Phoenix spent five months on the surface of Mars. It was in the polar region of Mars, trying to give us a better idea of the geology and climate. One of the papers published in Science shows evidence of snow on Mars. Peter Smith, the Phoenix Principal investigator, said, "Frost was predicted, but snowfall was quite a welcome surprise."
These scientists found that the water was freezing out of the clouds at night and then sublimating (turning from ice to vapor without turning to a liquid) in the morning. This discovery was made with the LIDAR on Phoenix. The LIDAR sends a laser burst straight up, and observes how the light scatters of dust and ice. The researchers also found water clouds that were imaged by Phoenix. This is incredibly exciting. Phoenix may have died nine months ago, but the discoveries keep pouring out.
Source- Universe Today