Century-old fancies of a past Mars covered with warm, sparkling seas are fading, as scientists realize the planet’s rust-red surface has probably been a dry, frigid icebox for almost all of its history. That doesn’t necessarily mean that Martian microbes aren’t thriving at this very moment in volcanically heated subterranean swimming pools thousands of feet beneath the surface — the scientific jury is still out on that popular hypothesis. But whenever liquid water squirted to the surface during the past 3.5 billion years, it usually sloshed around for only brief periods before freezing or vaporizing in the drier-than-Sahara wasteland, judging by scientific evidence reported Monday at the annual San Francisco meeting of the American Geophysical Union.