A NASA satellite has recorded a surprisingly large flow of water out of Earth's atmosphere. The results, reported in the current issue of Science,* should shed light on the forces that cause damaging electromagnetic storms and other space weather phenomena.
Launched early last year, the POLAR satellite measures the polar wind, charged particles flowing from Earth's atmosphere into the magnetosphere. Past attempts to measure such plasmas have been hampered by the fact that satellites sitting in sunlight acquire a charge that repels the particles they are trying to detect. But POLAR contains a device that bathes the craft in a wispy cloud of ionized xenon, neutralizing the charge and allowing the instrument to measure ions flowing from Earth's atmosphere. "These are much better data than before," says Tamas Gombosi, a space physicist at the University of Michigan, Ann Arbor.
POLAR's results have surprised experts, whose views are based on 3 decades of observations and modeling. The daily flow of hydrogen and oxygen ions was measured at 3785 liters of water, an amount greater than most models had predicted. In addition, the oxygen ions were found to be hotter than expected. "The theory was that there was very little oxygen outflow," says team member Thomas Moore, a geophysicist currently at the NASA Goddard Space Flight Center in Greenbelt, Maryland. "Clearly, the implication is that there's more energy going into these plasmas than the theory involves."
Not only does the research give atmospheric scientists a better idea of what is escaping from the atmosphere, it should help them understand some of the triggers for electromagnetic interference in the sky. "These are the processes that make geomagnetic storms and turbulence," says Moore. "They knock out satellites and disturb power grids and communication systems. They have an impact on human activities in space and on the ground."