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Photography of Jupiter 
On December 4, 1973, after a flight of 21 months including pas- 
sage through the Asteroid belt, Pioneer 10 passed by Jupiter at a 
distance of 130,000 km (35). A year later on identical spacecraft, 
Pioneer 11 approached within 42,000 km of the planet. Among a 
variety of other experiments, both spacecraft carried an Imaging 
Polarimeter to measure brightness, color, and polarization of light 
reflected from the planet at phases not visible from Earth (36), 
Similar measurements were made of the asteroids, Jupiter's large 
satellites, and the dust cloud surrounding the Sun which is seen 
from the Earth as the zodiacal light. The instrument contains a 
25 mm Maksutov-type telescope that focuses light within the visible 
spectrum onto a multi-element motor-driven aperture assembly. 
Selectable field-defining apertures, a depolarizer, a retardation 
plate, and a radioisotope-activated calibration source mounted on 
the aperture assembly analyzed the light before it was recorded in two 
spectral bands. The telescope can be aimed fore and aft with respect 
to the spacecraft trajectory. As the field of view is swept 360° 
about the spacecraft spin axis, it described conical scans on the 
planetary surface. Ten two-color pictures were taken in the 20 
hours surrounding closest approach. Digitally reconstructed with 
noise removed and color composited, these pictures give a remarkable 
view of the giant planet with the shadow of its moon Io crossing the 
face. Digital processing of other pictures of the moon Ganymede 
indicate that this 5000 km diameter body may have Mare areas like 
Earth's Moon and a few large bright rings which may be ice or near 
specular reflection from smooth surface features (37). Pioneer 10 
is moving out of the solar system, but in a remarkable feat of space- 
craft navigation, Pioneer II has now been targeted to fly by Saturn 
in 1979. So precisely can the trajectory be controlled that scientists 
are discussing whether maximum data would be obtained by a pass 
outside the rings, through the rings, or between the rings and the 
parent body. : 
Exploration of Venus 
  
Mariner 10 was launched on November 3, 1973, and encountered the 
planet Venus on February 5, 1974. The spacecraft carried two 
identical vidicon cameras with eight interchangeable filters (38). 
Each camera had dual focal lengths: 1500 mm narrow angle and 62 mm 
wide angle. The vidicon format was 9.6 x 12.5 mm with 700 scan lines 
and 832 samples per line, and eight bit grey level encoding. As the 
spacecraft passed Venus at a minimum altitude of 5300 km, about 7800 
pictures were taken, primarily in the ultraviolet band in the hope of 
penetrating the dense atmosphere. Resolution varied from 130 km to 
20 m. The pictures show enormous meteorological patterns. 
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