The 340 kg Galileo entry probe entered the atmosphere of Jupiter on December 7, 1995 at a speed of 170,000 km hr-1 and a shallow entry angle as shown in Figure 7.41. The probe was "aero-captured" by Jupiter's atmosphere (experiencing a maximum deceleration of 230g), and once it had slowed sufficiently, its heat shield was jettisoned, a parachute deployed, and the probe then descended slowly down through the atmosphere recording information with several instruments on the way. Instruments included a particle nephelometer (Ragent et al., 1998), a mass-spectrometer (Niemann et al., 1998), a net flux radiometer (Sromovsky et al., 1998), and a host of thermometers and accelerometers to record vertical structure (Seiff et al., 1998). In addition to the in situ observations, the probe signal was also tracked from the orbiter and the Doppler-shifting of the signal used to deduce horizontal wind speeds down to depths of nearly 20 bar, while the strength of the signal was used to determine the deep NH3 abundance.
The probe collected data for 58 minutes as it descended through Jupiter's atmosphere, with the transmission terminating at a pressure level of ~20 bar (Young, 2003). The findings of the probe have already been discussed in Chapters 4 and 5 and the probe data provide the only "ground truth'' we have for conditions in the Jovian atmosphere. However, as discussed previously, it was somewhat unfortunate that the probe entered the atmosphere in a rather unrepresentative 5 ^m hotspot region and it
would be highly desirable to fly further multiple probe missions to explore other more typical regions.
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