Because it is so far away from the sun, the average surface temperature is minus 290 degrees Fahrenheit. This fact means that water ice is as hard as rocks on Earth.
But, the cold temperature has also created a kind of weather cycle in which liquid methane and ethane substitute for water. Methane evaporates periodically, forms clouds in the largely nitrogen atmosphere, and eventually falls as rain.
The liquid methane with some ethane has formed hydrocarbon streams, lakes, and even seas on the surface of Titan, making it the only other world in the solar system besides Earth with stable oceans.
Most of what science knows about Titan has come from the Cassini probe (2) that has been orbiting Saturn for over the past ten years, flying periodically by the moons that make up the Saturn system.
When Cassini first arrived at Saturn it carried a smaller probe, the Huygens (2), which entered Titan’s atmosphere and touched down on its land surface, returning images and data for 90 minutes before going dark.
Follow-Up Mission to Saturn
With the great and still ongoing success of the Cassini mission, NASA scientists are already contemplating what kind of follow-up mission may be sent to the vicinity of Saturn. One of the more unusual concepts involves sending a drone submarine to Titan so that it can explore both the surface and the depths of the Kraken Sea, which resides near Titan’s North Pole.
The Kraken Sea measures 400,000 square kilometers and measures just 17 kilometers wide (3). It is thought to have a maximum depth of 160 meters. It has shallow waves, but also tides, currents, and possible whirlpools. The Kraken Sea was discovered by Cassini in 2007 and was named after the legendary sea monster in 2008.
NASA has previously looked at a boat to sail the seas of Titan, but now has decided on a submarine instead as the better option. The submarine, according to Gizmag, would weigh one metric ton (4).
The vehicle would use an electric propulsion system powered by a 1 kW radio thermal Stirling generator. It would use nitrogen for ballast when submerging and surfacing. The submarine would be able to travel about one meter per second. The mission would last about 90 days and would traverse 2,000 kilometers.
Prebiotic Materials in Kraken Sea
The great challenge would be delivering such an immense craft to Titan intact. It would likely be launched on a heavy-lift space launch system on a direct course to the Saturn system.
The submarine, because of its elongated shape, would enter the atmosphere of Titan inside a winged or lift body craft similar to the Air Force’s X-37. It would land on the Kraken Sea, and the delivery craft would sink to the bottom of the sea, leaving the submarine floating on the surface.
Building a submarine that could traverse the seas of Titan will be another great challenge. Liquid methane and ethane have different properties than does salt water, particularly in its density.
In any event, the submarine would perform an automatic checkout procedure before beginning its voyage in earnest. Every Earth day it will spend roughly eight hours submerged and 16 hours on the surface. While on the surface it will transmit its accumulated data to Earth before submerging once again.
NASA is particularly keen to find out what sort of prebiotic materials exist in the Kraken Sea, the better to discover clues as to how life may have begun on Earth. It will otherwise explore the composition and structure of the Kraken Sea from the surface to the sediment on the sea floor.
While on the surface, it will likely take what will be the iconic space image of the 21st century, of Saturn rising above the surface of Titan when there is a break in the clouds. In short, the voyage of the Titan submarine will be the most memorable one since humans first sailed the oceans of Earth.