Wednesday, October 28, 2020

This post was originally published on Science News

Home Science Hope for life on Venus survives for centuries against all odds

Hope for life on Venus survives for centuries against all odds

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This post was originally published on Science News

If you’re looking for an exemplar of mastering multiple identities, find a telescope and point it at Venus.

In both astronomy and popular culture, Venus has always assumed a diversity of guises. Morning star, evening star. Goddess. Planet. Frankie Avalon song. A plant that eats flies. And the realm ruled by women in the unforgettable film Queen of Outer Space (starring Zsa Zsa Gabor as the nemesis of the evil queen).

So it’s not surprising that Venus enjoys sufficient celebrity status to warrant big-type headlines when it makes news, or at least a lot of social media hype. In the latest such instance, all it took was a whiff of a noxious gaseous chemical in the planet’s clouds, hinting that Venus might harbor life, to stop the presses and start the tweetstorms. After all, life on Venus would be a big surprise. Scientists have long considered it the hell of the solar system, hotter than molten lead and with an unbreathable atmosphere.

Yet, as it was so ably reported by Lisa Grossman for Science News, the chemical in question, phosphine, is no guarantee of life on Venus. It’s just that the known nonbiologic ways to make phosphine do not seem plausible in the Venusian environment. Phosphine’s persistence in the clouds shrouding Venus suggests something must be currently producing it — otherwise the sulfuric acid in the planet’s upper atmosphere would have destroyed any signs of the gas by now. So phosphine might be a signal of life — perhaps some form of anaerobic bacteria (which do not require oxygen), as phosphine would be deadly to life that relied on oxygen.

On the other hand, maybe there’s just a gap in Earthling chemistry textbooks, and some weird geochemical reactions produce Venusian phosphine. That’s probably a better bet than airborne anaerobic alien organisms. Phosphine as evidence of life on Venus may turn out to be as reliable as the famous “canals” once regarded as evidence for life on Mars.

Still, hope for life on Venus never dies. In centuries past, in fact, many scientists simply assumed that Venus possessed life. In the late 17th century, Bernard le Bovier de Fontenelle, a French popularizer of science, surmised Venus to be inhabited by a gallant race of lovers. “The climate is most favorable for love matches,” he wrote. About the same time, the Dutch physicist and astronomer Christiaan Huygens contemplated life on Venus. Venusians would receive twice the light and heat from the sun as Earthlings do, he knew, but noted that Earth’s tropics, though much hotter than northern lands, are successfully occupied by people. For that matter, Huygens believed much hotter Mercury to be populated as well, and that the Mercurians would no doubt consider Earth much too cold and dark to support life.

In the 19th century, spectroscopic examination of Venus suggested that its atmosphere was similar to Earth’s, containing water vapor and oxygen. Since Earth’s atmospheric composition owed so much to life, it seemed obvious that life — at least plants— must exist on Venus as well. “If there be oxygen in the atmosphere of Venus, then it would seem possible that there might be life on that globe not essentially different in character from some forms of life on the earth,” astronomer Robert S. Ball wrote in his widely read late 19th century book The Story of the Heavens. “If water be present on the surface of Venus and if oxygen be a constituent of its atmosphere, we might expect to find in that planet a luxuriant tropical life.”

As late as 1918, Svante Arrhenius, a Nobel chemistry laureate, estimated that water was especially abundant on Venus, with humidity six times the average on Earth. “We must therefore conclude that everything on Venus is dripping wet” — thereby accelerating the growth of vegetation, Arrhenius wrote.

But the early observations of Venus’ atmosphere were crude. About a century ago, refined techniques at the Mount Wilson Observatory in California contradicted the previous findings; oxygen and water vapor actually seemed scarce in the Venusian clouds. (In fact, as spacecraft visiting Venus in recent decades have shown, the air there is nearly all carbon dioxide with a little bit of nitrogen, plus only slight traces of water.) “It may be that the exacting conditions for the origin of life have not been satisfied” on Venus, Charles E. St. John and Seth B. Nicholson wrote in 1922 in the Astrophysical Journal.

Of course, it was possible that conditions on the surface, hidden by the thick clouds, might still allow life to find a way. 

“There is a possibility that the atmosphere of Venus is permeated with a finely divided dust, a possible product of intense volcanic activity, which would act as an excellent reflector of the sun’s rays and would at the same time effectually conceal the surface,” Isabel Lewis of the U.S. Naval Observatory wrote in Science News-Letter, the predecessor of Science News, in 1922. In 1926, the prominent astronomer Harlow Shapley maintained that in the solar system, Venus “more nearly fulfills the conditions [for life] than any planet other than the Earth…. But we cannot penetrate the dense covering of clouds and seek out the secrets of its surface.”

In 1927, Science News-Letter writer Frank Thone surveyed the prospects for life on other planets and declared Venus “the darling of the solar system” (excepting Earth, of course). While Mars seemed “wry and withered,” he wrote, “our sister Venus seems to have the vigor and sap of life in her.”

Yet as Thone acknowledged, the thick atmosphere guarding Venus’ surface from view made the question of life there unanswerable — probably, Thone guessed, for many generations.

And so today, the mystery remains unsolved. Phosphine sightings leave the question of whether Venus hosts life in a situation similar to that of Mars, long ago, when the newspaper publisher William Randolph Hearst (legend has it) cabled an astronomer asking for an article on the topic. “Is there life on Mars? Please cable one thousand words,” Hearst wrote. To which the astronomer cabled back: “Nobody knows. Repeat 500 times.”

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