Many Mars flybys and probes have found evidence of water on planet Mars. Mariner 9 found water erosion and deposition, weather fronts and fogs. Viking 2 landed on Mars in its winter season and found frost. The Mars Global Surveyor, which could detect ancient water, found that Mars has been dry for a very long time. On December 6, 2006 NASA released photos of two craters called Terra Sirenum and Centauri Montes that showed liquid water at one point in 1999 and 2001. Pathfinder found that water existed before on Mars. Pathfinder confirmed that where it landed it is too cold for liquid water to be. However, water could be in its liquid state if it were mixed with various salts. Pathfinder also found evidence of clouds and maybe fog present in Mars. Mars Odyssey found much more evidence for water on Mars. The pictures taken by Odyssey confirmed that the ground is filled with ice. In July 2003, at a conference in California, it was said that the Gamma Ray Spectrometer (GRS) onboard the Mars Odyssey had found large amounts of water over large areas of Mars. Mars has enough ice just below the surface to fill Lake Michigan twice.