By Jonny Lupsha, Wondrium Staff Writer
Venus’s surface is covered by toxic acid rain clouds, making it hard to study. Additionally, its surface temperature is more than 860 degrees Fahrenheit, making landing spacecraft an impossibility. A low-frequency radio signal may offer clues.
Theoretically, Venus shouldn’t be too dissimilar to Earth. Its diameter and its average planet density are 95% as much as Earth’s and some scientists have referred to Venus as “Earth’s twin.” However, planetwide acid rain clouds and an atmospheric pressure over 90 times that of Earth’s (at sea level) help make it an inhospitable wasteland—and one that’s hard to study.
However, a recent flyby of NASA’s Parker Solar Probe captured the first low-frequency radio signal in Venus’s ionosphere in 30 years, as it traveled through the layer of Venus’s upper atmosphere. Compared to previous data, Venus’s ionosphere is now thinner, possibly due to solar cycles.
In her video series A Field Guide to the Planets, Dr. Sabine Stanley, a Bloomberg Distinguished Professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins University, outlined some of the differences between the “twin” planets.
Atmospheric Conditions
From the ground up, how do Earth and Venus compare?
“On Earth, the bottom layer of the atmosphere, called the troposphere, extends from the surface up to an average of about 10 kilometers,” Dr. Stanley said. “This is the layer of the atmosphere where most of the weather happens—three-quarters or more of all atmospheric mass is here. Venus has a troposphere, but it extends from the surface up to about 65 kilometers, so it’s, on average, 6-1/2 times taller.”
However, according to Dr. Stanley, despite the incredible height of Venus’s troposphere, the other layers of its atmosphere are so much thinner than those on Earth that they cancel out the troposphere’s extra height and the whole atmosphere is actually only half as high as Earth’s.
“What’s in the air is also very different,” she said. “Venus’s atmosphere is overwhelmingly carbon dioxide; Earth’s atmosphere is 3/4 nitrogen. It turns out that Earth, as a planet, still has about the same amount of carbon dioxide as Venus; it’s just that Earth removes it from the atmosphere.”
Earth, she said, buries its carbon dioxide in carbonate rocks, which mostly happens in the oceans due to plate tectonics; while our plants convert land-based carbon dioxide to air. Venus has neither oceans, nor plate tectonics, nor plants.
If You Can’t Stand the Heat…
“In addition to fiery temperatures, the hellish atmosphere of Venus even offers brimstone—that’s an old word for sulfur,” Dr. Stanley said. “The oxygen hanging around in the atmosphere pairs up with sulfur erupted by volcanoes to form clouds made of sulfuric acid, also known as vitriol. That’s a highly corrosive acid that easily causes severe burns in contact with skin and can even dissolve metals and stone.”
Dr. Stanley said the acid clouds form because of an atmospheric interaction between carbon dioxide, ultraviolet light, and sulfur dioxide that was emitted from volcanoes long ago. The carbon dioxide is broken up into atomic oxygen and carbon monoxide by the ultraviolet light; then the atomic oxygen reacts with sulfur dioxide to create sulfur trioxide. Finally, the sulfur trioxide combines with traces of water vapor in Venus’s atmosphere to form sulfuric acid.
“You might think things get better below the cloud level on Venus, but it turns out that, like on Earth, clouds can lead to rain, and the sulfuric acid clouds on Venus lead to sulfuric acid rain down to about 20-30 kilometers altitude,” she said.
“Down at those altitudes, it’s already so hot that the sulfuric acid evaporates and so [it] doesn’t actually hit the surface.”
Of course, since that acid and the temperatures of Venus can melt lead, flyby recordings of radio signals may be our best chance at observing the “veiled greenhouse” planet for now.