Cassini Reveals Firm Evidence of a Very Salty Ocean Inside Saturn’s Largest Moon Titan

July 8, 2014

Space

Cassini Reveals Titan Has a Very Salty Ocean

Researchers found that Titan’s ice shell, which overlies a very salty ocean, varies in thickness around the moon, suggesting the crust is in the process of becoming rigid. Image Credit: NASA/JPL/SSI/Univ. of Arizona/G. Mitri/University of Nantes

New data from NASA’s Cassini spacecraft reveal that Saturn’s moon Titan has a very salt ocean, and support the idea that the moon’s icy shell is rigid and in the process of freezing solid.

Scientists analyzing data from NASA’s Cassini mission have firm evidence of an ocean inside Saturn’s largest moon, Titan, which might be as salty as the Earth’s Dead Sea. The findings are published in this week’s edition of the journal Icarus.

“This is an extremely salty ocean by Earth standards,” said the paper’s lead author, Giuseppe Mitri of the University of Nantes in France. “Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past.”

The new results come from a study of gravity and topography data collected during Cassini’s repeated flybys of Titan during the past 10 years. Researchers found that a relatively high density was required for Titan’s subsurface ocean in order to explain the gravity data. This indicates the ocean is probably an extremely salty brine of water mixed with dissolved salts likely composed of sulfur, sodium and potassium. The density indicated for this brine would give the ocean a salt content roughly equal to the saltiest bodies of water on Earth.

Their findings also support the idea that the moon’s icy shell is rigid and in the process of freezing solid.

The thickness of Titan’s ice crust appears to vary slightly from place to place. The researchers said this can best be explained if the moon’s outer shell is stiff, as would be the case if the ocean were slowly crystalizing, and turning to ice. Otherwise, the moon’s shape would tend to even itself out over time, like warm candle wax. This freezing process would have important implications for the habitability of Titan’s ocean, as it would limit the ability of materials to exchange between the surface and the ocean.

The data also touch on a major mystery: The presence of methane in Titan’s atmosphere. Scientists have long known that Titan’s atmosphere contains methane, ethane, acetylene and many other hydrocarbon compounds. But sunlight irreversibly destroys methane after tens of millions of years, so something has replenished methane in Titan’s thick air during the moon’s 4.5 billion-year history.

The rigid ice shell model published in Icarus suggests that any outgassing of methane into Titan’s atmosphere must happen at scattered “hot spots” (like the hot spot on Earth that gave rise to the Hawaiian Island chain), not from a broader process such as convection or plate tectonics.

“Titan continues to prove itself as an endlessly fascinating world,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, who was not involved in the study. “With our long-lived Cassini spacecraft, we’re unlocking new mysteries as fast as we solve old ones.”

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA’s Science Mission Directorate in Washington.

Publication: Giuseppe Mitri, et al., “Shape, topography, gravity anomalies and tidal deformation of Titan,” Icarus, Volume 236, 1 July 2014, Pages 169–177; DOI: 10.1016/j.icarus.2014.03.018

Source: Dr. Tony Phillips, Science@NASA

Image: NASA/JPL/SSI/Univ. of Arizona/G. Mitri/University of Nantes

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3 Responses to “Cassini Reveals Firm Evidence of a Very Salty Ocean Inside Saturn’s Largest Moon Titan”

  1. Conrad Winkelman Says:

    Is it not possible that Titan had a slightly denser core than it was calculated earlier, to account for a the higher gravity intensity, from which the conclusion was drawn that Titan’s sub-ice ocean has such a high salt content?
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    In regards to the assertion that Titan has a huge ocean under the ice and a solid core then there is a possibility . . .perhaps a certainty . . .that the solid core has and oscillatory motion with respects to the Ice Shell, assuming that the water at the high pressure that prevails there will be still have a rather low viscosity so that any varying radial motion of the core, relative to the ice shell, does not damp out.

    I am thinking in terms of differential tidal forces on the liquid water and the solid core from the Jupiter gravitation. The analogy is the tidal forces on the ocean water of the earth causing the surface of the water to be pulled towards the Moon and the Sun, causing the low and high tides, which essentially is relative radial motion between the ocean and earth surfaces and the iron core.

    In as far as the liquid iron “mantle” around the solid core is analogous to the “water” mantle around the solid core of Titan [which I assume there is] then the question I raise must also apply to the Earth it self, although liquid iron has presumably a much higher viscosity . . .I am shooting from the hip here as I hope this matter might be the field of study of one of the people reading this.

    I sort of envisioning that the solid core in a planetary size body of water might well meander about the geometric center of Titan at considerably large distances, especially if there are asymmetric forces tugging on the water and the core.

    Reply

  2. Conrad Winkelman Says:

    In my comments/questions above the “Jupiter gravitation” should of course be changed to “Saturn gravitation”.

    Reply

  3. Conrad Winkelman Says:

    After some extra background checking it may appears to be picture of Titan I had in mind at first is more like that of Jupiter’s Moon Europa with an Ice surface, which is not the case for Titan, but after all this it is clear the same question in regards to possibly the cores being within a liquid envelope having differential radial motion relative to the surface, applies of course to al similar cases.

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