Nobody knows what life forms may exist outside our own planet. The search for extra-terrestrial life in the universe took a step nearer to fruition with the discovery in June of what are believed to be traces of water on the surface of Mars. Life on our planet requires water and its presence on Mars may point towards the existence of past life on the planet. The Phoenix Mars Lander robot landed on the plains of Mars on May 25th 2008, searching for signs that the Martian environment might once have been habitable to life. When it dug a ditch in the planets surface, photos revealed small patches of bright material. Four days later those patches had disappeared, causing scientists to speculate that they were water ice that had previously been buried and which vaporised when exposed to the air. Scientists insisted that if the patches had been salt, they wouldn't have disappeared and if they had been solid carbon dioxide, then they wouldn't have vaporised.

Question: The Phoenix Mars Lander has provided proof that life once existed on Mars.
Options:
A. true, B. false, C. uncertain
Answer: "C"