By Jonathan Amos
Science correspondent, BBC News, San Francisco
Ligeia Mare covers about 100,000 sq km in Titan's high north A daring proposal to try to put a "boat" down on a sea of Saturn's moon Titan is about to be submitted to Nasa. The scientific team behind the idea is targeting Ligeia Mare, a vast body of liquid methane sited in the high north of Saturn's largest moon. The concept will be suggested to the US space agency for one of its future mission opportunities that will test a novel power system. It would be the first exploration of a planetary sea beyond Earth. "It is something that would really capture the imagination," said Dr Ellen Stofan, from Proxemy Research, who leads the study team. Please turn on JavaScript. Media requires JavaScript to play. "The story of human exploration on Earth has been one of navigation and seafaring, and the idea that we could explore for the first time an extraterrestrial sea I think would be mind-blowing for most people," she told BBC News. Dr Stofan, who is also an honorary professor at University College London, has been describing her group's idea here at the American Geophysical Union's (AGU) Fall Meeting, the world's largest annual gathering of Earth scientists. Low cost The Cassini mission currently in orbit around Saturn has confirmed the haze-shrouded moon Titan to be an extraordinary place. Great lakes exist on its surface, fed by rivers that wash down valleys whenever it rains. TITAN MARE EXPLORER (TiME) A Nasa Discovery Class proposal, powered by ASRG technology Simple mission concept would hope to be low cost -
The historic image shows a telltale bright reflection

NASA have revealed that a flyby of its probe Cassini past Titan, a moon of Saturn, has produced a historic image: the first photograph showing liquid on a world other than our own.

The picture shows a "specular reflection" from an extremely smooth surface, in this case a liquid. Cassini has been trying to spot one since arriving in 2004, and in 2008 used infrared data to prove that there were liquid methane lakes down there. The northern hemisphere has only been visible since August 2009, as before then it was covered by winter weather. Most of Titan's lakes are in the north.

"This one image communicates so much about Titan — thick atmosphere, surface lakes and an otherworldliness. It’s an unsettling combination of strangeness yet similarity to Earth," said Bob Pappalardo, a Cassini scientist with NASA's Jet Propulsion Laboratory. Titan's atmosphere is, like Earth's, mainly nitrogen, but temperatures on the icy world are around -180°C. This reduces the prospect of life, although the presence of liquid does increase the likelihood.

The lake seen in the photograph is called Kraken Mare, and at 150,000 square miles (400,000 square kilometers), it isn't the largest basin on north Titan, but it is bigger than the Earth's biggest lake, the Caspian Sea.

Ralf Jaumann, another Cassini scientist, spoke of the team's hopes for the future. "Next, we want to find out more about Titan's liquid. Do we have some kind of weather there? Do we have changes with seasons? Does it rain? How does the liquid methane run across the surface?"

A team of scientists are due to propose to NASA that the agency drop a boat into a Titan lake, with Kraken Mare and the similarly sized Ligeia Mare being hot candidates. The Titan Mare Explorer (TiME) is projected to be relatively low-cost at US$400 million and would investigate the composition, density and shape of a Titan lake. If launched in 2016 it could arrive in 2023 and spend several years floating on the moon. However, several other projects are also keen to get themselves the next opportunity NASA is offering for the launch of a new project other than its own.