On Saturday the 18th of April there was an Open Campus day at Riken Wako. It was estimated that about 5 000 people visited the campus that day to learn more about science, research and the Riken Wako Campus. For us this luckily didn’t mean we had to clean the office. That would be a full time job for a couple of people for a long time. However, it did demand we each put together a quick presentation about our work and what we’re doing.

Since I’m now part of the JEM-EUSO collaboration and being Swedish I thought I would do a nice twist on the presentation. I was also told that the majority of the audience would be children. Given the popularity of the Marvel films I thought I could talk about the Norse God Thor.

Thor was the Viking God of Thunder and Lightning. He had a hammer which produced the lightning and when riding across the sky in his chariot it caused the rolling thunder.
(Copyright Marvel and all that stuff)

However, today we know that this might not really be the case. In 1749 Benjamin Frankling performed his experiment with the key tied to the string of a kite and in doing so proved that the lightning actually was electricity. Today we have quite a good grasp of how the actual lightning bolt works but there are, to many peoples surprise, still some mysteries regarding lightning. The main mystery is the we actually still have no confirmed understanding of how lightning actually can be created. Here’s some more physics…

In order for lightning, or a static discharge to occur the potential difference between two opposite charged objects have to exceed a certain threshold. If the electric field is higher a discharge can occur. This is exactly what happens when you reach for the door handle and just before you can grab it there’s a spark and your finger hurts. In order for this discharge to happen the electric field in air has to be higher than about 2 MV/m (Mega Volt per meter, i.e. 2 000 000 V/m). This implies that if the discharge occurring when you reach for the door handle happens when your fingertip is about 1 cm from it the lightning bolt will measure about 20 000 V.

Here’s the strange part, measurements which have been performed in thunder clouds show that the electric field is not even near being strong enough to support the lightning discharge that actually occurs.

One theory has been put forward which could explain the lightning even though the lack of electric field strength. The theory is referred to as the Runaway Breakdown, and is an effect of cosmic radiation hitting the atmosphere and creating an Air Shower (see earlier post).
The classical depiction of an air shower from an arriving cosmic ray

Studies of this phenomenon have so far not been able to disprove a connection between lightning strikes and the arrival of cosmic rays. In fact the results show rather the opposite, that there most likely is a connection between the two phenomena.

The JEM-EUSO collaboration will be studying this by observing lightning from the International Space Station and compare the lightning strikes with the detection of arriving cosmic rays.

So the JEM-EUSO collaboration will be able to answer the question if…

Thor was the God of lightning and thunder

or in fact

the god of cosmic rays…