diameter of the rocky core thus take out much of the unwelcome guesswork out of the models.

Jun 22, 2016
From ice shell to water veil to exposed surface of rock.

Jun 22, 2016
45 km deep. That might be an issue if we want to send something like cryobot to explore in Enceladus. Any hydrothermal vents would be that deep down. Bridging a 45km gap to the surface for data transmission is going to be tricky.

Jun 22, 2016
Changes:
- Thinner ice at the jets.
- Larger ocean.
- The salt content is modified towards that of our own oceans:
- The heat flow is increased and chooses the hydrothermal vent model as the remaining viable: "... the tidal effects caused by Saturn on the large fractures in the ice at the south pole are no longer enough to explain the strong heat flow affecting this region."

In short, Enceladus becomes a more interesting target for astrobiology exploration.

@humy, aap: The ELF (Enceladus Life Explorer) mission will dive through the jets and characterize their organics and eventual cells. It will also have a magnetometer IIRC, which would characterize the ocean and the ice.

Re later missions into the oceans, I assume they could use automatic return to the release station/drill, which would house a nuclear energy source and relay findings to a surface craft. That has been suggested for Europa. It means "just" 5 km of optic fiber....

Jun 22, 2016
This comment has been removed by a moderator.

Jun 22, 2016
Which hypothesis? That Enceladus has an ocean? Its large physical libration has ruled out rigid models by more than 10σ (10 sigma). http://www.scienc...15003899 It definitely has an ocean.

If you want to consider a heavily marketed hypothesis that makes unwarranted claims, look no further than EU acolytes that proclaim the southern jets are the result of electric discharge machining and yet offer no reason why only the south pole is targeted, year after year after year.

Jun 22, 2016
Why do you imagine that libration can differentiate the two models? EM has been claimed to affect planetary rotation since the time of Velikovsky.

"During the August 11, 2008 flyby, Cassini's plasma sensors found ion and electron beams propagating from Saturn's northern hemisphere. Their variability was something of a puzzle until it was noted that time-variable emissions from Enceladus' south polar vents could correspond with the footprint's brightness variations in Saturn's aurora."

(https://www.thund...be-dgm/)

Jun 23, 2016
Why do you imagine that libration can differentiate the two models? EM has been claimed to affect planetary rotation since the time of Velikovsky.

"During the August 11, 2008 flyby, Cassini's plasma sensors found ion and electron beams propagating from Saturn's northern hemisphere. Their variability was something of a puzzle until it was noted that time-variable emissions from Enceladus' south polar vents could correspond with the footprint's brightness variations in Saturn's aurora."

(https://www.thund...be-dgm/)


Which would be very interesting were it not for the fact that we already know that the jets are composed of H2O. It's a bit like your electric comet nonsense; yesterday's (i.e. shown to be wrong decades ago) news. At least try to keep up. They flew through these plumes recently.

Jun 23, 2016
Which would be very interesting were it not for the fact that we already know that the jets are composed of H2O. It's a bit like your electric comet nonsense; yesterday's (i.e. shown to be wrong decades ago) news. At least try to keep up. They flew through these plumes recently.


You seem to believe that precludes any suggestion of EDM causing the plumes, which we know has origins in your complete ignorance. You do know electrochemical reactions occurs in plasmas, correct? Oh right, you didn't know this, I think your comment was "where's the electrolyte?". Speaking of keeping up, you can start by removing your head from your ass.

Jun 23, 2016
It would really help to wait until we land a probe on its surface to take accurate seismic readings as that would settle and pin down once and for all with certainty both the exact thickness of the ice and the exact diameter of the rocky core thus take out much of the unwelcome guesswork out of the models.

By using the models as a guide, they could take out much of the unwelcome guesswork out of the instruments they send on a probe.

Jun 23, 2016
Why do you imagine that libration can differentiate the two models? EM has been claimed to affect planetary rotation since the time of Velikovsky. -ChrisAlfven
Many claims have been made, including that Santa Claus is real. Velikovsky was a physician, not a physicist, and the poor quality of his claims reflects that.

Jun 23, 2016
https://www.thund...be-dgm/
@ha
phishing pseudoscience site
source material would be far better than a pseudoscience site
the fact that you can't find source material is telling and indicates reptilian reactionary posting sans logic or forethought

.

that precludes any suggestion of EDM
@cd
there is no evidence to support the EDM and there are far better explanations with more evidence to support them, with a far better probability of occurrence than EDM

this is similar to your whole "moon craters" argument:
it's not "that" we think none are from EDM, it's that the probability of EDM drops to nil when we can see strikes, measure them, predict them, validate them, and have evidence for them while not having evidence at all whatsoever for EDM

.

i will leave you with your own words quoted verbatim back at ya -

"Speaking of keeping up, you can start by removing your head from your ass."

Jun 23, 2016


i will leave you with your own words quoted verbatim back at ya -

"Speaking of keeping up, you can start by removing your head from your ass."


Mate, do you seriously think these eejits are ever going to come up with something believable?
Not going to happen. Which is why we have to put up with the likes of CD and others, trolling this site with their scientifically illiterate nonsense. If they had anything to say, they'd have said it by now. Seriously, it will not happen.

Jun 24, 2016
Not going to happen. Which is why we have to put up with the likes of CD and others, trolling this site with their scientifically illiterate nonsense. If they had anything to say, they'd have said it by now. Seriously, it will not happen.

Just because you remain wilfully ignorant doesn't change the fact that they have indeed published papers.

And after billions upon billions of dollars and thousands of pseudoscientists looking they have yet to find DM. If they could find it they would have found it by now. Seriously, it will not happen....

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