Recent discoveries spark space race between Europeans and Americans to find another Earth The announcement by American astronomers last week that they had discovered the two smallest planets yet orbiting nearby stars, trumped a small planet discovery by European scientists five days earlier and capped the latest round in a frenzied hunt for other worlds like Earth. All three of these smaller planets belong to a new class of ''exoplanets'' - those that orbit stars other than our sun, the scientists said in a briefing last Tuesday. They define this new class by the planets' smaller mass - roughly 14...