LOS ANGELES – NASA's Phoenix spacecraft has discovered evidence of past water at its Martian landing site and spotted falling snow in the sky for the first time, scientists reported Monday.

Soil experiments reveal the presence of minerals known to be formed in liquid water, but exactly how that happened remains a mystery. Scientists think there could have been standing water at the site in the past or the ice could have melted and interacted with the minerals.

“It's really kind of all up in the air,” said William Boynton, a mission scientist at the University of Arizona at Tucson.

A laser aboard Phoenix recently detected snow falling from clouds more than two miles above its home in the northern arctic plains. The snow disappeared before reaching the ground.

Since arriving in May, Phoenix has been busy digging trenches with its long robotic arm, and delivering scoopfuls of dirt and ice to its instruments to study whether the environment could be friendly to microbial life.

One of its biggest discoveries so far is confirming the presence of ice. Scientists long suspected there was frozen water buried in the northern plains based on measurements from an orbiting spacecraft. The lander also found that the soil was slightly alkaline and contained important nutrients and minerals.

Scientists identified the minerals as calcium carbonate, found in limestone and chalk, and sheet silicate. On Earth, these types of minerals normally form in liquid water.

“Is this a habitable zone on Mars? I think we're approaching that hypothesis,” said chief scientist Peter Smith of the University of Arizona. “We understand, though, that Mars has many surprises for us and we have not finished our investigation.”

Mars today is frigid and dry with no sign of water on the surface, but researchers believe the planet once was warmer and wetter.

Originally scheduled as a three-month mission, NASA has extended operations through the end of the year if Phoenix can survive that long. With summer waning, less power is reaching the three-legged spacecraft's solar panels that convert sunlight into electricity.

Phoenix will be out of touch with ground controllers briefly in November when the sun is between Earth and Mars, blocking communications.

Scientists are racing against time to use up the remaining four of Phoenix's eight tiny test ovens before the lander dies. The ovens are designed to sniff for traces of organic, or carbon-based compounds, that are considered the building blocks of life. Experiments so far has failed to turn up definitive evidence of organics.

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