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How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .
This seems not very much. How do we know of them at all?
particle showers when one hits the upper atmosphere.
"That's no moon..."
"Win treats sysadmins better than users. Mac treats users better than sysadmins. Linux treats everyone like sysadmins."
Your mom is a visible light detector every time anyone looks at her.
Put differently, the moon is not being turned into a detector of anything, but "astronomers are building a telescope" is not a very catchy headline.
By being really clever! My father was a cosmic ray physicist and had a cosmic ray lab on top of Mount Evans (14000+ feet) in Colorado to detect these critters. I honestly don't know if he ever "captured" one, but he was awarded a Gugenheim fellowship to continue his research world-wide, and a number of his graduate students who suffered a winter on top of the mountain got their PhD's continuing the research.
Turn the entire moon into a cosmic ray. Full stop. THAT ought to be one helluva bigass energetic "particle".
If the baseball analogy is accurate, the impact of such a ray should cause something more than just a burst of radio waves. Why don't we see evidence of inexplicable pockmarks on the earth's surface? Or do we? 1 per km2 per centry is a lot when you have such a large surface area like the Earth. Heck, we should have reports of people being stricken down in broad daylight from time to time.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
Humanity's cross section is about 2000 km^2, so we should expect about 20 hits per year on people.
hat should help them finally tease apart the origins
How do you "tease" something apart?
...gis sdrawkcab (usually not responding to ACs; don't bother posting as AC)
I'm just wondering how long before the anti-science crowd (or the news media, in order to drum-up readership) starts presenting this as some sort of dire threat, like they did with the CERN Large Hadron Collider. That had to be stopped because it might create black holes that would eat up the entire Earth.
How will this new development be presented? "It's focusing all the cosmic rays bouncing off the moon down to the Earth; it could boil us alive!"
Whatever they come up with, I hope they work quickly though; my terror levels are starting to drop. Any lower and I might start thinking again.
Describing a baseball's speed in kilometers per hour feels like mixing systems of measurement.
You people and your slight differences disgust me! - Prof. Farnsworth
I can never tell if comments are meant in jest or not. Have you calculated the surface area of the atmosphere? Let's just take the radius of the planet and the formula for the area of a sphere.
Radius of the Earth = ~6400KM.
Surface area of the sphere = 4 * pi * 6400^2 = 514457600 square kilometers.
That's still 5 million events per year.
The earth's surface area is pretty large, but from any given point on the earth, you can only see a small bit. And it's probably cheaper to aim a detector at the moon than it is to put one in orbit and look at the earth.
While what you say is true, you fail to consider the number of protons in a baseball.
You're looking for quotes? See my journal.
Oh? and what sport in international competition do you have where it is common for a projectile to leave the playing area and randomly destroy property (break a window)? Futbol? Fiddles n sticks n chips?
I suppose you could use hail (weather), but then us filthy USAians might compare that to baseball as well: "The hail was huge!", "The size of golfballs?", "No, bigger! The size of baseballs!"
TL;DR: You complain for bullshit reasons but don't offer a better comparison which would resolve those concerns and certainly not without bringing up additional ones.
You lose at the internets.
Fine a baseball thrown by a varsity high school player.
You're an idiot commenting about a subject you know nothing about.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
Yeah they are the transport layer for God's root shell of the universe. We know that God has a shell of some kind, as he created the world by his WORD.
Cricket
This seems not very much. How do we know of them at all?
Because there are a lot of square kilometers out there... especially when the blurb doesn't actually define what the surface area of observation is!
These are what's left of lasers fired during inter-stellar wars long ago in galaxies far away that missed their targets and so are flying through space until they hit something. They lose a bit of energy in the many light year flight, but still detectable.
It's about the detection area. You can't pave the earth with detectors (half) the surface area of the moon. Or well - maybe you can but that would cost a lot more than a single indirect detector using the moons surface.
"we are all atheists about most of the gods that societies have ever believed in. Some of us just go one god further."
We know. But we're not looking for a ray here, we're looking for the shower of particles that comes when a ray hits the upper atmosphere. Is it that hard to understand?
Fine a baseball thrown by a varsity high school player
Is that a European school or a South African school?
(well, somebody had to ask!)
https://app.box.com/WitthoftResume Code: https://github.com/cellocgw
Most of an air shower will land in an area a kilometer or two wide, not fill up a huge part of the Earth's surface. Additionally, just measuring the parts of a shower at one small point won't give much info on how big the shower was (did you see one out of a hundred shower particles, or one out of a thousand particles?). To get good information you need a large number of detector elements spread out over a large area, like the Auger Observatory which 1600 water tanks spread out over 3000 km^2 (which is less than they wanted originally, due to budget limitations), plus two dozen telescopes that watch for light flashes from the showers in the sky. That is a major project, yet still has a detection area 1/6000th of the visible surface of the moon.
Current-generation cosmic-ray observatories, like the Pierre Auger Observatory and the Telescope Array, instrument a few thousand square kilometres of land area, which effectively defines the size of their detector. That gives them of the order of ten ultra-high-energy cosmic rays per year.
The moon's a lot bigger than that, so it should be able to detect more of them - or, equivalently, detect the same number of cosmic rays at an even higher energy. (They get rarer as you look at higher energies, but more scientifically interesting.)
And it's probably cheaper to aim a detector at the moon than it is to put one in orbit and look at the earth.
In this case, the detector on the ground (the Square Kilometre Array, a radio telescope) is being built anyway - so we're just planning to use it part-time. (Disclaimer: I'm one of the people involved with the project.)
Putting a detector in orbit to look down at the earth has been proposed too, though. There's the JEM-EUSO proposal, for an ultraviolet detector mounted on the international space station; and the SWORD proposal, for a free-orbiting radio detector. There are pros and cons to using different bands (ultraviolet, radio) to detect the particle cascades started by cosmic rays.
There's even a proposal to use Jupiter as the detector volume, which is even bigger. Jupiter's a long, long way away, so we'd need an unreasonably-high-energy cosmic ray to be detectable from that distance. (Rather than baseball, think artillery shell.) But it's worth keeping in mind as an auxiliary instrument on a future probe to Jupiter.
Yes, plenty of cosmic rays were detected at Mount Evans! They weren't the ultra-rare high-energy ones, but they were critical in understanding the decays of mesons produced by cosmic ray interactions. Using data from Mount Evans, Bruno Rossi showed that the more energetic mesons took longer to decay, which confirmed one of the key predictions of the theory of relativity.
My first question when I saw this was how much time on the sky you'll get.
Is a few hundred hours/year statistically significant.
Are you likely to get much more than that considering all the competing survey proposals ?
Put the new telescope in one of the stable earth-moon lagrange points so that the moon will always be visible. The one on the other side would even be quieter! That will be $0.02, please. Zaza
For the baseline case in the linked article, we assumed 1000 hours total, with the complete SKA telescope. That would be enough to exceed the exposure of all existing cosmic ray detectors, and to identify a nearby ultra-high-energy cosmic-ray source, in a mildly-optimistic scenario. For example, if Centaurus A is a source, as hinted by current data, we should be able to confirm it.
There are significant uncertainties remaining in our sensitivity calculations, though, which is largely why we plan to do some preliminary observations with the partial (Phase 1 of the) SKA. That would be enough to detect a handful of cosmic rays - maybe not enough to do real science with them, but enough to confirm that this technique works, and to find out if it's more or less sensitive than we expect.
What would be really cool, in the long run, is if we could run a second beamformer in parallel on the back end of the instrument. That would allow us to operate commensally: observing the moon whenever it's up, simultaneously with whatever other survey it's running at the time. We may have to wait a few more iterations of Moore's law before that becomes practical, though.
Can too.
StoneCypher is Full of BS
So an astronaut could be just working away in space and suddenly Booof! they are gob-smacked by one of these and lose an eye?
I suppose a pebble-sized meteor out of nowhere is also a danger to them.
Table-ized A.I.
Chrome the Moon?
We detect the particle spray that they start when they hit the upper atmosphere.
Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
What about a network of indirect detectors across the surface of the moon. Or low lunar orbit?
While what you say is true, you fail to consider the number of protons in a baseball.
Sure, but if you don't live in a country where baseball is commonly played then it is hard to have a frame of reference for how large a baseball is. Conversely if you do live in a country where baseball is commonly played then you likely don't use the metric system in daily life.
Damn_registrars has no butt-hole. Damn_registrars has no use for a butt-hole.