Scientists want to sail the seas of Saturn's moon Titan

Now that the Cassinimission to Saturn has come to an end, scientists are hoping to return, not just to the ringed planet itself, but to its moon Titan.And they want to explore it with balloons, boats and a submarine.

Titan is more like a planet than a moon. In fact, it is larger than the planet Mercury. It has a thick atmosphere made mostly of nitrogen, likeEarth. (You are breathing mostly nitrogen right now. Oxygen is only 20 per centof our air.)

• Farewell, Cassini: How a spacecraft helped us expand the search for life

And most interestingly, Titan is the only world in our solar system besides the Earth with lakes and rivers on its surface. The big difference is that the lakes are filled with liquid methane instead of water. The temperature on Titan is so low (-179C) that methane liquefies and goes through a similar cycle that water does on Earth, evaporating, forming clouds then raining back down into rivers and lakes.

This combination of air and liquid means that Titan can be explored with vehicles that could soar, sailor swim. Scientists have proposed a drone airplane that could circle the globe, a balloon that would drift on the gentle Titan winds,a sailboat, and even a submarine.

The aerial vehicles would cover far more terrain that the slow-moving rovers currently crawling around on Mars.They could even circumnavigatethe entire globe. A balloon could touch down from time to time in various locations to take soil samples.

The marine approach is far more interesting, something that has never been done on another world.Some of the lakes on Titan are very largeone of them is five times the size of Lake Superior, and estimated to be hundreds of metres deep, so it would an easy target for a splashdown.

Slow-motion waves

Methane is less dense than water, and the gravity on Titan is very low, similar to what the Apollo astronauts experienced on the moon. Waves would move in slow motion, making it easy for a powerboat or sailboat to get around.

A submarine is the most difficult concept because it would have to operate in a super cold liquid, then somehowbe able to communicate back to Earth. But it could provide the greatest return, exploring the depths of the lakes, searching for hydrothermal vents, and possibly even life.

It is that possibility of life that makes Titan such a compelling target for exploration. The carbon-based chemicals in its atmosphere and on the ground, such as methane, ethane, propane andoctane, are believed to be similar to those found on the early Earth before life emerged. One scientist described Titan as the primitive Earth in deep freeze.

Has primitive life evolved on Titan, or will it in the future, when the sun eventually turns into a red giant and the outer solar system warms up?

The chance that life emerged there, or that some kind of primordial soup exists on Titan means we have to be extremely careful with any spacecraft we send there. Care must be taken to ensure the vehicles are completely sterilized before leaving Earth so we don't contaminate the environment, or worse, create a "War of the Worlds" scenario where organisms from Earth wipe out those on Titan. And Saturn has another moon, Enceladus, which is believed to havea salty ocean beneath its icy surface that could also be a harbour for life.

Cross-contamination between worlds is a serious issue as we explore the solar system.

• NASA killed Cassini to avoid contaminating Saturn's moons

At the moment, there are no confirmed missions to return to the Saturn system, but based on the tremendous success of Cassiniand new mysteries it uncovered, the scientists are already at the drawing boards with visions of revisiting one of the most fascinating planets in the solar system.

• Bob McDonald:Cassini's grand finale: a death dive into Saturn
• A look back at stunning photos taken by NASA's Cassini spacecraft