# Under what circumstances would it be possible to harvest aurora for either energy or matter?

I would like to have a planet in which somehow it becomes necessary to harvest aurora for energy (and maybe matter if that's feasible).

The civilization of this planet is moderately advanced -- enough to have colonized other planets in its solar system, but not enough to have travel between stars.

Which of the following would improve the plausibility of harvesting aurora:

• A planet smaller or bigger than the earth
• A planet with a weaker or stronger magnetic field
• A planet closer or further away than the earth
• A sun smaller or bigger than our sun
• A higher rate of solar activity
• A planet with a smaller or bigger atmosphere (or no atmosphere)
• Aurora (like the borealis kind) is just solar dust hitting the atmosphere, not much energy in that compared to using solar panels – ratchet freak Dec 5 '14 at 15:25
• @ratchetfreak But if we can get one of these, and put it next to the star... – Crabgor Dec 5 '14 at 15:30
• @rachet_freak - Not dust, but charged particles. So they could induce some current. But as you say, the energy density is very low to use as a power source. – Oldcat Dec 5 '14 at 19:44
• The energy cost of collecting ions from an aurora would be far greater than any returns. Think of driving you car 70 miles to collect the output of a fluorescent light bulb with a solar panel. – pojo-guy May 25 '17 at 3:37

Auroras are caused by charged particles, mainly electrons and protons, entering the atmosphere from above causing ionization and excitation of atmospheric constituents, and consequent optical emissions. Incident protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.

So are you trying to collect the ionization particles or the light generated from them?

Catching ionization you'll need to have some kind of satellite, I'm not sure it be worth it. You'd need something to convert the ions to energy. We already have solar tech and it is getting better all the time. As ratchet freak said, You're going to get a lot more power from solar cells.

We capture such a small amount of energy from the sun it is almost negligible. Part of the idea behind things like the Dyson sphere and rings etc. is it is build partly to capture a lot more of the suns energy to give us more power, a Dyson Swarm or Bubble would be more likely scenario. Many smaller structures orbiting the Sun all capturing energy.

• I really should have realized that if a civilization can get to anywhere in the solar system, it can build a Dyson Swarm. Thanks for the answer! – bananafacts Dec 5 '14 at 16:09
• @bananafacts Glad I could help! – bowlturner Dec 5 '14 at 16:13
• Many smaller structures orbiting the Sun all capturing energy I just pictured a Dyson Bubble consisting entirely of Star Forges when I read that. – Thebluefish Dec 5 '14 at 18:47

I don't think we could directly harness the energy transferred to particles in auroras. However, we could probably captured the energy from the phenomena that caused auroras.

Wikipedia notes that the primary cause of auroras is an interaction between the Sun and the Earth's magnetosphere. Here are some ways we could exploit that:

• The solar wind. The solar wind is the primary cause of auroras. It's a continuous ejection of particles (e.g. electrons and protons) from the outer reaches of the Sun. When these particles interact with Earth's magnetosphere, they can cause and aurora.

The obvious use of the solar wind is to propel a solar sail, and push a spacecraft across vast distances. This makes travel to distant stars possible.

However, solar sails work off of the principle of radiation pressure - the idea that photons emitted by the Sun can exert a force against an object. The particles in the solar wind can also exert a force. In this answer, I calculated the force of a stellar wind on a spacecraft, and here, I calculated the force that a laser would exert on a comet. If you could take into account the force from particles of the stellar wind, you could calculate the force they would create if they pushed against a sort of "solar windmill".

Take a long rectangular object, and put it so that the longest side is bared against the Sun. Create a magnetic field emanating from a location 1/4 of the way from one edge that diverts the charged particles, so that only half of the rectangle is exposed to the solar wind. This means that the force will exert a torque on the rectangle, causing it to rotate. You might be able to harness the rotational energy of the rectangle.

(Replace "bounce" with "solar wind"!)

• Coronal mass ejection/Solar flade. Coronal mass ejections, or CMEs, often change the intensity of the solar wind. They can have some pretty bad effects on Earth! They're also related to solar flares, which can also have some negative effects.

Both of these events are related to the emission of additional X-rays from the Sun. These X-rays are very energetic, and are also damaging to Earth. However, if the X-ray flux were high enough, a large amount of energy could be obtained from a small area. In essence, a satellite might be able to harness a lot of solar power - if it was properly equipped to handle it!

• Exactly. You can capture solar wind in space and use it for solar sail of something, but once wind is in the Earth's magnetosphere it is over - it is just too weak to bother. – Peter M. - stands for Monica Dec 5 '14 at 18:19