Venus: Our toxic twin

Venus: Our toxic twin


Last month we looked at the genesis of the Earth, and the UN’s Global assessment Report that human society is in jeopardy from the accelerating decline of the Earth’s natural life support systems.

This month I think we should look at what was once upon a time considered to be our twin sister, Venus, on the inner edge of what astronomers call the habitable zone; a place where life could have started, and with Mars on the outer edge of that zone.

Early observations showed it was a similar age and size to the Earth, with a substantial atmosphere. Its impenetrable cloud cover gave science fiction writers free reign to speculate on conditions at its surface. Being closer to the Sun it was thought to have oceans, swamps and deserts.

Nobel Prize winner Svante Arrhenius, deciding that Venus’s cloud cover was necessarily water, decreed in the Destinies of the Stars, that “A very great part of Venus is no doubt covered with prehistoric swamps” and compared Venus’ humidity to the tropical forests of the Congo.

Even Zsa Zsa Gabor managed to live there in Queen of Outer Space and after a bit of bother…… the Venusians are free once again to enjoy the love of men?  Sadly, for men on Earth, I can assure you there are no women on Venus, and the name is a bit misleading.

As long as no-one could peer behind its all concealing cloud cover everything and anything was possible.

Not until the advent of space probes was the true nature of Venus revealed; a world just a bit too close to the Sun, receiving twice as much solar energy as Earth does. A dim world of intense heat and volcanic activity. Similar in size to Earth, Venus’ thick toxic atmosphere traps heat in a “runaway greenhouse” effect. The scorched world has temperatures hot enough to melt lead at the surface. Today, Venus’ atmosphere contains only 0.002% water, which is a million times less than that present in the Earth’s atmosphere.

Venus’ atmosphere is 96% carbon dioxide. On Earth the carbon cycle starts when carbon dioxide is belched out by volcanoes, or exhaled by life, and finds itself in the atmosphere where it dissolves and rains out. At the surface it becomes locked up in carbonate rocks, or descends back into the Earth’s mantle via subduction caused by plate tectonics. In fact, there is as much carbon dioxide in Earth’s carbonate rocks as there is in Venus’ atmosphere.

Earth and Venus were born 4.6 billion years ago from the same inter stellar dust cloud and in a similar location, and some planetary scientists believe that in their early history the young Earth and the young Venus probably were similar, with similar amounts of water.

So could Venus have once been a Blue planet! Climate modelling software suggests it could, with a temperate climate protected by a shield of thick clouds that reflected much of the Sun’s heat and light back into space. It suggested there could have been shallow oceans covering two thirds of the surface. Indeed, with Venus’s glacial rotation (243 days), the slowest in the solar system, and retrograde spin axis (not understood), then the climate could have remained habitable until about 700 million years ago. Both Earth and Venus could have harboured life at the same time.

So, what happened? Well the entire surface seems to be only 700 million years old and the only thing that could be responsible is massive volcanism. There are more than 10,000 volcanoes counted so far on Venus. Massive amounts of carbon dioxide would have belched out. Temperatures would rise rapidly; the oceans would evaporate until the skies filled with water vapour. With so much carbon dioxide in the air and nothing to remove it, the planets paradise is doomed and only hell awaits. It’s a runaway greenhouse effect and nothing could stop it.

Today the temperature at the surface is a sweltering 470 degrees Celsius, the atmosphere is a crushing 90 times that of the Earths’ and it rains sulphuric acid. It’s a sobering thought that we have as much carbon dioxide locked away safely on Earth as in Venus’ atmosphere, but our atmosphere contained only 250ppm pre-industrial revolution. It’s already risen to 380ppm since then and rising. The warning signs are there, we ignore them at our peril. Earth is lucky it was born in the middle of the Goldilocks Zone, one planet too hot (Venus), one planet too cold (Mars).

Venus is what we might get if we don’t start treating our planet with the respect it deserves.

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