CLUSTER SATELLITES
ESA

A study of radio chirps and whistles blasting from Earth's magnetic field—sounding a bit like the famous Star Wars droid R2-D2—may help astronomers devise new ways of searching for planets orbiting distant stars.

U.S. astronomers used data from the European Space Agency's (ESA) Cluster satellites to track auroral kilometric radiation (AKR), radio emissions that accompany the dazzling lights of the auroras around Earth's polar regions.

The team from the University of Iowa in Iowa City found that the radio chirps fan out from starting points in the atmosphere in a narrow plane rather than a cone shape, as was long expected.

AKR, discovered in the 1970s, is believed to result from charged particles originating in the sun that spiral around magnetic field lines in Earth's atmosphere. These are the same solar wind particles that generate the aurora at a height of about 60 miles (100 kilometers) above the surface of the planet.

To home in on AKR emissions, researchers analyzed 12,000 bursts recorded by the Cluster mission, a group of four craft orbiting the planet in formation.

They traced the origins of the pulses to areas in the upper atmosphere measuring a few tens of kilometers wide and located thousands of miles (kilometers) above where auroras form. The results were published in a recent issue of Geophysical Research Letters.

Earth's upper atmosphere blocks the emissions from reaching the ground, which is a blessing for radio broadcasters because they are 10,000 times stronger than those human technology can achieve and would easily jam our broadcasts.

Spacecraft have also spotted auroral lights and AKR coming from Jupiter and Saturn. ESA said it may be possible that future radio telescopes could use the signals to study our neighboring gas giants as well as to locate and study similar planets around other stars.