Unlike, say, Mars's or Venus's, Earth's atmosphere was thought to be untouchable inside our protective magnetic field. But a new study says the sun is slowly "stealing" our atmosphere -- and at a greater rate than on Mars or Venus. Mars, for example, probably started out with a thick atmosphere similar to Earth's. But without a magnetic field to protect the Martian atmosphere, the solar wind -- actually a stream of charged particles from the sun -- has been eroding it away. Venus also lacks a magnetosphere and is being stripped of its atmospheric covering. Currently its rate of loss...