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

AP photo

This artist rendition provided by NASA and the Jet Propulsion Laboratory shows the Phoenix lander on the arctic plains of Mars.

Soil experiments revealed the presence of two minerals known to be formed in liquid water. Scientists identified the minerals as calcium carbonate, found in limestone and chalk, and sheet silicate.

But exactly how that happened remains a mystery.

“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 the 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.

Phoenix landed in the Martian arctic plains in May on a three-month mission to study whether the environment could be friendly to microbial life.

One of its biggest discoveries so far is confirming the presence of ice on the planet.