Most races discover solium quite by accident, so much so that the credit for such discovery is almost always posthumous. Flat surfaces facing a system's primary at a certain distance will develop a glaze of highly unstable subatomic particles, essentially a solid mass of photons. This substance is so unstable that it frequently explodes with little or no trigger. Only by bonding it with neutral carbon can the substance be stabilized to the point that it is useful as a power source. The percentage of solium to carbon is expressed as a number, solium 20 is 20% solium and 80% carbon, for example. An engine core made of this substance is capable of driving a ship at a percentage of light speed equal to the percentage of solium to carbon. Any concentration of solium of more than 40% begins to become unstable and may begin to break down or "cook off." Adjustable rods of pure neutral carbon are incorporated into solium engine cores to allow the process to be controlled.
Most civilian vessels are only allowed to operate with solium 10 and 20 cores. Certain classes of sport vessels may be licensed to utilize solium 30 or 40 engine cores and some illegal use of the more powerful cores has been known. For this reason, traffic in solium is generally very well monitored. Normally it is only government and military vessels that use anything more powerful than solium 20. Some interceptors and deep-space probes will use cores as powerful as solium 60 but these are rare because of possible instabilities.
Solium occasionally becomes unstable despite all the controls placed upon it. This is most likely in the instances of damage to the ship's engine compartment. In the event of such a "core breach," control rods may be inserted or "scrammed" to halt the reaction. After a cool-down period, the rods may be removed and the core reinitialized to run the ship. In extreme cases, if scramming the core does not halt the reaction, it may only slow down the process, in effect delaying detonation of the core until it can be jettisoned or "dropped" and allowed to thrust to a safe distance.
