Encyclopedia of the Solar System 2nd ed

702 Encyclopedia of the Solar System

(a) (b)

FIGURE 7 (a) A radio photo of Jupiter at a wavelength of 2 cm, integrated over 6–7 hours, so any longitudinal structure is smeared out.
The data were obtained with the VLA on 25 January 1996. The angular resolution is 1.4,” which was 0.044 Jupiter radii at the time of the
observations. (I. de Pater et al., 2001, Comparison of Galileo probe data with ground-based radio measurements,Icarus 149 , 66–78.) (b)
A comparison of the North Equatorial Belt of Jupiter at an infrared wavelength of 5μm (IRTF, NASA’s Infrared Telescope Facility) and
radio wavelength of 2 cm (VLA). The latter image is constructed from the same data as displayed in Fig. 7a, but using novel new data
reduction techniques. (R. J. Sault et al., 2004, Longitude-resolved imaging of Jupiter atλ=2 cm,Icarus 168 , 336–343.)

In recent years, an algorithm has been developed to con-
struct longitude-resolved images of Jupiter, and these maps
reveal, for the first time, hot spots at radio wavelengths that
are strikingly similar to those seen in the infrared. An exam-
ple of Jupiter’s North Equatorial Belt is shown in Fig. 7b. At
radio wavelengths, the hot spots indicate a relative absence
of NH 3 gas, whereas they suggest a lack of cloud particles
in the infrared. Models show that ammonia must be de-

pleted down to pressure levels of∼5 bar in the hot spots,

the approximate altitude of the water cloud.

2.5.3 SATURN

Images of Saturn’s microwave emission at different viewing

geometries are shown in Fig. 8. The planet itself is visi-

ble through its thermal emission. The emission from the

FIGURE 8 Radio photographs of

Saturn at 2 and 3.6 cm, at different

viewing aspects of the planet.

(a) 3.6 cm, 1990; (b) 2 cm, 1994;

(c) 2 cm, 1998; (d) 3.6 cm, 2002.

(Dunn, D.E., I. de Pater, and L.A.

Molnar, 2006. Examining the wake

structure in Saturn’s rings from

microwave observations over

varying ring opening angles and

wave lengths. (Icarus, in press.)