On the composition of the Venus clouds

Abstract

Recently, using near‐infrared spectra of Venus obtained from a high‐altitude balloon, Bottema, Plummer, Strong, and Zander have concluded that the Venus clouds are composed of H2O ice. This conclusion was supported by Sagan and Pollack, who, moreover, bracketed the particle radii between 7.5 and 10 μ. Because it contradicts previous statements by Kuiper and Moroz that H2O ice is not present, we decided to re‐examine the relevant spectroscopic data and their interpretations. To assist us, Miller and Boese recorded long path absorption spectra of pure CO2 gas. Two salient features emerge from our study: the absence of any absorption other than CO2 both at 1.5 μ and at 2.0 μ. Since cirrus and laboratory ice clouds both exhibit strong absorptions centered at these wavelengths, it is clear that the Venus clouds cannot be similar to these. There remains a possibility that the major scatterers could be H2O ice—if the particle sizes are submicron, the absorption bands would diminish in intensity. It is argued, however, that the existence of the required abundance of such particles on a planet‐wide basis is improbable. Accordingly the major scatterers of radiation are almost certainly not composed of H2O ice. Various candidates for the particles are mentioned, but no positive spectroscopic evidence to support a particular one is advanced.

Comments on the paper by D. G. Rea and B. T. O'Leary, ‘On the composition of the Venus clouds’

“…In a recent paper Rea and O'Leary (1968) examined the cases for and against ice clouds on Venus and concluded ". .…”

Ephemeral Ice Clouds in the Upper Mesosphere of Venus

“…Through differing analyses of infrared absorption seen at 3 μm from high altitude balloon measurements in the 1960s, both Bottema et al. (1965) and Pollack and Sagan (1968) suggested water ice clouds could explain the observed absorbances, although a rebuttal by Rea and O'Leary (1968) suggested this was possible only if the ice particles were submicron in size. Turco et al.…”

The Atmospheres of Mars and Venus

“…Figure 5 shows low-resolution spectra of Venus at wavelengths 0.2-4.0 /z (Moroz 1965, Bottema et al 1965, Irvine 1968, Kuiper 1969b). Absorptions at 1.5, 2.0, and beyond 3.0 # are characteristic of ice (Bottema et al 1965, Pollack & Sagan 1968, Plummet 1970, but COg aseous absorptions may account for the features observed in the Venus spectrum at 1.5 and 2.0 # (Rea & O'Leary 1968, Hansen & Cheyney 1968. On the other hand, ice is not a strong absorber below 0.4 ~, although many other solids are.…”