posted June 21, 2008 01:15 PM         

Chunks of bright material unearthed by NASA's Phoenix Mars Lander have vanished again after around four days. Scientists say this is the "smoking gun" that convinces them they've found water ice, which vaporised when exposed to the Martian atmosphere. Watch an animated gif of the ice vaporising.

"It must be ice," says Phoenix lead scientist Peter Smith of the University of Arizona in Tucson, US. "These little clumps completely disappearing over the course of a few days – that is perfect evidence."

The Phoenix lander uncovered the bright material when its robotic arm was widening a trench, informally called "Dodo-Goldilocks", on 15 June. A camera called the Surface Stereo Imager revealed bright chunks roughly a couple of centimetres wide at the trench's base.

Vanishing chunks
One possibility was that the chunks were some kind of salt. But four days later, new images revealed that some of the chunks had vanished. "Salt can't do that," says Smith.

The Phoenix team concludes that the bright material must be water ice that vaporised when exposed to the Martian atmosphere, a process called sublimation.

The lander's robotic arm has also hit a hard surface that might be dense ice while digging another trench, dubbed "Snow White 2". The arm went into a holding position after three attempts to dig through the hard material – the expected action when the arm hits something that's challengingly hard.

Hard layer
Like the bright chunks, the hard layer is about 5 or 6 centimetres under the surface. "We have dug a trench and uncovered a hard layer at the same depth as the ice layer in our other trench," says team member
Ray Arvidson of Washington University in St Louis, Missouri, US.

Phoenix mission scientists are delighted that the lander has touched water ice, because the spacecraft's main goal is to find out the history of water on Mars and assess whether the planet has ever been hospitable to life. NASA plans to release more details of the new findings at a press conference later today.

posted June 21, 2008 04:40 PM         

YES!!!!