The Huygens probe, part of a $3 billion joint mission involving Nasa and the European and Italian space agencies, made its pioneering descent to Titan on Friday, sending back readings on the moon's atmosphere, composition and landscape.

Slowed by parachutes, Huygens took more than two hours to float to the icy surface, where it defied expectations of a quick death and continued to transmit for at least two hours.

Along with scientific instruments that measure the components of Titan's atmosphere, Huygens carried a sound recorder and lamp to look for signs of surface liquid.

Data

One reading from an instrument protruding from the front of the saucer-shaped craft to gauge how deeply it penetrated upon impact suggested that the moon's surface was the consistency of wet sand or clay.

"We think this is material which may have a thin crust, followed by a region of relatively uniform consistency," John Zarnecki, the scientist in charge of experiments on Titan's surface, said.

Titan, believed to be the only moon in the solar system with an atmosphere, is larger than the planet Mercury. Scientists believe a study of the icy moon could yield clues about how life developed on Earth.

A panoramic picture sent back from Huygens shows what appears to be a coastal area with banks of fog-like clouds just above and a root-like system of rivulets just inland.

"It's almost impossible to resist the speculation that this is a drainage channel, that we are seeing a shoreline," said Martin Tomasko, a University of Arizona professor and the key researcher on images of the moon.

Other rock-sized objects photographed in an apparent flow channel on the gold-orange surface of Titan appear to be frozen blocks of water ice.