Cosmic radio waves mimic chirping of 'alien birds'

[Richard O'Neill]

By MARCIA DUNN | Associated Press | Dec 4, 2012 2:35 PM CST

Twin spacecraft have captured the clearest sounds yet from Earth's 
radiation belts -- and they mimic the chirping of birds.

NASA's Van Allen Probes have been exploring the hostile radiation belts 
surrounding Earth for just three months. But already, they've collected 
measurements of high-energy particles and radio waves in unprecedented 
detail.

Scientists said Tuesday these waves can provide an energy boost to 
radiation belt particles, somewhat like ocean waves can propel a surfer 
on Earth. What's more, these so-called chorus waves operate in the same 
frequency as human hearing so they can be heard.

University of Iowa physicist Craig Kletzing played a recording of these 
high-pitched radio waves at the American Geophysical Union meeting in 
San Francisco.

"Not only do you hear the chirps -- the alien birds as my wife calls 
them -- but you hear that sort of cricket-like thing in the background," 
Kletzing told reporters.

Before, those background sounds were inaudible.

"So this is really a fantastic new measurement," he said.

While the chorus has been audible even before the Space Age -- ham radio 
operators could sometimes hear it in decades past -- the clarity of 
these measurements is "really quite striking," Kletzing said.

Initial findings show the outer radiation belt to be much more dynamic 
and rapidly changing than anticipated, said the University of Colorado's 
Daniel Baker, principal investigator for the electron proton telescope 
on each probe.

The Van Allen probes -- formerly known as the Radiation Belt Storm 
Probes -- were launched from Cape Canaveral on Aug. 30. They were named 
after the late University of Iowa astrophysicist James Van Allen, who 
discovered the radiation belts that bear his name a half-century ago.

Recording of waves: 
http://vanallenprobes.jhuapl.edu/newscenter/intheloop/2012_0912.php