aluminum

Aluminum (or aluminium, Al) is the element with atomic number 13, symbol Al. Virtually all of it is of one stable isotope, with mass number 27, other isotopes being radioactive with none lasting more than an hour except ²⁶Al, which has a half-life of 717240 years. By one determination, aluminum is the thirteenth most common element by mass. Among the places aluminum is detected are stars, the interstellar medium, and clouds, such as planetary nebulae. Its nucleosynthesis is presumed to occur in post-main-sequence stars and supernovae, but its production remains a subject of interest, in particular, the production of observed radioactive ²⁶Al, with its limited lifetime. Given observed amounts, such radioactive aluminum could be a significant source of heat in the early life of some extra-solar planets.