An investigation of the absorption spectra of water and ice, with reference to the spectra of the major planets

Abstract

The spectra of the light of the sun reflected from the major planets—Jupiter, Saturn, Uranus and Neptune—were photographed by Slipher in 1909. These spectra showed a general similarity in that there were a number of absorption bands superimposed on the ordinary solar spectrum. The intensity and width of these absorptions varied from planet to planet, increasing in general from Jupiter to Neptune in the order quoted. Of the chemical identity of the bands little is known. Some—C and F, fig. 4, for example—can be attributed to absorption by atomic hydrogen in the atmospheres of the planets; others might be due to water-vapour, though other water-vapour bands do not appear. The outstanding unidentified bands which are common to the spectra of the four planets are (see fig. 4, Plate 10):— ( a ) At λ = 5430 Å.—A rather weak band in the spectra of Jupiter and Saturn, but very strong in those of Uranus and Neptune. ( b ) At λ = 6190 Å.—This is the mid-point of a conspicuous and dense band appearing in the spectra of all the four planets, broadening from a width of some 50 Å in that of Jupiter to some 200 Å in that of Neptune. Although quite strong in the spectrum of Jupiter, it showed no tendency to become resolved in the high dispersion plates taken of the spectrum of this planet. ( c ) A strong double band at λ = 7200 to 7260 Å recorded in the spectra of Saturn and Jupiter, and probably just as strong in those of Uranus and Neptune, but not recorded because of the insensitiveness of the plates in this region.