IceCube Telescope Takes Shape Below Antarctic Ice

PabloSandoval48 writes "The world's largest telescope, currently under construction more than a mile beneath the Antarctic ice, is on schedule to be completed next year, according to a researcher at the University of Wisconsin, the lead institution for a scientific project called IceCube."

Not a telescope

[wagnerrp]

This is an observatory, but not a telescope. It's an omnidirectional particle detector, not pointed at some distant star.

Re:IceCube?

[zero.kalvin]

You are taking about Baikal, it's a similar but on smaller scale. The Russians are hoping to join KM3NET in the future.

Re:But...

[Anonymous Coward]

IceCube is a neutrino telescope which looks through the Earth to the Northern Hemisphere. The Earth basically acts as a filter removing potential background signals.

Re:Not a telescope

[zero.kalvin]

It's the equivalent of telescope with a view range of 4*PI. You are looking everywhere at the same time.

Re:Telescope?

[Steve Max]

Why? It captures information from a flux of particles (not photons, but neutrinos in this case) emitted by astrophysical objects. It allows us to study properties of those objects (and of the detected particles as well). It doesn't have a resolution high enough to give us an "image" of most of those objects, but Hubble can't image most single stars too. IceCube won't give you a pretty picture for APOD, but it will do everything else we can do with an optical telescope, or a charged particle telescope such as Auger [auger.org].

Re:Interesting...

[zero.kalvin]

As someone working in this exact field I would say no. Where are you going to put it ? The idea of burying it deep in a refracting medium is to eliminate cosmic rays as background noise, and allowing the neutrino to produce a muon which will do a Cherenkov light in the detector. You need a deep refracting medium for this, beside we use the whole earth as a detector because of the low cross-section the neutrino have. So with a smaller stellar body(the moon) you will have less neutrinos interacting, and this less data to work with.

Re:World's largest, eh?

[Anonymous Coward]

One cubic kilometer is not 1000 cubic meters.

Re:World's largest, eh?

[John Hasler]

> This thing has a volume of about 1,000 cubic m.

1 cubic km. That's 10E9 cubic m.

Re:World's largest, eh?

[atrain728]

It probably doesn't count because it's smaller.

Muons, not neutrinos

[mangu]

they've seen the moon already, as a deficit of neutrinos coming from the moon's direction.

There's a deficit of muons, not neutrinos, from the moon's direction. Neutrinos pass through the moon easily.

Re:Interesting...

[radtea]

Would there, however, be any benefit to having such a project set up under lunar regolith/base rock if we could ever get back to the moon?

Yes.

The reason why: there are virtually no high-energy muons in lunar cosmic rays, and high-energy muons, one way or another, are the major cosmic-ray background in these experiments.

The reason why there are virtually no high-energy muons in lunar cosmic rays is due to their primary mechanism of production: on Earth, cosmic-ray protons smack into atoms at the top of the atmosphere, producing high energy pions, which decay into muons etc... and because of the low density of the atmosphere, the decay time is much less than the stopping time, so the muons have most of the orignal energy of the primary cosmic ray available to them.

On the Moon, which notably lacks an atmosphere, the primay cosmic rays smack into the lunar regolith and therefore the pions are created in a very dense medium, and lose most or all of their energy before decaying. The muons thus created are relatively low energy and stop within a few meters--as opposed to terrestrial cosmic ray muons which are still seen in experiments like the Sudbury Neutrino Observatory, 2 kilometres underground.

As such, a relatively small, relatively shallow detector on the Moon could produce comparable performance to the best terrestrial detectors, at only a few orders of magnitude higher cost.

It may be worth mentioning that no one working in the field ever calls a neutrino detector a "telescope", as in English that word when used without qualification virtually always means "optical telescope", so the usage in this article is misleading and confusing, to the point where if were done deliberately I would consider the person doing it to be either stupid or dishonest. I guess maybe the person who wrote the article or provided the information for it has English as a second language.

Re:It is a big problem

[zero.kalvin]

I did not say they have a big rate of failure. By detectors you mean OM, or optical modules. Optical modules are attached to each line. This problem can't be solved by compensating in the software. if you put your lines to close you will start having problems of the light produced by the muons not reaching other OMs and getting blocked very soon. Spacing is required as there is already few photons to work with. If an OM is out, it's over. if they have an electrical failure on one of the lines, it's over for that line. When it was on the sketch board, they took this in consideration, that's why it's big and with so many lines and OMs. But I repeat if it's out, it's out.

Re:Not a telescope

[IceCubeComm]

An event reconstruction from the 79 string detector configuration https://blog.icecube.wisc.edu/?p=1355 [wisc.edu]

Re:But...

[Deep Penguin]

But that's what it sees - the sensors point at the Earth and the filter software discards muon events that track from the sky, keeping events that come from underneath since muons coming from the Northern Hemisphere decay long before they can reach the detector. Neutrinos survive passing through thousands of miles of rock, so if it comes from the middle of the Earth, it's a neutrino. If it comes from the sky, it could be a neutrino, but chances are, it's a muon.

Re:World's largest, eh?

[Anonymous Coward]

> This thing has a volume of about 1,000 cubic m.

1 cubic km. That's 10E9 cubic m.

No, 1E9 cubic meters.

Re:Interesting...

[kievit]

I agree that the background reduction due to lack of atmosphere is very convenient, but as zero.kalvin points out, you still need a 'refracting medium', that is, a really large volume of transparent material such as water or ice (in which you can catch the Cherenkov light whenever a neutrino is kind enough to interact and produce fast charged particles). The large volume is not needed to suppress background, but to beat the very small cross section; in order to detect neutrinos you need them to interact with your detector, and the only way to achieve that is to make it as big as possible.

There is ice on the Moon, but to harvest that and turn into a detector poses some interesting challenges. To use it in frozen form is hard, because you need it with a clarity and purity similar to the exceptionally clear deep Antarctic ice that IceCube uses and which is even clearer and purer than laboratory ice. To use it in liquid form requires keeping it heated, which is probably easier (you need a solar panel farm to power the heating system, but for the ice option you would also need those panels, to power the elaborate purification system + clear ice machinery). Either way: probably science fiction.

Re:Muons, not neutrinos

[Deep Penguin]

Not all the neutrinos, just nearly all. The moon is large enough to catch a statistically discernible (to IceCube) amount of neutrinos, casting a "neutrino shadow" on the Earth.

Re:Interesting...

[zero.kalvin]

Actually yes, the near vacuum condition will help a lot on the angular resolution. But you will run into a lot of problems: The near vacuum conditions will mean that for the muon to create a Cherenkov light cone it would have to be hyper-relativistic. Since the muons energy is about 33% of that of the neutrino, most Energy fluxs are decreasing with energy(negative power laws), and with a lower stellar mass(of the moon). You will detect far less events in general, specially in the lower energy region. If you can place your detector in a refracting medium(let's say water), with a reasonably sized telescope (1km3), I will let you do the calculation on how much water we will need, with all the electronics problem that are associated with it.

Re:Not a telescope

[Steve Max]

It's ability to trace the sky using a carrier that was never explored in this way (except to "see" what happens in the sun, and during a nearby supernova).

Using optical telescopes, we can get an image of how the universe looks in visible photons. In an x-ray telescope, we get an image of the universe in x-ray photons. In a cosmic ray telescope, we get an image in charged particles. IceCube (plus its northern sister, KM3Net) should be able to get an image of the universe in neutrinos with energies over 1 TeV.

Re:World's largest, eh?

[Bigjeff5]

The Hubble doesn't count because it's nowhere near the largest. It doesn't even make the top 50 list, more like around 55'ish. The Hubble gets great images because it is in space, and doesn't have to deal with atmosphere and light pollution. It can also catch wavelengths that are largely absorbed by the atmosphere, like infra-red and UV. That makes it extremely useful, however almost all of the ultra-long range research (~13 billion light years) is done with earth based telescopes and fancy corrective software to account for the affect of the atmosphere.

The two largest telescopes are each about four times larger than the Hubble.

Wait, why are we speculating?

[Chris Burke]

The IceCube website and U Wisc. [wisc.edu] says it's a telescope. So, case closed as far as I'm concerned.

Re:It is a big problem

[IceCubeComm]

Actually they call the individual detectors DOMs-Digital Optical Modules. Each string has 60 DOMs on it (plus 4 DOMs on the surface config IceTop) and altogether there will be 86 strings. Right now there are 79. Of course they calibrate, test, re-test before deployment, and troubleshoot when there are problems, but yeah if a DOM is out it's out.