The Northern Lights are among the most well-documented and well-researched phenomena occurring on our planet. A result of the collisions between gaseous particles in our atmosphere and charged particles emitted from the Sun, the dazzling light shows produced are among the most spectacular on Earth. The aurora borealis, along with aurora australis, the southern hemisphere’s equivalent, are merely two examples of atmospheric light phenomena. Other examples include the more common and obvious types, such as lightning, and less common variants such as earthquake lights. Of the more mystifying and unexplained of these phenomena are the Hessdalen lights.
Hessdalen is a valley located in the central part of Norway, some 75 miles south of the city of Trondheim. The unique phenomena occurring there come in a variety of shapes and sizes. Some are fast moving while others seem to float, gently bobbing but otherwise immobile. Local residents and other witnesses have documented occurrences during which the lights seem to possess an inner solid structure, which adds another layer to the mystery. The varying morphology of the phenomenon makes researching their cause all the more complex.
The Hessdalen Lights. Picture by B.J Hauge, 2007. Credit - Monar et al; Hessdalen: A Perfect "Natural Battery"
Much of the research into the possible causes and explanations for the Hessdalen lights comes from the work of Erling Strand and his teams. Strand and his teams were to first observe the lights themselves (they are not a rare occurrence, happening 10-20 times a year, often more) and categorise them. The lights were grouped into four categories; close-to-ground phenomena, randomly flying phenomena, micro-flashing phenomena and flying phenomena apparently showing an inner structure. The former three were regularly observed while the last has yet to be observed with any instrumentation and is much more likely to hold place amongst the Area 51/UFO type conspiracies, far better consigned to science fiction.
The scientists working alongside Strand and his teams are experts in the physics and chemistry of ionised plasmas; a fourth fundamental state of matter alongside the more common solid, liquid and gas states. Ionised plasmas are essentially atomic nuclei in a gaseous state stripped of electrons, hence becoming positively charged. Lightning and neon lights are two everyday occurrences of these ionised plasmas, and the Hessdalen lights are likely to be attributable as such.
But what is likely to cause these plasmas to occur in a remote valley in central Norway? Aside from being a picture-postcard sort of scene, the landscape is rather geographically unexciting.
Or is it? The Hessdalen valley is split in two halves, divided by the Hesja river. Any GCSE standard geography textbook will have you realise that this is commonplace, but geologically speaking, the Hessdalen valley is rather interesting. The western half of the valley contains a significant amount of iron and zinc within the rock, whereas the eastern half contains much more copper. Sulphur was historically mined on the eastern side of the valley, with a run-off from the mines pouring waste into the Hesja river. The idea here is that the valley acts, essentially, as a massive natural battery.
How does this idea of the natural battery work? It can be explained by some relatively simple chemistry. The two sides of the valley act as electrodes, where oxidation (loss of electrons) and reduction (gain of electrons) of the constituent metals occurs. Zinc and iron have a smaller affinity for electrons than copper, so there is a natural inclination, as governed by the laws of thermodynamics (I’m a merciful being, I’ll spare you the details), for electrons to cross the river into the copper. In order to keep the charge balanced across the river, ions must be present in the water. As electrons move one way, charge is lost, and so this must be balanced by the negative ions moving in the opposite direction to the electrons.
Where do these come from? The answer lies in the sulphur mines. Remember the much maligned jar sat at the back of the chemistry lab with a big orange “corrosive” sign? Sulphuric acid – yep. That’s thought to be present in the river, and the sulphate ions (SO42-) act as charge balancers, allowing for this electrochemical process to occur. But, this doesn’t quite explain why the lights are seen in the sky.
Some fancy pots and pans. An electric field meter used to probe for evidence of the "natural battery". Credit – Monar et al.; Hessdalen: A Perfect Natural Battery”
The sulphur mines are thought to be responsible for emission of gases which may become ionised (ie. charged). These ions can then be supported in water droplets present in the air, forming “bubbles” of ions in the sky. These have been reported to be seen on radar without emitting any light, but it is hypothesised that when these ionic bubbles move along the electric field lines generated by the natural battery, the voltage may cause rapid discharge within the ionic bubbles, causing the smaller, rapid flashes. This scenario is most likely to be responsible for the light emission, though it is also possible that cosmic particles from the sun (as is the case with the aurorae) may also cause these bubbles to glow. Both hypotheses are still to be tested, but it seems, as is often the case, that the mysterious isn’t unexplainable!
Monar et al, 2007, Hessdalen: A Perfect “Natural Battery” , http://www.itacomm.net/PH/2013_Monari_et-al-en.pdf