Prevailing theories suggest that Mars was once covered in a major liquid water system of rivers and lakes, which presupposes a thick atmosphere that can maintain temperatures at which liquid water can exist. But 3.5 billion years later, its barren

Coasting on Fumes A group of Silicon Valley guys are releasing potentially planet-cooling chemicals into the atmosphere — and are doing so from a nondescript Winnebago touring around Central California's coastline. As the New York Times reports,