Helium

Helium is a colorless, odorless, tasteless, non-toxic, nearly inert monatomic chemical element that heads the noble gas series. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions. Extreme conditions are also needed to create the small handful of helium compounds, which are all unstable at standard temperature and pressure. Its most abundant stable isotope is helium-4 and it has a rare stable isotope, helium-3. The behavior of liquid helium-4's two different states -helium I and helium II - is important to researchers studying quantum mechanics (in particular the phenomenon of superfluidity) and those looking at the effects that near absolute zero temperatures have on matter (such as superconductivity).

Helium is the second most abundant and second lightest element. In the modern Universe almost all new helium is created as a result of the nuclear fusion of hydrogen in stars. In planetary environments it is created by the radioactive decay of much heavier elements (alpha particles are helium-4 nuclei produced by alpha decay). After its creation, part of it is trapped with natural gas in concentrations up to 7% by volume. It is extracted from the natural gas by a low temperature separation process called fractional distillation.