they don't know where the water comes from, or what, besides salt, is in it >>> joining us is michael shura, curator of the department of the astro physics at the american museum of natural history in new york. good to have you hear with us. how confident are you that this is a done deal, and it's clear that some sort of water exists on mars? >> i don't think there's any doubt. there was strong evidence from the imaging that there was something that seemed to change. given the fact that there's the announcement of hydrochlorates, there's nothing more to argue about. there clearly has been, and recently, days, weeks, months, flowy briny water on mars. why with all the rovers, orbiters, including one from india that is there now, is it hard to determine with certainty, to prove beyond any kind of speculation, that the dark streaks are water? >> well, one of the problems is we don't have video coming back from mars, only still images, and you need to compare images taken days, weeks, months apart, and most of the time, 99.99% of the time you don't see changes, you have to look through huge amo