Cosmic chorus causes Earth's magnetic field to hiss

A study says a cosmic chorus, thousands of miles above Earth, is filling the heavens with a mysterious, low frequency "hiss."

Scientists, studying data from a set of NASA probes designed to monitor substorms which are dramatic exchanges of energy among charged particles that spark the auroras at Earth's poles, have determined that the charged particles come from the sun and get trapped in loops around our planet by Earth's magnetic field. If it was known how the hiss influences the loops, the Van Allen radiation belts, this information may help scientists predict their behavior which is desirable because the belts can bombard satellites, spacecraft, and even spacewalking astronauts with dangerous radiation. The charged particles come from the sun and get trapped in loops around our planet by Earth's magnetic field. At present, we are experiencing an unprecedented lull in solar activity, space is expected to get much stormier after 2012, when the sun should enter an active phase that will hurl more charged particles toward Earth. The plasmaspheric hiss, which manifests as a faint "shh" sound, is the result of an electromagnetic wave in Earth's radiation belts. The hiss wave appears to reduce levels of dangerous electrons in the radiation belts by deflecting the particles from their stable trajectories and sending them into the dense upper atmosphere, where they are lost. For over fourty years,scientists have been puzzled by what was generating the hiss wave. A previous model had suggested that the hiss wave might evolve from a more distant radio wave called chorus, so named because its discoverers in the 1950s thought it sounded like "a rookery of birds heard from a distance," Bortnik said. It was difficult to find proof for this idea presented and researchers would need simultaneous, high-resolution observations from two sophisticated satellites recording both hiss and chorus from different locations at a moment when Earth's magnetic field was particularly active. One of Bortnik's students stumbled upon exactly what they needed in data from two of NASA's five THEMIS satellites. "We didn't think that we'd be lucky enough to get this kind of gift from nature," Bortnik said. The probes showed a definite correlation between the two waves and confirmed the hiss wave comes from chorus. Understanding the hiss wave's origins could allow scientists to build more accurate models of the radiation belts, which could ultimately help predict space weather. Studying space weather is similar to studying weather patterns here on Earth. "Step number one is just to understand the system," he said, and then maybe there's hope that researchers can predict things in time to avoid danger.