At a wavelength of 1.58 microns, we sense sunlight reflected from cloud particles with virtually no absorption by Jupiter's gases. Thus, the variations from one region to the next indicate changes of the reflectivity (albedo) of cloud particles. The Great Red Spot, toward the lower right, reflects sunlight in much the same way as the surrounding clouds and does not appear very distinct from them.
At a wavelength of 3.8 microns, we sense two sources of radiation. One is sunlight reflected from cloud particles in Jupiter's upper troposphere which has not been extinguished by weak methane (CH4) gas absorption. The Great Red Spot is seen as a high cloud on the right, just below the center; the brightest reflection - and probably the highest cloud particles in this region - are detected in discrete plumes just north of the equator, close to the latitude in which the Galileo Probe will enter on December 7. The other source of radiation comes from emission by H3+ from an airglow which covers the planet and is most pronounced at the edge of the disk (the limb) and from auroral emission near the poles. This image has captured some auroral H3+ emission near the north pole.
At a wavelength of 2.3 microns, we sense sunlight reflected from cloud and haze particles higher up - in Jupiter's lower stratosphere - which have not been extinguished by gaseous methane (CH4) and molecular hydrogen (H2) absorption. Here the Great Red Spot is a prominent feature of high-altitude particles, and - although faint - it is followed by an oscillating stream of particles to the east (left) in its downwind wake. The most prominent features are the particulate caps covering the poles. From mid-latitudes toward the south pole, the moderate reflecting particulates are mostly remnants of particles remaining from impacts of Comet Shoemaker-Levy 9 fragments near 45 deg.S lat., now distributed rather uniformly over longitudes and migrating far to the south and somewhat north of the impact latitude.
At a wavelength of 4.85 microns, we are sensing heat from Jupiter, denoted by the false red shading. The darkest regions correspond to emission from temperatures near 185 Kelvins (-190 deg. F) and the warmest regions to temperatures near 255 Kelvins (-64 deg. F), indicating emission from 1 - 5 bars of atmospheric pressure in Jupiter. The brightest spots are discrete regions which are locally clear of obscuring clouds, known as ``hot spots''; they are one of the special targets planned for the atmospheric investigations by the Galileo Orbiter instrument teams. Note that there is a relatively bright (clear) but broken band to the north of the Great Red Spot. There are also bright rings around several of the visibly white oval features south of the Great Red Spot.
This image is available in gif format via anonymous ftp to lono.jpl.nasa.gov (22.214.171.124) in pub/irtf as galley95jul26.gif. It is catalogued as JPL color negative P-46230 BC.
Webmaster's Note: As of 2/5/96, anonymous FTP to lono.jpl.nasa.gov was not available. This FTP site may or may not exist now.