Space, like Earth, has melodic dawn chorus

Artist's impression of the Cluster quartet, which has picked up a magnetic melody.

By Richard Stenger
CNN

(CNN) -- On Earth, tuneful chirps and peeps announce the beginning of each day. In nearby space, an uncannily similar chorus erupts each dawn, expressed by electrons instead of birds.

Of course, space is a vacuum in which nothing can be heard. But scientists, analyzing radio signals from a fleet of satellites, have picked up tones in the mornings that resemble the sounds of songbirds.

The dawn chorus is thought to be the work of highly energetic electrons, ensnared in the Earth's radiation belts. Scientists have heard the signals before, but only on rare occasions. They know little about how they form.

AUDIO Listen to the morning song of the magnetosphere. 45 sec. / 120.6k WAV sound

"The chorus is detected most on the Earth's morning side, but it's not clear why," said Craig Kletzing, a University of Iowa researcher who tuned in with the Cluster fleet, four European Space Agency satellites studying the Earth's magnetic fields.

The spacecraft, which travel in a tight pack along the same elliptical orbit, picked up the whistlers at their closest approach to Earth.

Cluster scientists think the use of the multiple satellites should help them find out more about the mysterious melodies, including from exactly where they originate.

"We can use the Cluster spacecraft to study how the radio waves spread from this region to different locations," Kletzing said last week. "Near their source, the radio waves are close together, so we can tie down their origin quite well if the Cluster spacecraft are also very close together, less than 200 km (124 miles) apart."

Preliminary Cluster data so far suggest that the whistler waves stream from the magnetic equator region and spread in opposite directions.

The identical Cluster satellites, Samba, Salsa, Rumba and Tango, were launched in 2000 and began the most detailed observations ever of the magnetosphere in February.

A magnetic bubble enveloping the Earth, the magnetosphere protects the planet from the solar wind, a perpetual stream of electrically charged particles emanating from the sun.