Dream of sailing on Titan’s lakes

A robotic rover has crawled across the Martian surface and a probe has been smashed into a comet at supersonic speed.

Now Nasa scientists are proposing another interplanetary first – sailing a boat on the methane lakes of Titan, Saturn’s largest moon.

Ellen Stofan, Nasa’s chief scientist, proposed the Titan Mare Explorer (TiME) mission before her appointment and said she was ‘‘hopeful’’ that the plan to sail a boat on Titan’s lakes of liquid methane would be realised.

Titan’s icy surface is broken up by rivers and lakes, giving it an eerie similarity to Earth. – ‘‘like the North Sea on a cloudy day, but considerably colder’’, Stofan said.

Rather than water, the lakes are filled with a mixture of methane and ethane, which are gases on Earth but liquid on the surface of Titan, which has a temperature of -180 degrees Celsius. The TiME mission would involve parachuting a boat into a lake in Titan’s northern hemisphere.

Powered by heat from an onboard plutonium supply, the probe would bob around the lake’s surface and take measurements for about three months.

Ralph Lorenz, of Johns Hopkins University in Maryland, who has taken over as principle investigator of the TiME project, said: ‘‘It is essentially a drifting buoy much like those used in terrestrial oceanography. The dominant movement is due to the wind so you can think of it as sailing.’’

The probe would sample the chemistry of the lake, which some scientists have speculated could host microscopic life forms, even in the absence of liquid water.

‘‘There’s a huge question of whether you really need water for life,’’ Stofan said.

Nasa is soliciting mission proposals for launch about 2021, but TiME may have to wait longer as scientists are working to develop the necessary power source for the boat.

‘‘Realistically a mission like this now needs to wait until about 2040,’’ Lorenz said.

Stofan said there was also excitement building about a first manned Mars mission, which Nasa is aiming to launch by the 2030s. On any Mars mission, she said, the two major hurdles would be shielding the astronauts from powerful radiation and bringing a sizeable spacecraft to a soft landing fast enough – an experience that she predicts will be ‘‘seven and a half minutes of terror’’ for all involved.

Interplanetary first: An illustration of the Titan Mare Explorer afloat on a lake of liquid methane on Saturn’s moon, Titan.

Photo: REUTERS The target: Titan, Saturn’s largest moon appears before the planet as it undergoes seasonal changes in this natural colour view from Nasa’s Cassini spacecraft.