The second year of an unprecedented balloon campaign in Antarctica has just begun. The NASA-funded mission - called the Balloon Array for Radiation belt Relativistic Electron Losses, or BARREL - is led by Dartmouth College in Hanover, N.H. The mission is unique, as it relies not on one gigantic balloon, but on many smaller ones, 20 in total.

BARREL's job is to help unravel the mysterious radiation belts, two gigantic donuts of particles that surround Earth. The mission works in conjunction with NASA's Van Allen Probes, two spacecraft currently orbiting around Earth to study the belts.

"This year the Van Allen Probes and the BARREL balloons will be exploring what happens at dusk," said Robyn Millan, principal investigator for BARREL at Dartmouth.

"Balloon campaigns in the Antarctic region have long seen these bursts of particles precipitating down toward Earth at dusk. This year, the spacecraft and the balloons will have coordinated measurements to determine what's happening up in the belts during these events."

Millan and her team traveled to Antarctica in mid-December 2013, and they launched their first balloon on Dec. 27, 2013.

They will launch a single balloon on any given day, which will float leisurely around the South Pole for up to a week or two afterwards. Instruments aboard the balloon will send back data on the magnetic systems it floats through, as well as the kinds of particles it observes.

By coordinating with the Van Allen Probes data, orbiting high above, the team hopes to determine what's happening in the belts that correlates with the precipitation bursts near Earth. Such information will ultimately help scientists understand how particles get ejected from the belts.

"The spacecraft will be taking measurements in the right place to observe the radiation belt environment during these precipitation events," said Millan. "We should be able to tell what is causing these events, and that is really one of the main goals of BARREL."

In addition to Dartmouth, the BARREL mission is supported by scientists from University of California-Berkeley, the University of Washington and University of California-Santa Cruz. Field operations are being conducted at the British research station Halley VI and the South African research station, SANAE IV.