 As well as these molecules , emission from heavy atoms such as iron , magnesium and silicon was detected , with abundances consistent with what would be found in a cometary nucleus . Although a substantial amount of water was detected spectroscopically , it was not as much as predicted beforehand , meaning that either the water layer thought to exist below the clouds was thinner than predicted , or that the cometary fragments did not penetrate deeply enough . The relatively low levels of water were later confirmed by Galileo 's atmospheric probe , which explored Jupiter 's atmosphere directly . 
