Aside from Earth, Titan is the only place in the solar system that has bodies of liquid on its surface, making it a rather attractive place to explore. But while a number of proposals have been put forward to take a closer look, none have come to fruition.

Step forward the Titan Submarine, a proposal that NASA has just awarded a second round of funding through their Innovative Advanced Concepts (NIAC) program. It is very much just a concept at the moment, but it is promising nonetheless.

Somewhat similar to an Earth-based submarine, the cylindrical vessel about the length of a car would plunge through the thick atmosphere of Titan and dive into its largest liquid hydrocarbon sea, Kraken Mare. Here, it would explore the subsurface region for 90 days, sending data and images back to Earth. It would travel at a rather sedate one meter (3.3 feet) per second using four propellers at its back, enabling it to cover a planned route of 2,000 kilometers (1,200 miles). Instruments on board would include sonar, a sampling system and a camera to answer questions such as whether there could be life on Titan, which is up for debate.

The team, led by Steven Oleson of NASA’s Glenn Research Center in Ohio, envisages that the vehicle could splashdown in 2040. There are a number of complications to overcome before the idea can even be considered for development though. These include "basic physics questions" of operating in the -180°C (-300°F) liquid seas of Titan, and working out how to actually launch the submarine to Titan.

"Risks of an exposed phased-array antenna to communicate directly back to Earth will also be explored," the scientists note in their proposal, referring to the difficulties of the submarine having its own communication system on board. Instead, it may have a simpler device that talks to an orbiter, with data relayed to Earth, much like the Huygens lander did with Cassini in 2005, the first and only landing on Titan so far.

Shown is sunlight glinting off seas on Titan, as seen by the Cassini spacecraft via NASA / JPL-Caltech / University of Arizona / University of Idaho

The goal of the NIAC program is to start funding for ambitious proposals like this. The Titan Submarine will be awarded up to $500,000 (£325,000) over two years, and six other concepts have also been awarded funding. They include SCEPS (Stored Chemical Energy Power Systems) in Space, a way to power deep space probes for long periods of time with lithium rather than plutonium. One team has proposed reflecting sunlight into the bottom of craters on the moon, enabling a rover to study these potentially ice-rich regions, while another concept would use a swarm of "small, low-cost probes" to calculate the gravity and mass of asteroids and comets.

“NASA's investments in early-stage research are important for advancing new systems concepts and developing requirements for technologies to enable future space exploration missions," said Steve Jurczyk, associate administrator for the Space Technology Mission Directorate at NASA Headquarters in Washington, in a statement.

"This round of Phase II selections demonstrates the agency's continued commitment to innovations that may transform our nation's space, technology and science capabilities."