"It must be ice," said Phoenix Principal Investigator Peter Smith of the University of Arizona, Tucson. "These little clumps completely disappearing over the course of a few days, that is perfect evidence that it's ice. There had been some question whether the bright material was salt. Salt can't do that."

The possible ice was found in a small trench, "Dodo-Goldilocks," which was made larger by a robotic arm on Phoenix.  

Working in a different trench nearby, Phoenix's arm found a hard surface that could be an icy layer, as scientists continue to try and determine if Mars could have been suitable for life.

Scientists have long debated amongst themselves as to whether or not the Red Planet of Mars had signs of liquid ice - one of the main goals of the Phoenix mission.  In 2002, the NASA Mars Odyssey was used to discover a permanent ice cap at the Martian north pole, with scientists believing a larger amount of ice is directly underneath the planet's surface.

NASA's next goal will be to try and collect samples of the water so instruments aboard Phoenix will be able to examine it.  A drill on the robotic arm could be used to break a small sample of the hard surface so it can be transferred to one of Phoenix's ovens.  

The discoveries come one day after Phoenix lost a day of productivity because of a glitch in which Phoenix's computer memory was full of the same image mistakenly copied repeatedly.  Engineers will send a patch over the weekend to make sure the same mistake does not happen again.

The Phoenix lander arrived on Mars on May 25 and is almost one month into a scheduled 90-day mission.