Final answer:
The deepest layer that the Galileo spacecraft's probe was able to directly sample in Jupiter's atmosphere was the gaseous and liquid hydrogen layer, not reaching the metallic hydrogen layer or the rocky core.
Step-by-step explanation:
The Galileo spacecraft's probe was designed to sample Jupiter's atmosphere by descending into it after being launched in 1989 and arriving in 1995. The probe survived for about an hour, descending to a depth of 200 kilometers, which is approximately 0.3% of Jupiter's radius. This depth would place the probe within Jupiter's upper atmospheric layers, which consist predominantly of gaseous and liquid hydrogen, as well as helium and traces of other gases.
The probe was not able to sample the metallic hydrogen layer or the rocky core, which lie at much greater depths. As it descended, it was expected to pass through a region of frozen water clouds and then into a lower layer of clouds of liquid water droplets; however, it found none of these, descending through a dryer and clearer part of the atmosphere it termed the "desert" of Jupiter, eventually making its measurements up to a pressure of 22 bars before ceasing to function and vaporizing.