When Antarctica was first explored it was quickly obvious that it did not have much potential for commercial or industrial activity. It was simply too remote, too barren, and too cold. Consequently most Antarctic activity has had a scientific focus; this was true of early expeditions like Scott’s, and it is certainly true today.
Today there are a handful of permanent Antarctic research stations, some located near the coast and others, such as the Amundsen-Scott Research Station, which is at the South Pole itself, well inland. Scientists are interested in the biology, geology, vulcanology, and meteorology of the place. Its pure ice cores provide a good way to study the history of earth’s climate. Its high altitude and clear atmosphere make it appealing for astronomical observation (as at the South Pole Telescope).
But there is one modern Antarctic experiment that surpasses all others in the vastness of its scale and the beauty of its conception, and it is that experiment that I would like to highlight today: IceCube, the South Pole Neutrino Detector.
IceCube is a new project; its five-year construction period was completed only in December 2010. Its principal goal is to study ultra-high energy neutrinos originating from astrophysical sources. In that sense it can be thought of as a neutrino telescope. (A neutrino, if your physics is rusty, is a subatomic particle similar in some respects to an electron but without electric charge that interacts very weakly with other matter.) Neutrinos are produced in radioactive sources. The vast majority of the neutrinos around us — and there are billions of them passing through our bodies every second — come from the sun, but there are also some from other astrophysical objects. For some time now there has been a mystery about a class of neutrinos that have been measured to have very high energies, far higher than we would have thought likely, or even possible. Where do they come from? What kind of physical process produces them? IceCube is going to try to detect these high energy neutrinos and identify the direction from which they come. If they seem to be coming from a few specific points in the sky, we can then take a closer look at those points using more conventional telescopes.
Why build the detector at the South Pole? The reason is that the only way to detect a neutrino is to pile a whole lot of stuff in front of it and hope that the neutrino will hit the stuff. If it does (and if certain conditions are satisfied) a brief flash of light, called Cherenkov radiation, will be produced, and this light can be detected.
The brilliant idea behind IceCube is to use Antarctica itself — and, more particularly, its immensely thick ice layer — as the stuff. Accordingly, scientists have drilled 2-1/2 km down into the ice and sunk strings of sensitive light detectors down the shafts. The detectors simply sit there, waiting, until a neutrino interacts with an atom somewhere in the ice, and then they measure the flash of light that is produced.
This sort of experimental design is not new; detectors such as Japan’s Super-Kamiokande and Canada’s Sudbury Neutrino Observatory (SNO) are built on the same principles. What is special about IceCube is its incredible scale: the ice shafts are distributed over an area of roughly one square kilometer, and the strings of detectors are roughly one kilometer long. In this way, the scientists have instrumented an ice volume of about one cubic kilometer. IceCube is about 20 000 times larger than Super-Kamiokande, and over a million times larger than SNO. Even with this massive volume, however, the detector is expected to detect only one neutrino every 20 minutes or so; all of the other gajillions of neutrinos passing through the ice every second simply coast on through without hitting anything. As I said, neutrinos interact very weakly with matter.
There are not many scientific results from IceCube yet — the 400 papers already published are mostly, it appears, about its construction, testing, and potential — but it is definitely a project to watch. Wikipedia lists a number of its experimental objectives in plain language, and a more technical overview is available from the IceCube collaboration itself. For me the most amazing things about IceCube are the sheer audacity of the concept, and the fact that it has actually been built. It is all quite wonderful.