Word: infra
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Target for the night was Mars, riding ever higher in the sky as the night advanced. After a little guidance trouble, the soaring scope found the planet and focused its concentrated reddish light into a spectrometer that measured infra-red rays, recorded the readings on magnetic tape and transmitted them simultaneously to the ground. After a 12-hr., 700-mile flight, the balloon and telescope landed gently in Tennessee...
...Infra-red readings also showed the temperature on top of the cloud deck to be about -30° F. It varied little over the planet except in one spot at the southern end of the boundary between light and dark, where it fell to about -50° F. No one is sure what this means. Perhaps the clouds are higher or more opaque at this point. Perhaps a surface feature, such as a high mountain, forces them upward...
...instruments made another important observation: the limb (edge) of the Venusian disk appears darker than the center. This "limb darkening" means that microwaves and infra-red radiation really originate at the surface or at some level below the top of the atmosphere. Rays coming from the limb must pass slantwise through a greater thickness of atmosphere, and so appear weaker. This rules out one of the leading theories about the Venusian atmosphere: that it is highly ionized on top and therefore glows, making the planet appear hotter than it really is. Such an atmosphere would be brighter at the edges...
Physicist Louis D. Kaplan of the University of Nevada and JPL, who helped design Mariner II's infra-red experiment, thinks that at ground level, Venus' atmospheric pressure may be 10 to 20 times that of Earth. Its dry, unbreathable air contains perhaps 10% carbon dioxide (v. .03% for Earth) and probably a little nitrogen. The clouds are so dense that the surface is probably dark. Radar waves bounced off Venus indicate rather uncertainly that there may be both mountains and smooth places, as on the earth...
...they are hydrocarbon droplets similar to the water droplets in earthly clouds. The droplets condense in the cool top of the atmosphere, but stay in vapor form in the lower parts, where the temperature rises above 200° F. So the dark Venusian surface has clear, compressed, oily air. Infra-red rays from the sun penetrate both clouds and atmosphere, but are hindered by the CO2 when they try to escape. This trapped energy keeps the surface so hot that no life known on Earth could possibly survive there...