According to a NASA study, Saturn's moon Titan may be the most fantastically large slushie of all time. Based on a reexamination of data from the Cassini probe collected in 2012, the moon's long-suspected global ocean may actually be a slurry of ice and rock.
Many icy moons in the outer solar system are believed to harbor vast subsurface oceans sandwiched between thick ice shells and rocky cores. Since 2008, the methane-shrouded moon Titan has been thought to host such a global ocean beneath its frozen surface. However, a fresh look at the data sent back by the Cassini robotic orbiter and another go at the sums indicates that the truth might be less oceanic and more akin to a frosty dessert.
The case for Titan's ocean is based on more than just theoretical reasoning. By using the Deep Sky Network (DSN) tracking system, NASA was able to measure the Doppler shift of the radio signals from Cassini as it orbited Saturn and flew past Titan. These shifts allowed researchers to calculate how Titan’s gravity tugged on the spacecraft, revealing how flexible—or malleable—the moon is. In other words, they could determine how Saturn’s tidal forces distort Titan’s shape.
The original hypothesis was that Titan responded almost instantaneously to Saturn’s tides, deforming in near-perfect synchrony as it moved along its elliptical orbit. Since there was no time lag, the researchers argued that so fast a response had to be because the interior was liquid. This was backed up by estimates of the moon’s rigidity and by evidence that it retained enough internal heat to keep water liquid beneath its icy shell.
That changed when new, more sophisticated models were devised based on the same data. What the team discovered was that instead of being synchronized, there was a 15-hour lag in the tidal response. That didn't match either a watery or solid interior, but it did match one that was in a semi-solid or slushy state.
The new study shows that earlier estimates of the moon's rigidity had been misinterpreted and now better suit a mushy ice-rock mix. In addition, the new data suggests that Titan can transport enough heat away from the core to create a refreezing effect, separating the icy crust and the rocky core with a layer of slush with watery pockets.
According to the new model, Titan's "ocean" is really a slurry of ice slush made up of Ice VI and Ice VII, which are forms of ice that remain solid or semi-solid under immense pressure, and rock intermixed with pockets of warm water with a temperature of about 20 °C (68 °F). Such temperatures mean that, if minerals can migrate to these pockets, some primitive microbial life could theoretically exist.
"Nobody was expecting very strong energy dissipation inside Titan," said JPL postdoctoral researcher Flavio Petricca. "But by reducing the noise in the Doppler data, we could see these smaller wiggles emerge. That was the smoking gun that indicates Titan’s interior is different from what was inferred from previous analyses. The low viscosity of the slush still allows the moon to bulge and compress in response to Saturn’s tides, and to remove the heat that would otherwise melt the ice and form an ocean."
One point that hasn't been addressed is that, if the slushie hypothesis is correct, will future missions to Titan have to decide which flavored syrups to bring along?
The research was published in Nature.
Source: NASA
