No commercial airline flies to the South Pole. Instead, I started my trip there on a U.S. Air Force C-17 transport, which traveled from Christchurch, New Zealand, to McMurdo Station, a U.S. Antarctic research center located on the southern tip of Ross Island. I stayed at McMurdo overnight before boarding a smaller plane, an LC-130 turboprop, for the rest of the journey. After a 3-hour flight over the Transantarctic Mountains, my plane landed on skis at the bottom of the world.
Stepping off the LC-130, I found the cold, thin air a real shock—the South Pole is more than 2800 meters above sea level, and the temperature was –30 °C. I staggered to the shelter of South Pole Station, from which, after suiting up in 10 kilograms of extreme-cold-weather gear, I walked to the nearby drilling camp. The goal of this operation was to bore holes 60 centimeters in diameter, each reaching about 2.5 kilometers below the surface, which is deeper than the Grand Canyon.
In 2005, a year before my visit, technicians had drilled the first of 86 holes. Initially, each one took 57 hours to make, using a jet of hot, pressurized water. By the time I arrived, the drillers had honed their technique, and the same task took 40 hours of work, weather and equipment permitting.
On the morning of 18 December 2010, the drill burrowed into the ice one final time to complete the last hole. These holes are now the permanent homes for strings of exquisitely sensitive light detectors, which more than 200 scientists, engineers, and technicians from nearly 40 institutions—including my own, Lawrence Berkeley National Laboratory (LBNL)—will use to search for signals from the far reaches of the cosmos.
We hope to solve a mystery that came to light 100 years ago, when Victor Hess, a physicist at the Institute for Radium Research of the Austrian Academy of Sciences, climbed into a hot air balloon. He wanted to measure radiation at high altitudes. Scientists had discovered this radiation—what physicists now understand to be a sporadic flittering of subatomic particles—almost everywhere they looked. Some attributed it to radioactive elements in the ground, and Hess wanted to test that theory. He took off into the air, eventually ascending 5000 meters. As Hess climbed, he saw an increase in the radiation he was measuring. That meant it wasn’t coming from Earth. Nighttime readings were no lower, which ruled out the sun. He concluded that the origin was likely somewhere deep in space. Hess’s discovery of what were later dubbed cosmic rays won him a Nobel Prize in Physics, in 1936. Although Hess’s work encouraged researchers to focus on the heavens, he was unable to determine the exact source of these energetic particles. Today astronomers and physicists still debate the possibilities.
Very likely, some of these cosmic rays originate within our own galaxy, accelerated in the magnetic fields and dense plasma that stars produce when they reach the end of their lives and explode, forming black holes or neutron stars. More energetic cosmic rays probably have more violent births, within jets spewed from the disks of matter surrounding ultramassive black holes at the center of other galaxies; during the collapse of a giant star, 100 or more times as massive as our sun; or in a collision between two black holes or between a black hole and a neutron star.
Scientists can easily detect the charged particles in cosmic rays using any number of simple detectors—even photographic film. And they have: By the 1930s, physicists had measured coincident signals using instruments separated by hundreds of meters. They realized that the background radiation that perplexed scientists of Hess’s time could come from high-energy, charged cosmic-ray particles that strike nitrogen or oxygen atoms in Earth’s atmosphere and create in each collision a shower of low-energy particles. By the 1960s, they knew that these downpours could include billions of particles, spread over many square kilometers. But figuring out the starting point of the original cosmic ray requires a more sophisticated approach. Any matter or magnetic field that a charged particle encounters during its interstellar journey alters its trajectory, making it hard to determine its origin.
But cosmic rays also contain uncharged particles called neutrinos, which travel more determinedly. Magnetic fields don’t affect them, and they barely interact with matter, meaning that they can course unhindered through the thickest clouds of cosmic dust and gas. Because the path of a cosmic-ray neutrino points straight back to its origin, astrophysicists dearly want to trace the trajectories of these particles.
Unfortunately, the same characteristic that allows neutrinos to travel with little interference makes them nearly impossible to detect. Only very rarely will one crash into matter and create a cascade of other, more easily detectable charged particles. To witness that, researchers must be either extremely lucky or need to monitor a big target—for example, a 1-cubic-kilometer chunk of Antarctic ice.