A low-temperature origin for the planetesimals that formed Jupiter

The four giant planets in the Solar System have abundances of 'metals' (ele ments heavier than helium), relative to hydrogen, that are much higher than observed in the Sun. In order to explain this, all models for the formatio n of these planets rely on an influx of solid planetesimals(17). It is gene rally assumed that these planetesimals were similar, if not identical, to t he comets from the Oort cloud that we see today. Comets that formed in the region of the giant planets should not have contained much neon, argon and nitrogen, because the temperatures were too high for these volatile gases t o be trapped effectively in ice. This means that the abundances of those el ements on the giant planets should be approximately solar. Here we show tha t argon, krypton and xenon in Jupiter's atmosphere are enriched to the same extent as the other heavy elements, which suggests that the planetesimals carrying these elements must have formed at temperatures lower than predict ed by present models of giant-planet formation.