Greemhouse on Venus

Greenhouse on Venus

The surface temperatures on Venus, as deduced from radio astronomy and confirmed by direct spacecraft measurements, are around 480 C or 900 F, hotter than the hottest household oven.The corresponding surface pressure is 90 atmospheres, 90 times the pressure we feel from the Earth’s atmosphere, the equivalent of the weight of water 1 kilometer below the surface of the oceans. To survive for long on Venus, a space vehicle would have to be refrigerated as well as built like a deep submersible.

Something like a dozen space vehicles from the Soviet Union and United States have entered the dense Venus atmosphere, and penetrated the clouds; a few of them have actually survived for an hour or so on the surface (Pioneer Venus was a successful US mission inn1978-79, combining an orbiter and four atmospheric entry probes, two of which briefly survived the inclemencies of the Venus surface. 

A little greenhouse is a good thing. Image: Mosaic Moving © Elena

There are many unexpected developments in mustering spacecraft to explore the planets. This is one of them: Among the instruments aboard one of the Pioneer Venus entry probes was a net flux radiometer, designed to measure simultaneously the amount of infrared energy flowing upwards and downwards at each position in the Venus atmospheres. The instrument required a sturdy window that was also transparent to infrared radiation. A 13,5-karat diamond was imported and milled into the desired window. However, the contractor was required to pay a $12,000 import duty. Eventually, the U.S. Customs service decided that after the diamond was launched to Venus it was unavailable for trade on Earth and refunded the money to the manufacturer.

The global temperature on the Earth would be below the freezing point of water if not for the greenhouse effect. It keeps the ocean liquid and the life possible. A little greenhouse is a good thing. Like Venus, the Earth also has about 90 atmospheres of carbon dioxide; but it resides in the crust as limestone and other carbonates, not in the atmosphere.

If the Earth were moved only a little closer to the Sun, the temperature would increase slightly. This world drive some of the CO2 out of the surface rocks, generating a stronger greenhouse effect, which would in turn incrementally heat the surface further. A hotter surface would vaporize still more carbonates into CO2, and there would be the possibility of a runaway greenhouse effect to very high temperatures. This is just what we think happened in the early history of Venus, because of Venus’ proximity to the Sun. The surface environment of Venus is a warning: something disastrous can happen to a planet rather like our own.