Life in the Clouds of Venus?

Abstract

WHILE the surface conditions of Venus make the hypothesis of life there implausible, the clouds of Venus are a different story altogether. As was pointed out some years ago¹, water, carbon dioxide and sunlight—the prerequisites for photosynthesis—are plentiful in the vicinity of the clouds. Since then, good additional evidence has been provided that the clouds are composed of ice crystals at their tops^2,3, and it seems likely that there are water droplets toward their bottoms⁴. Independent evidence for water vapour also exists⁵. The temperature at the cloud tops is about 210° K, and at the cloud bottoms is probably at least 260–280° K (refs. 4 and 6). Atmospheric pressure at this temperature level is about 1 atm.⁷. The observed planetary albedo falls steeply in the violet and ultra-violet⁸, which accounts for the pale lemon yellow colour of Venus. The albedo decline would not be expected for pure ice particles, and must therefore be caused by some contaminant. Dust, ozone, C₃O₂ and other gases may possibly explain these data but, whatever the explanation, the ultra-violet flux below the clouds is likely to be low. If small amounts of minerals are stirred up to the clouds from the surface, it is by no means difficult to imagine an indigenous biology in the clouds of Venus. What follows is one such speculation.