The Galilean satellites range in maximum angular diameter from for Europa to for Ganymede, and Titan's diameter never exceeds . These objects occupy in central position in planetary science, exhibiting a wide range of interesting physical phenomena from hot spots with volcanos on Io to a complex atmosphere more dense than Earth's on Titan. Disk averaged brightness temperatures of these objects have been measured with the VLA and Titan has been extensively studied with the VLA/Goldstone radar configuration, again with essentially full-disk averaging. The enhanced VLA will significantly advance the study of these objects in two important ways. Io and Europa's orbits are very close the surface of Jupiter and confusion from the planet severely affects the measurements of the satellites' disk temperatures as a function of their orbital longitudes. Jupiter's confusing flux density can be minimized by greatly increasing the continuum bandwidth of the VLA. Continuum observations of Io at 7mm and 1.3cm should then reveal the variations in mean surface brightness caused by the changes in the viewing geometry as Io orbits Jupiter. The hot spots have been observed only in the IR which is sensitive to the very surface. Measurements at 7mm and 1.3cm will probe the hot spots to depths of roughly 10 wavelengths. The subsurface probing is important for all of the satellites. The improvement in sensitivity at 1.3cm as well as full capability in the 40-50 GHz band are very important for these measurements.
Clearly, the Galilean satellites and Titan are over resolved with the VLBA. However, the A+ configuration is ideally matched to these targets, both for thermal continuum emission at short wavelengths and bistatic radar at 8.4 GHz. If the aperture of that array was weighted to about 100 km, the satellites would be resolved to about 10 beams on a diameter and meaningful maps would be produced. The full A+ configuration could be used with great profit for bistatic radar in the 2.4 GHz band. The radar experiments are necessarily narrow-band and confusion from Jupiter is again a problem for studies of Io.