Figure 36.21 Processes contributing to Jupiter's atmospheric composition.
Jupiter's strong gravity trapped a sample of all the ingredients in the solar nebula from which the Sun and planets formed 4.5 billion years ago. From Jupiter's size and mass, astronomers have long known that it is made almost entirely of hydrogen and helium, the two most abundant elements in the Sun and in the universe as a whole. Planetesimals formed from the solar nebula and became the building blocks of the planets. Collisions between these icy planetesimals are believed to have produced a large icy core onto which hydrogen and helium gas was trapped to form Jupiter. Planetesimals remaining after the formation of the planets have bombarded Jupiter (as well as the other planets) during the past 4.5 billion years. These small bodies have enriched the mainly hydrogen and helium gas of Jupiter's atmosphere with heavier elements--mainly carbon (in the form of methane, CH4), nitrogen (in the form of ammonia, NH3), oxygen (in the form of water, H2O), and sulfur (in the form of hydrogen sulfide, H2S). By determining the abundances of these gases, additional information can be obtained about the planetary formation process and the role of impacts in planetary evolution. (NASA/Ames)
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