Prior to the Voyager missions and in the presence of only the photographs
or the drawings by different authors, the observing results of 1973
mutual events have been much useful to define the physical parameters
and the surface morphology of Jupiter and Saturn's satellites. As an
example, the comparison between the albedo of eclipsed areas and
the loss of light in different colors inferred the existence of bright
polar caps, suggested by the drawings (Blanco and Catalano 1974).
Since the Voyager missions have provided accurate radii for all the
satellites and described surface features and albedo variations, the
observations of mutual events were best used for astrometric
purposes. The relative separations in right ascension,
cos
, and declination,
, of a satellite pair at midevent were estimated.
The improvement of the integration time up to measures of the order of
0.1 sec, can supply relative positions with relevant residuals near 100
Km at Jupiter's mean distance and near 800 Km in longitude and about
half in latitude at Saturn's distance (Aksnes et al. 1984).
But after the 1980 campaign the observing conditions were completely
changing by the coming of the receptors. Their resolution, of the
order of arcsec per pixel, by the analysis of the lightcurve behavior
during the event, also with small telescopes, makes it possible to
obtain morphological details of the order of few kilometers. The use
of several infrared wavelengths during Io's occultations by the other
satellites, allows the detection of emitting hot spots associated
to an intense volcanism on the first Galilean satellite of Jupiter
(Arlot 1988).
The last part of the analysis is devoted to mutual events between
Pluto and Charon, the only two bodies of the Solar System that
have not been visited by a spacecraft yet. Together with the rare and
sporadic stars occultations, mutual events represented the
best opportunity to learn a great deal about this particular planetary
system, especially to define the surface morphological characteristics
of the two bodies. Useful suggestions of Pluto's redder color
with respect to Charon's bluer (less red) color came from the
different behavior of observed B and V lightcurves.