How about playing Captain Nemo on Titan, Saturn’s largest moon, probing the depths of an ocean of methane and dodging oil icebergs over a billion miles from the sun? Some people think about it. To the point that one day perhaps, such a mission could see the light of day.
In some ways, Titan is the world that most resembles ours. Like the Earth, Saturn’s moon is enveloped in a thick atmosphere composed mainly of nitrogen. And like on Earth, it sometimes starts to rain. But on this world, when it rains, it rains gasoline. These hydrocarbons, mainly methane and liquid ethane (it is -180 ° C on the surface), sometimes congregate in rivers, carving canyons through mountains of frozen soot before flowing into lakes and seas.
Apart from the Earth, Titan is in fact the only body in the Solar System with stable liquids on the surface. You will find them mainly in areas north of the moon. The largest of these seas – Kraken Mare, named after a Nordic monster – is larger than all of the Great Lakes in North America combined.
Cassini spent thirteen years sailing the Saturnian system, mapping these features in detail.
On August 21, 2014, the probe passed approximately 900 km above the northern kingdoms of Titan. The researchers then took the opportunity to deploy its radar altimeter to measure the depths of Kraken Mare, as well as those of Moray Sinus, an estuary located on the north coast of the sea.
Roughly, the idea was to note the differences in radar return time between the liquid surface and the seabed. Its composition could also be estimated by highlighting the amount of radar energy absorbed during transit through the liquid. .
These works, initiated by Valerio Poggiali, of the Cornell Center for Astrophysics and Planetary Science, made it possible to estimate the depth of Moray Sinus: approximately 85 meters. According to the absorption of radar waves, this estuary would also be composed of 70% methane, 16% nitrogen and 14% ethane.
Analysis of elevation data in Kraken Mare, on the other hand, showed no evidence of returning signals from the seabed. In other words, the liquid is probably too deep for Cassini’s radio waves to reach the bottom. However, assuming that the composition of Kraken Mare is similar to that of Moray Sinus, the researchers estimated that its depth could reach 300 meters.
A submarine in Kraken Mare
For Valerio Poggiali, these works are much more than an abstract science. In the imagination of scientists, Titan indeed presents itself as a laboratory where, for millions of years, chemistry could have learned to generate energy and store information. “These are processes that also happened on our planet, but they left no trace!“, Notes the researcher. “So we must return to Titan to better understand the mystery of life“.
The best, to understand it, is still to go there. We have already “set foot” on Titan. In January 2005, ESA indeed succeeded in landing its Huygens lander on the surface after having taken measurements of its atmosphere during its descent.
We also know that NASA will be returning there as part of its Dragonfly mission. The idea: to release a small quadricopter capable of “leaping” into the atmosphere of the moon. Its launch is scheduled for 2027.
But like many other researchers, Dr Poggiali would also like to explore these famous hydrocarbon seas deeper, in the literal sense of the word.
With his team, they are currently imagining a mission to free a robotic submarine in the center of Kraken Mare. Here, the submersible would spend about three weeks measuring the composition of the seabed, before sailing close to shore, crossing the Bayta Fretum Strait and heading south through a gorge-shaped passage called the Seldon Fretum. From there it would go up to Moray Sinus.
With Titan’s surface gravity lower than Earth’s and methane less dense than water, a small submarine could venture deeper here without being crushed by the pressure. On 90 days of mission, such a machine could cover more than 3000 km under the sea.
If approved by NASA, Dr Poggiali points out that this ambitious mission could be launched in the 2030s to arrive there in the 2040s. At that time, he says, there will be more ambient light and the sub -marine could possibly communicate on a direct line to Earth without the need for a radio relay in orbit.