Opinions on Jupiter's evolution have undergone a revision, following the data sent by the Galileo probe. Previous measurements had suggested that Jupiter contained about 10 times more oxygen than the sun. The old theory says that young Jupiter, bombarded by comets containing carbon, nitrogen and oxygen, became much richer in these elements (New Scientist, January 27, 1996).

Galileo's photographs, however, reveal that the oxygen content in the Jovian atmosphere is roughly the same as that of the sun's. Tobias Owen of the University of Hawaii says that settling in of the original dust particles in Jupiter's atmosphere is a more feasible explanation for its present state than later cometary impacts.