Space is indeed the final frontier. It contains everything that we could possibly investigate as scientists, and then some. The challenge of space lies in direct proportion to the scales of existence. As astronomers, we gaze out at things so incredibly vast that we simply cannot fully appreciate the extent of what it is we are exploring. The miniature world is equally jaw-dropping, though much harder to look at. The secret realm of particles shows as little sign of a terminating spatial limit as the bigger span of the cosmos, and somewhere in between those two daunting extremes, we stand and observe.

If we have serious difficulty resolving the face of distant galaxies, those gargantuan creatures hundreds of thousands of light years across, how much more difficult is it then to get a clear signal from the tiny things that swarm through the caverns of deep space? In my background account of fundamental astrophysics, The Virtue of Heresy, I coined a term for this conundrum: The Spatial Credibility Factor. It describes the difficulties of scale, implying that the more remote something is from point of observation, the less we ought to claim to know about it, with the corollary that our explanations of remote objects tend to become ever more improbably fantastic the further removed the subject finds itself. Examples of the Spatial Credibility Factor at work at either extreme are the recently lauded Higgs boson, and the ongoing controversy surrounding quasars.

For all these reasons (and more, no doubt), deep space becomes a happy hunting ground for theorists bursting to inflict their imaginations upon our sensibilities. Some theoretical descriptions are indecipherably vague, others challenge our intuition, and all are practically impossible to test. One such notion is the characterisation of space as a vacuum. Before we can attempt to explain the misconceptions around electric currents in space, we must ask ourselves, is it really a vacuum? It is a question that necessarily requires an understanding of what a vacuum actually is.

A vacuum in the parlance of physics is an empty physical space, a complete absence of matter. It is a volume with no mass at the time of measurement, and thus has zero density and pressure. Because of the relatively high speeds of ubiquitous interstellar particles, one would expect that in reality, any given volume would fluctuate rapidly in density as quanta passed through it, and that hints at what a vacuum actually is: A theoretical ideal, never realised in practice. The distinction between matter and energy is blurred, though they are measurably equivalent. It may be that it is simply a case of phase transition, as seen, for example, when water undergoes changes with increasing temperature from ice to liquid to vapour. Quantum Mechanics takes the idea a step further, positing that space itself has texture and uniform latent energy, although that has not been empirically verified. Be that as it may, it is nevertheless fair argument to say that the presence of energy in a given volume denies it the opportunity of being called a true vacuum.

The preamble leading us into this essay is necessary, for the simple reason that the wording of this misconception carries the questionable assumption that space is a vacuum. Notwithstanding that caveat, let us now turn our attention to the phenomenon of electricity in interstellar space, and whether it is physically viable or not.

Electricity is defined in physics as “The physical phenomena arising from the behaviour of electrons and protons that is caused by the attraction of particles with opposite charges and the repulsion of particles with the same charge.” The charge associated with electric current is carried by electrons, and is designated negative by convention. An electric charge produces around itself an electric field, the means by which it transmits force to other nearby charges. It does this even when it is not moving, and when the charge does move, it creates in addition to the transmission of force, a magnetic field. Ergo, an electric current is a continuous stream of negatively-charged electrons in a magnetic field.

The question being asked is whether electrical currents can flow in interstellar space, but before we address that, we should enquire whether there are sufficient free electrons to constitute electric currents in space in the first place. There certainly are, in stupendous, incalculably large numbers. An electron is conceptually a fundamental particle, one of three species that make up the structure of atoms according to the standard Bohr model, the other two being protons and neutrons. Positively charged protons and chargeless neutrons make up the nuclei of most atoms, and these are counterbalanced by an equal number of negative charges in the form of electrons orbiting in shells about the nucleus[1]. Thus, in their native state, atoms are electrically neutral.

The process by which atoms achieve charge status is called ionisation, something that is seen to occur in the laboratory and throughout space. Atomic charge is brought about by the subtraction or addition of electrons. Ionisation happens quite naturally in various ways, principally by photo-ionisation and collisions. In order to avoid over-complicating this discussion, we won’t include the creation of negative ions by electron absorption, which also occurs freely in space. We shall also stay away from the quantum mechanical theory of ionisation because it is conceptually and logically troublesome.

The most abundant atom in the observed universe is hydrogen. It is also the simplest and least complex of all the elements. In its neutral state, a hydrogen atom consists of just a single, lone proton in the nucleus, with one electron in orbit about it. Hydrogen is seen and measured in vast clouds throughout the cosmos, and most appreciably in the surface layer of stars like the Sun and in the solar atmosphere. There, in the Sun’s powerful and extensive magnetic field, a sea of electromagnetically bound protons and electrons is bathed in light. The photon energy being absorbed by the atom excites the electron, to the extent that its internal energy passes a binding threshold, and the electron is freed from the parent proton. The same scenario occurs in collisions between atoms and other particles, with the net result that the solar atmosphere is suffused with positively charged free protons, negatively charged free electrons, and of course, magnetism.  Every high school physics student knows what happens next!

Charged particles in a magnetic field do one thing consistently: They accelerate. They get moving at high speed, and consequently the solar atmosphere is at particle level like an angry swarm of bees. It is a gas undergoing Brownian motion[2]. There is a further consideration that needs to be brought in here: When a gas is exposed to heat and an electric field, it goes through phase transition to the fourth state of matter (after solid, liquid, and gas)—plasma. Because those conditions appear to exist around every incandescent star (and certainly around the Sun), it’s easy to see why plasma is the most common form of matter in the cosmos. Plasma physics is huge field of study with an extensive volume of literature, so we should only skim it here. Suffice to say that plasma is suffused with charge carriers, and that makes it an electrically conductive medium that is highly responsive to electric fields.

Where a voltage differential exists in an electric field, there is a tendency, or at least a potential, for electricity to arc across the gap. One of the most spectacular examples of this plasma effect is seen in lightning. Equally spectacular but less easily seen are the polar auroras. Shimmering polar lights, like lightning, are clearly seen and photographed on other planets in our Solar System, and this is because they are all caused by the same underlying conditions, which pervade the entire system. The auroras answer the question posed by this misconception in the most beautiful way. Between the Earth and the Sun, there is a veritable flood of charged particles, called the solar wind.

Auroras are a direct consequence of the solar wind, a flow of unbound electrons and protons (that is, plasma) accelerated outward from the Sun. The Earth’s magnetic field traps these ions, mostly electrons, and guides them towards the magnetic poles. Along the way, ions collide with atoms in the atmosphere, releasing visible energy in the form of auroras in large, shimmering circles around the poles. Crucially, auroras are more frequent and brighter when the Sun’s activity is most intense. This causes coronal mass ejections that stimulate the solar wind, and provide direct correlation between electrical phenomena on widely separated celestial bodies.

Auroras are clear evidence that electric currents are not only possible in space, but actually thrive there. There is a direct electrical connection between the Sun and the Earth in the flow of electrons in the solar wind, and when that circuit is closed, voila! The lights come on. Quod erat demonstrandum.

 

[1] In 2001, University of Missouri nuclear chemist Oliver Manual showed with the atomic spectrometer in his laboratory that neutrons in fact repel one another, indicating that they do indeed carry charge. However, the science of neutron repulsion is nascent and not yet mature, so we stick for the time being with the standard view that neutrons are electrically neutral.

[2] Brownian motion or pedesis is the apparently random motion of particles suspended in a fluid.

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