Scientists leading the consortium building the massive neutrino detector said they have nearly doubled its size, at its site at the National Science Foundation's Amundsen-Scott South Pole Station.

The work can take place only from October through February � during the summer season at the Pole � but the extent and pace of construction has convinced the scientists they soon could begin operations, although IceCube is not scheduled for completion until 2011.

"The news is good all around," said team leader Francis Halzen of the University of Wisconsin.

IceCube - which depends on strings of light-sensing modules frozen deep in crystal clear Antarctic ice � grew by 480 basketball-sized optical modules this past season. Deployed on long cables in 1.5-mile deep holes bored by a hot-water drill, the modules will be used to detect the fleeting signatures of high-energy cosmic neutrinos as they flit through Earth's mantle and core.

Neutrinos are ghostly, high-energy subatomic particles created in galactic collisions, distant black holes, quasars and the most violent events in the cosmos. They carry information that promises to peel back some of the mystery of the universe's most enigmatic events such as gamma ray bursts, dark matter and supernovas.

Cosmic neutrinos - billions of which pass unnoticed through the Earth every day - are by their very nature extremely difficult to detect. They require a very large detector to improve the chances that scientists can catch a neutrino in the act of crashing into a proton or another subatomic particle.

When IceCube is completed, it will be seeded with more than 4,200 optical sensors in an attempt to capture telltale traces of the neutrinos and follow their tracks back to their distant points of origin. Scientists plan to deploy another 300 or so sensors in tanks on the surface of the polar ice.

As soon as all of the holes are drilled, cables with the spherical digital optical modules - composed of electronics for sensing light and circuit boards for gathering and processing data � will be lowered into the ice, where they will be frozen in place. The modules act like light bulbs in reverse, gathering light created when neutrinos collide with other particles. The modules then relay data to the surface, where the information is processed and stored for analysis.

When fully operational, the Antarctic IceCube actually will sample neutrinos from the sky in the Northern Hemisphere, using Earth as a filter to exclude other types of neutrinos, such as those from the Sun, which could confuse the detector. Its primary scientific mission is to identify the sources and distribution of the highest energy neutrinos created by violent cosmic events.

IceCube is being constructed around an older prototype neutrino detector called AMANDA - for Antarctic Muon and Neutrino Detector Array. IceCube construction began in January 2005, when scientists drilled the first hole for the detector and deployed the first optical modules for the observatory.

"The digital optical modules deployed last year have now functioned for one year without failures," Halzen said. "They perform like a Swiss watch. But the big story of this season is the performance of the drill."

After working out kinks in the performance of the drill last year, and again at the beginning of the 2005-06 drilling season - and adding an extra drilling tower - the IceCube team bored a total of eight new holes and deploy eight 60-module sensor strings. Combined with the existing AMANDA array, IceCube currently consists of nearly 1,300 optical modules.

"All the major challenges encountered by drilling a first hole last season have been solved," Halzen said.

The IceCube array now comprises nine strings and 16 surface detector stations, in addition to the still operational AMANDA array, said Jim Yeck, the project's director. "We know that there is more work to be done," he said, "but let there be no doubt about what a remarkable accomplishment it is to safely install eight strings this season."

Yeck said the newly installed modules are functioning and sending signals to the surface. IceCube scientists will continue to verify cable connections and surface electronics during the upcoming winter season at the South Pole.

NSF, through a joint program of its Office of Polar Programs and its Mathematical and Physical Sciences Directorate, is contributing more than $240 million to the international partnership that is building the detector, which will cost $272 million overall.

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