Life on Venus may never have been possible

After all, Venus may not be such a tempting target for alien hunters.

In recent years, researchers have increasingly come to regard Venus, the second rock from the sun, as a possible abode for life. For example, modeling studies have suggested that ancient Venus had large oceans and a pleasant climate that could have persisted for several billion years.

Venus is famous today, of course; its surface is completely dry and hot enough to melt lead. But some scientists have argued that life on Venus, if it ever existed, could persist there still, floating in clouds some 30 miles (50 kilometers) up, where temperatures and pressures are similar to what we enjoy at the level of the Earth. sea ​​here on Earth.

However, a new study sheds some cold water on those hopes.

Related: Photos of Venus, the Mysterious Planet Next Door

Dueling models of ancient Venus

Like all newborn planets, young Venus was extremely hot, too warm for oceans of liquid water. The available water was practically vaporized, creating sauna conditions on a planetary scale.

Earlier life-friendly modeling work determined that the planet cooled enough to host liquid surface water thanks in large part to clouds, which returned a large amount of solar radiation back into space. The “dim young sun” was a contributing factor as well; In the early days of the solar system, our star was only 70% brighter than it is now.

In the new study, which was published online today (October 13) in the journal Nature, scientists led by Martin Turbet, a postdoctoral researcher at the Geneva Astronomical Observatory in Switzerland, simulated the weather of ancient Venus using a new model. . And they got very different results.

Turbet and his team found that conditions on young Venus likely limited the clouds to the night side of the planet, where they were worse than useless when it came to establishing life. (Venus is not tidal locked to the sun, so it does not have a permanent nightside – the term here refers to any hemisphere that is facing away from the sun at the time.)

Not only did these clouds not bounce back sunlight, they actually warmed Venus through a greenhouse effect, trapping a lot of heat. So Venus never got cold enough for rain to fall and for rivers, lakes and oceans to form.

“If the authors are correct, Venus was always hell,” wrote astronomers James Kasting and Chester Harman of Penn State University and NASA’s Ames Research Center, respectively, in an accompanying article. “News & Views “in the same issue of Nature. (Kasting and Harman are not members of the study team.)

A more in-depth study of the surface of Venus could provide some clarity on the planet’s ancient climate. For example, Kasting and Harman point to “highly deformed regions” of the planet known as tesserae, which are believed to be similar in composition to continental rocks on Earth.

“On our planet, such rocks are formed by metamorphic processes (in which minerals change shape without melting) that occur in the presence of liquid water,” Kasting and Harman wrote. “If the tiles turned out to be basaltic, like normal seafloor on Earth, liquid water would not have been needed to generate them, further supporting the hypothesis of Turbet and his colleagues.”

NASA’s newly selected VERITAS mission (short for “Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy”), scheduled to launch in 2028, will study the tiles from orbit, if all goes according to plan. But it may take a Venus lander to gain a firm understanding of these intriguing features, Kasting and Harman wrote.

Implications for Earth and beyond

The new study also found that Earth would likely have gone the Venusian route if the sun had been a little brighter a long time ago – a young sun with 92% current brightness instead of 70% would likely have relegated our planet to the state. greenhouse, according to the model developed by Turbet and his team.

The results also have implications for worlds orbiting other suns and for researchers seeking to understand them, as Kasting and Harman noted.

“Exoplanets that orbit near the inner edge of the conventional habitable zone, where liquid water may exist on a planet’s surface, might not be truly habitable,” the duo wrote.

Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for extraterrestrial life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.

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