“The only true voyage of discovery … would not be to travel to new lands, but to possess other eyes.”
I was fortunate to have a particularly close involvement with one of the most extraordinary scientific instruments at the Pole, or for that matter on the planet, the IceCube Neutrino Observatory.
Unlike the other astrophysical observatories at the Pole, all of IceCube's vital detection devices are invisible and inaccessible. In fact, they are buried up to 2.5kms deep in the ice of the Polar plateau. As I've mentioned, the Pole is quite high in altitude (9,300ft/2,800m), but the extraordinary thing is that below the surface, the ice extends all the way down to sea level, almost 3km down. The other extraordinary thing about the ice is that it's incredibly clear - clearer than crystal glass, clearer than distilled water, in fact, it's the most transparent solid known. Below 1.5kms down the pressure is so great that the trapped air bubbles that give ice its milky opacity dissolve into the crystal matrix of the ice and the transparency increases dramatically. This is the main reason the Pole was chosen for the Neutrino Observatory - but to explain that more fully I'll have to cover some basics.
This is a blog, not a physics textbook, so I'll try to be brief. Neutrinos are elementary subatomic particles that interact with other matter only through the weak subatomic force which is responsible for radioactive decay, and which plays an essential role in nuclear fission. The weak force is one of the four forces of the "standard model" along with gravity, electromagnetism, and the strong force (which binds quarks together to form protons and neutrons). The weak force is so named because it is orders of magnitude weaker than either the electromagnetic or strong force and operates at very close range only.
Neutrinos have no charge (and so are not affected by the electromagnetic force) and have minuscule mass (and so are practically immune to gravity). Consequently, they have to essentially collide with another subatomic particle to have any effect on it. This results in the wonderful (and frustrating) property that they hardly ever interact with other matter at all. They are created through radioactive decay and other subatomic interactions (weak interactions) and are created in huge quantities in the sun, the atmosphere and core of the earth, and in high energy cosmic events such as novae, super-novae and gamma ray bursts. They are in fact the commonest particle in the universe (there are a billion for every atom of matter), but also one of the least interactive and so are surprisingly difficult to detect. Some 60 billion of them pass through each of your fingernails every second - none of them having a single interaction on the way. In all probability, in your lifetime only one of those billions and billions of neutrinos passing through your body will interact with an atomic nucleus - smashing it apart, but in all likelihood not causing any noticeable effect.
Ray Jayawardhana in his fascinating book "Neutrino Hunters: The Thrilling Chase for a Ghostly Particle to Unlock the Secrets of the Universe" says, "Neutrinos travel right through the Earth unhindered, like bullets cutting through fog. Besides, the Earth’s bowels generate neutrinos, as radioactive elements decay, and so do collisions of energetic particles from space in the upper levels of the atmosphere. Cataclysmic deaths of massive stars set off tremendous bursts of neutrinos, which escape these sites of mayhem unscathed and bring us news of awesome celestial events millions of light-years away. Moreover, our planet is immersed in a sea of cosmic neutrinos, which sprang forth when the infant universe was barely two seconds old."
The only way they can be detected is to have a huge detector so that the exceedingly rare probabilistic event that they will interact with a proton will happen often enough for us to be able to record them. This is where the South Polar ice cap comes in. The IceCube array occupies a cubic kilometer of ice at the Pole. Such a huge volume of ice ( 1 million cubic meters) captures several hundred neutrino interactions every day.
I've already mentioned that the IceCube Neutrino array occupies a cubic kilometer of ice at the Pole. Specifically, the array consists of 5,160 photo-sensitive "Digital Optical Modules" or DOMs arrayed on 86 vertical "strings" that have been drilled into the ice. The strings are in a hexagonal grid spaced 125 meters apart and each string holds 60 DOMs spaced 17 meters apart. The logistics involved in creating the array are impressive. Between 2003 and 2011 close to 5 million pound of cargo were shipped from all over the world to the South Pole, requiring 181 LC-130 flights. That's a remarkable feat in itself but just add in the paperwork, the freight handling to get everything to Christchurch before the LC-130's are even loaded, and then the fuel and man-hours to make it all happen! Each bore hole required two days of constant drilling, and 4,800 gallons of gasoline to create, melting 200,000 gallons of ice in the process. At its completion in 2010, the Observatory had cost US$279 million.