the lighter noble gases—approximate prices for the purchase of small quantities in Europe in 1999 were 10 €/L (=~€1.7/g) for xenon, 1 €/L (=~€0.27/g) for krypton, and 0.20 €/L (=~€0.22/g) for neon, while the much more plentiful argon, which makes up over 1% by volume of earth's atmosphere, costs less than a cent per liter. Solar system Within the Solar System, the nucleon fraction of xenon is , for an abundance of approximately one part in 630 thousand of the total mass. Xenon is relatively rare in the Sun's atmosphere, on Earth, and in asteroids and comets. The abundance of xenon in the atmosphere of planet Jupiter is unusually high, about 2.6 times that of the Sun. This abundance remains unexplained, but may have been caused by an early and rapid buildup of planetesimals—small, subplanetary bodies—before the heating of the presolar disk. (Otherwise, xenon would not have been trapped in the planetesimal ices.) The problem of the low terrestrial xenon may be explained by covalent bonding of xenon to oxygen within quartz, reducing the outgassing of xenon into the atmosphere. Stellar Unlike the lower-mass noble gases, the normal stellar nucleosynthesis process inside a star does not form xenon. Elements more massive than iron-56 consume energy through fusion, and the synthesis of xenon represents no energy gain for a star. Instead, xenon is formed during supernova explosions, in classical nova explosions, by the slow neutron-capture process (s-process) in red giant stars that have exhausted their core hydrogen and entered the asymptotic giant branch, and from radioactive decay, for example by beta decay of extinct iodine-129 and spontaneous fission of thorium, uranium, and plutonium. Nuclear fission Xenon-135 is a notable neutron poison with a high fission product yield. As it is relatively short lived, it decays at the same rate it is produced during steady operation of a nuclear reactor. However, if power is reduced or the reactor is scramed, less xenon is destroyed than is produced from the beta decay of its parent nuclides. This phenomenon called xenon poisoning can cause significant problems in restarting a reactor after a scram or increasing power after it had been reduced and it was one of several contributing factors in the Chernobyl nuclear accident. Stable or extremely long lived isotopes of xenon are also produced in appreciable quantities in nuclear fission. Xenon-136 is produced when xenon-135 undergoes neutron capture before it can decay. The