Cassini radar images of possible lakes at Titan's north pole. The dark patches in each image are thought to be the lakes and liquid may run into them along the channel features. The two views are roughly 450 km by 150 km. Image: NASA / JPL The Cassini spacecraft, a joint project between NASA and the European Space Agency (ESA) has discovered lakes on Saturn’s moon Titan.

Titan is the only moon in the solar system with a significant atmosphere, made up almost exclusively from nitrogen with a small amount of methane and traces of other gases. The satellite is in deep freeze with a surface temperature of -180° C (or 94 K), but astronomers have long been interested in the chemistry on its surface with many compounds thought to be similar to those found on the primordial Earth.

Artist's impression of the Huygens lander descending through the Titanian atmosphere. © ESA In January 2005 the ESA probe Huygens made the first landing on Titan, sending back images of a landscape with channels and other features that appeared to have been carved by liquid. But later results suggested many of the dark smooth areas that resembled lakes and seas in radar images were really made from a sand-like material.

The new Cassini images show areas near the Titanian north pole that are completely black and reflect no radar signal, which implies they are extremely smooth and may contain liquid. Rims around these ‘lakes’ may be where material is deposited as the liquid evaporates.

Like the Earth, Titan experiences seasons as it changes its orientation to the Sun. Cassini next flies past Titan in early September when the search for liquid will continue. Scientists are intrigued to see whether the lakes change shape as spring comes to the northern hemisphere of this frigid moon.