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Titolo	Iron regulation
Autore	J. Himmelfarb
Referenza	J Am Soc Nephrol 2007;
Contenuto	Why does the planet Mars glow red in the night sky? The answer, of course, has to do with iron. In the early solar system, stellar energy originated from the fusion of two light nuclei that combined to make a heavier nucleus in a thermonuclear reaction. Hans Bethe was awarded the 1967 Nobel Prize in physics for describing nucleosynthesis, the mechanism by which fusion of four hydrogen nuclei makes a helium-4 nucleus, accounting for the bulk of energy that is produced by the sun. However, the nucleosynthetic process does not end with helium, because larger nuclei also can be fused in brilliant stars to make heavier elements. In a classic paper of 1957, Hoyle et al. described a wide range of nuclear processes that are important in synthesizing the chemical elements during stellar evolution (1). Of importance, the end of the nuclear burning chain is marked by the formation of elemental iron, which has a particularly stable nuclear structure. Because the synthesis by nuclear fusion of elements that are heavier than iron actually costs rather than liberates energy, by the time a star has synthesized a core of iron, it is doomed.
Data	14.03.2007

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