Molecular Monday: Venus’s Sulfuric Acid

Welcome to the first official installment of Molecular Mondays, a new series here on Planet Pailly where we take a closer look at the atoms and molecules that make up our universe. Today, we’ll be talking about sulfuric acid, specifically the sulfuric acid that is so disturbingly prevalent in Venus’s upper atmosphere.

Mr04 Melting Spaceship

How to Make Sulfuric Acid

The first step is for sulfur dioxide to pick up an extra oxygen atom, creating sulfur trioxide. Sulfur trioxide then reacts with water, yielding sulfuric acid.

SO2 + O -> SO3

SO3 + H20 -> H2SO4

On Earth, we make sulfuric acid in factories, and it has many scientific and industrial uses. But on Venus, this is happening not in tanks or vats but in the open air, far above the planet’s surface.

Venus’s Sulfur Cycle

Sulfur containing chemicals like sulfur dioxide rise through the air on Venus, possibly originating from Venus’s many volcanoes. These chemicals get zapped by ultraviolet radiation from the Sun, causing sulfur and oxygen atoms to separate and recombine. One possible recombination is sulfur trioxide, which then reacts with traces of water vapor hanging around in Venus’s atmosphere.

Sulfuric acid then condenses into clouds. Sooner or later, the clouds condense further, producing rain: the most horrible rain you could possibly imagine. Fortunately, this sulfuric acid rain never reaches the planet’s surface (not that it matters much because if you’re on the surface of Venus, you’re already dead).

Thermal Dissociation of Sulfuric Acid

Because Venus’s surface temperature approaches 900 degrees Fahrenheit, the sulfuric acid rain begins to evaporate. In fact, the temperature is so high that sulfuric acid molecules break apart in a process called thermal dissociation.

What we’re left with are water vapor and sulfur containing chemicals like sulfur dioxide. The water and sulfur compounds start rising through the atmosphere, and the process begins again, repeating over and over, ensuring that Venus’s atmosphere maintains high levels of corrosive acid… forever.

It’s almost like Venus is being deliberately evil.

Mr04 Evil Venus


Sulfuric Acid from Essential Chemistry Industry Online.

Aerosols and Clouds on Earth and Venus from the University of Colorado, Boulder.

Photolysis of Sulphuric Acid as the Source of Sulphur Oxides in the Mesosphere of Venus from Nature Geoscience.

The Sulfur Cycle on Venus: New Insights from Venus Express from the 2009 Lunar and Planetary Science Conference.

Recommended Reading

Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet by David Grinspoon.

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