The space agency says tests show the snow vaporized before reaching the red planet's surface.
Experiments by the probe also found evidence of past interaction between minerals and liquid waters.
The Phoenix confirmed the presence of water-ice after landing on Mars on May 25.
NASA scientists want to determine if the ice ever thaws, creating conditions favorable for life.
The Phoenix mission was originally planned for three months but is now in its fifth month. However, NASA says the probe's solar energy is diminishing, likely ending its ability to work by the end of the year.
Reported by VOA News.
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