In May 2017, I accepted a job offer at the Wisconsin IceCube Particle Astrophysics Center (WIPAC) in Madison - a job that will send me to the bottom of Earth. IceCube is a giant Neutrino detector at South Pole, and it will be my job to keep its computers running. For an entire year (November 2017 to December 2018) I will live and work at the Amundson-Scott South Pole Station in Antarctica. Being an IceCube "Winterover" has been my dream job for years - und now the dream is real. This page is my journal of this once-in-a-lifetime adventure.
Most of the content will be in English, but I might write in German occasionally. The journal entries are sorted by date (latest first).
It's finally boring enough down here so that I can start writing about science. ... Nah just kidding, this is gonna be awesome! Because science is awesome! Science yeah! SCIENCE!
As you might know, I was hired as an astroparticle physicist to watch over the IceCube Neutrino Telescope here at South Pole. The name itself poses a bunch of questions already: What are neutrinos? How is IceCube a telescope? And why at the South Pole?!
Let's tackle the first question today and learn about neutrinos. They are very fascinating little guys, that live in the lepton family of the Standard Model of Particle Physics which is visualized on the right. The model holds all elementary (that means indivisible, unlike neutrons and protons or whole atoms) particles that we know of today: The quarks, which are the building blocks for protons and neutrons and therefore all matter we see around us. The gauge bosons, which are the carriers of the four fundamental forces - gravity, electro-magnetism, strong force and weak force. The recently discovered Higgs boson which "gives" mass to other elementary particles in the model. And the leptons, which are, among other things, defined over their 1/2-integer spin. For each quark and lepton, there exists an antiparticle with identical mass but opposite electrical charge.
The best known lepton is probably the electron, which per definition has an electric charge of -1 and can form atoms together with protons and neutrons. The muon and the tau are pretty much just heavier electrons. For each of these three there exists an uncharged counterpart, the electron-, muon- and tau-neutrino, represented by the greek letter υ. We know about them only since they were postulated by Wolfgang Pauli in 1930. Why? Because they're incredibly hard to find. Elementary particles are so tiny that we can only "see" them when they interact with things, like an electron being pushed around in a magnetic field. Neutrinos however do not take part in electro-magnetism, because they do not carry electric charge, unlike their lepton brothers. They only reveal themselves in interactions of the weak force, which - you could say - is the "rarest" of the forces (also pretty complicated, so let's cover that in a different session). "What about gravity?" you might ask. Well, technically you're right, but the neutrino masses are so incredibly small that gravity basically has no impact at all, at least not on a scale we could measure. Fun fact: According to the Standard Model, the neutrinos should be completely massless. Nowadays we know they actually do have tiny masses, although the exact values are still a mistery. Their property of being a pain in the butt to find, and the fact that we still do not know a lot about them, awarded the neutrinos the nickname Ghost Particles.
So why do we care about neutrinos? First of all, because they're there (which, for a physicst, is an absolutely sufficient but not necessarily required condition :D)! Second of all, they are considered ideal cosmic messengers. What does that mean?
Well, neutrinos are not influenced by cosmic magnetic fields, neither are they likely to interact with anything like dust clouds or radiation - so they basically travel through space in a straight line unimpressed by whatever may try to deflect them from their path. The highest-energy neutrinos originate in powerful cosmic objects like supermassive black holes or active galactic cores, so they carry precious information from the very inside of these objects with them. No other particle can do that. Neutrinos are the unicorns of space!
Science facts #5 Solar shenanigans
To understand what's going on in this week's science facts, you need the following vocabulary:
Solstices happen twice a year; they are defined as the days the sun reaches it's respectively highest (in the summer) or lowest (in the winter) altitudes in the sky.
Equinoxes are the two days of the year when day and night are of exactly the same length. At the poles, the equinoxes are the moments of sunrise and sunset.
Earth's rotation axis is tilted about 23.5° relative to the perpendicular to its plane of movement around the sun. That's the reason for seasons on our planet! It's also the reason for night and day at South Pole - if the axis wasn't tilted, Amundsen-Scott South Pole Station would be at the edge of dawn year round. But because things are how they are, we get one long day and one long night. The ostensible movement of the sun across the South Pole sky is illustrated in the picture below: It basically draws big circles seemingly without change in altitude every "day", with those circles slowly moving towards or away from the horizon. The sun's highest point in the sky is at summer solstice and measures 23.5° from the horizon, which equals the tilt of Earth's rotation axis - makes sense, doesn't it? It's hard to wrap your head around it at first, but maybe it helps to look at how the sun "moves" right at the equator: It rises and sets exactly perpendicular to the horizon every day of the year, with its highest altitude at the zenith straight above your head on the equinoxes, and its lowest altitude about 66.5° (= 90° - 23.5°) either from the north or south horizon on the solstices.
The polar day therefore is equivalent to the polar summer, as the polar night is to the polar winter. The nicest consequence of all this: Sunrise and sunset both seem to take about a week! If the weather is not shitty (which it might be according to our meteorologist Janelle) I'll show you some awesome photos next week.
Fun fact: The average time of daylight per 24 hours is exactly 12 hours for EVERY place on Earth, even the Poles. It makes sense if you think about it! :)
Science facts #4 The IceCube Laboratory
I guess it's about time to talk about my actual job a little bit again. But before I tell you what exactly it is that I do (because I like messing with people who keep asking me that exact question ;)), let me show you my workspace! The IceCube Laboratory, or short ICL, is located in the dark sector* (I know, right?!) about a kilometer away from Amundsen-Scott South Pole Station. It marks the center point of the IceCube detector which is buried under 1.5 km of ice. All the hundreds of miles of cables that IceCube consists of come together in this little building. Those arm-thick cables enter the ICL through the two large cable towers you can see in the picture above, and are split up inside into smaller red quad cables which each are connected to four DOMs deep down in the ice; their other ends are connected to the DOMHubs, custom-made computers that feed high voltage to the sensors and read their data in return. We've got 97 of those! All the other machines (we've got a total of about 200!) are data processing or infrastructure machines, that means they filter and pre-analyse the data, they host important resources like repositories, mail accounts, or the detector monitoring system, or are responsible for the Iridium connection that lets the winterovers communicate with the North during satellite outages.
So yes, the essence of IceCube is housed in the little blue building in the middle of nowhere - it's cozy, and the noise of all the machines has a somewhat soothing effect on me by now. The dog house, the little blue cube on the roof, is a perfect get-away when you need a break from life on station. I'd spend way more time out there, if the ICL would feature a bathroom with running water...
Fun fact: The ICL is THE ONLY building at South Pole that has to be actively cooled. For that purpose the outside air is sucked in, heated up (yes, we're at South Pole), and blown into the server room. If the air conditioning shuts down for only 20 minutes, the exhaust heat of our computers heats the server room up to almost 60° C - which can be fatal for all kinds of expensive equipment in there! That's why we monitor the temperature very closely with dozens of sensors.
* I will explain South Pole's sectors in a later post, promise :)
Science facts #3 Askaryan Radio Array (ARA)
The Askaryan Radio Arrary ... pardon me, the Askaryan Radio ARRAY is a sister project of IceCube. Like the Cube, it is also looking for high energy Neutrinos, but instead of optical sensors it utilizes radio antennas to detect our favorite particles. The measurement principle of ARA is based upon the Askaryan effect, which describes the generation of charge anisotropies in bulk media (such as ice) caused by high-energy neutrino induced particle cascades. The anisotropy emits coherent radio waves which can be detected by the ARA antennas.
At the end of this summer season, the experiment will consist of six stations with four holes each, where every hole is holding 4 antennas. Once completed, ARA will cover an area far bigger than IceCube, although with a far smaller detector density. It's neutrino detection sweetspot is at energies even higher than IceCube's, which makes it an important addition to the South Pole Neutrino Club.
Science facts #2 IceTop Snow Measurements
If you paid attention in my IceCube facts #1, you might have noticed that IceCube does not only have in-ice optical sensors to measure the neutrinos, but also features some modules right beneath the surface - these are called IceTop stations. Each of the 86 strings that are deployed in the ice has one of them on top. All together, the IceTop stations are used to measure lower-energy neutrinos, and they also serve as a veto-mechanism for the in-ice DOMs. The problem with stuff that is set up at the surface of South Pole ice plateau: It does not stay at the surface for very long. Things are being burried in snow drift faster than you can say "penguin". Since the amount of snow that covers IceTop has an affect on the measurements, every once in a while the IceCube winterovers have to go out and estimate the snow level on every single IceTop station. This can be a long and cold adventure, depending on the windchill and how many people can be motivated to help. Fortunately, the old winterovers Martin and James were still here (they belong to the handfull of toasty people who are still waiting for a plane to take them back to the real world) to help Johannes and me, so it took us only two afternoons.
Science facts #1 The IceCube detector
The IceCube South Pole Neutrino Observatory is a huge particle detector burried in the almost 3000 m thick Antarctic ice sheet at South Pole. IceCube is looking for ultra-high-energy neutrinos. Upon colliding with the atoms of the ice, these tiny particles produce a little flash of blue light. This is called the "Cherenkov effect". The light can be seen by IceCube's thousands of optical sensors, which have been deployed on long chains by drilling deep holes in the ice. The data collected by these sensors is sent to the surface, where it is recorded and forwarded to the Northern hemisphere for analysis.
To get a better idea of IceCube, you can have a look at the picture below (courtesy of the IceCube collaboration) or visit icecube.wisc.edu.