Antiproton ring found around Earth | Hacker News Reader

Antiproton ring found around Earth

newscientist.com

46 pointsColinWright15 comments

Presumably there are antimatter rings around Jupiter and the other gas giants as well.

I think the interesting new things to know are 'don't let you satellite pass through an anti-proton belt' and when cosmic rays create anti-matter it doesn't all get instantly annihilated.

But it raises some other interesting questions, since we've seen that lightning can create anti-matter as well [1] one has to wonder why their aren't actual pools of anti-hydrogen around planets. Clearly the annihilation rate is going to eat some of it, but if some can accumulate, the planets been here a long time, where is the rest?

[1] http://science.nasa.gov/science-news/science-at-nasa/2011/11...

Isn't "billions" of anti protons an absurdly small number to talk about spaceflight fuel. Per http://www.answerbag.com/q_view/154104 (which looks about right) we have 2.73 X 10^26 hydrogen atoms per pound.

An antiproton is basically an antihydrogen missing its positron.

Yeah. This might be good for scientific experiments with anti-matter though.

Annihilating all of it would result in about 1 tenth of a joule.

One antiproton annihilation will give you about 1 GeV. Annihilate a billion of them, and you've got 10^18 eV. One eV is about 10^(-19) Joules. So, yeah. A tenth of a Joule. Underwhelming.

And the larger planets might have 27 kilowatt hours worth! Hopefully something was lost in translation of this article from scientists to journalists.

Here are a couple of things:

• If it only persists for minutes, that's a tenth of a joule per few minutes, if you have some way to capture and confine it away from the corrupting influence of matter. That sounds a little bit more practical than a tenth of a joule, total.

• The big deal with antimatter is that it has a high energy density. Even if you have a very small amount of it, it still has a high energy density. A hundred joules can accelerate a one-milligram spacecraft to 5000 meters per second, which is almost enough to stay in low earth orbit. 10 kJ can accelerate a one-microgram spacecraft to 1.6 million m/s, or 0.5% of the speed of light. And 10kJ of matter/antimatter reaction works out to 5.6 × 10⁻¹⁴ g, so it's easy to imagine containing that much in a one-microgram spacecraft. If you can gather a tenth of a joule of antimatter per hour, you only need 11 years to gather enough antimatter to launch your one-microgram probe toward Alpha Centauri.

It looks like there's a word missing in the quote:

"We are talking about of billions of particles,"

Even if the missing word is another "billions", that still seems rather low.

Yeah, I hope it's a "journalist not understanding large numbers" error. It would be fantastic to have tons of anitmatter in harnessable range like that.

OK, so the New Scientist article is based on

   THE DISCOVERY OF GEOMAGNETICALLY 
   TRAPPED COSMIC-RAY ANTIPROTONS
   Astro. J. Letters 737:L29, 2011 August 20
   DOI: 10.1088/2041-8205/737/2/l29
   http://iopscience.iop.org/2041-8205/737/2/L29/

The key sentence from that abstract is

"PAMELA data show that the magnetospheric antiproton ﬂux in the SAA exceeds the cosmic-ray antiproton ﬂux by three orders of magnitude at the present solar minimum, and exceeds the sub-cutoff antiproton ﬂux outside radiation belts by four orders of magnitude, constituting the most abundant source of antiprotons near the Earth."

The cosmic ray flux is estimated in another paper on the PAMELA results:

   "PAMELA Results on the Cosmic-Ray 
   Antiproton Flux from 60 MeV to 180 
   GeV in Kinetic Energy"
   Physical Review Letters 105, 121101 (2010)
   DOI:	10.1103/PhysRevLett.105.121101
   http://prl.aps.org/abstract/PRL/v105/i12/e121101

After eyeballing Fig. 1, I'd say they measured most antiprotons to be between 1 GeV and 10 GeV, with a flux of ~2x10^-2 / (GeV m^2 s sr). (sr=steradians.) The flux peaks around 2 GeV.

Rough multiplication gives an estimate of total flux:

   [2x10^-2 / (GeV m^2 s sr)]*[9 GeV]*[10^14 m^2]*[4 pi sr] 
     = 2*10^14  antiprotons/second.

If we ignore the kinetic energy of the antiprotons, and assume there are plenty of available protons to annihilate with them, we get about 2 GeV per antiproton. This yields

   [2*10^14  antiprotons/second]*[2 GeV/anitproton]
       =  6x10^ 4  J/s

The space shuttle orbiter weighs 69,000 kg empty. The escapte velocity from earth (which doesn't change much between the surface and the edge of the atmosphere) is 11.2 km/s, so the minimum energy needed to get it out of the earth's atmosphere is

   [1/2]*[69,000 kg]*[11.2 km/s]^2
      = 4x10^12 J

OK, so it would take about 10^8 s, or 3 years, to collect enough energy from antiproton cosmic-ray rest mass to lauch a space-shuttle size object out of Earth's gravity. And you'd have to scoop up from the entire surface area above the earth.

Now, the magnetospheric antiproton flux in the South Atlantic Anomaly

    http://en.wikipedia.org/wiki/South_Atlantic_Anomaly

is said to be 3 orders of magnitude larger than the normal antiproton cosmic ray flux. By looking at the wikipedia page, it looks like the SAA covers about 10% of the surface area above the earth. If we were able to scoop up all of the antiprotons in the magnetospheric belt, it would then take about 10^6 s, or 11 days, to get enough energy to launch a space-shuttle sized object.

I am highly, highly unsure about these number and the assumptions that went into them, but it at least suggests it's possible to do. Lemme know if I did something stupid.

Thanks for all the work, even if you did make a math error, I appreciate your look over of the raw time to launch required for what you're talking about.

This is tomorrow's oil.

Not likely. The special thing about antimatter is its spectacularly high energy density, not its abundance and easy extraction. Solar energy is tomorrow's oil.

It's not likely that solar is tomorrow's oil for two reasons; 1) it won't provide orders of magnitude more energy as oil did when it was discovered and, 2) it is not a finite resource. Solar/wind/green whatever will merely allow us to prevent a grind to a halt.

Yes, solar will provide orders of magnitude more energy, the way oil did. This is one of the most important facts in 21st-century politics and economics, so it's surprising that it's so little-known.

Total world marketed energy consumption is about 500 quadrillion Btu per year, about 17 terawatts. Total terrestrial insolation is about 130 000 terawatts. That's almost four orders of magnitude more. It's just that, until now, it's been more expensive than fossil fuel to extract it, with low EROEI and long payback times. That has changed in the last decade, but really only in the last four or five years.

It is true that it is not a particularly limited resource; the sun will continue burning for a long time, regardless of whether we set up solar panels or not.

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