They will learn how Venus permanently lost an amount of water equivalent to the amount of water on Earth.

But at some point everything changed and a disaster occurred. There, with dense clouds of carbon dioxide blanketing the atmosphere, the most powerful and brutal greenhouse effect the solar system has ever known occurred, causing surface temperatures to rise to more than 400 degrees today. In the process, all the water evaporated, and most of it went into space. What little remains of Venus is dissolved in its dense atmosphere and continues to “escape” into space. Despite this, this ancient evaporation process cannot explain why Venus is as dry as we see it today, and how it can continue to lose water today.

Now a team of planetary geologists from the University of Colorado Boulder has found a mechanism that could explain this mystery. The results of their research have just been published in the journal Nature, and they fill a large gap in what scientists call the “history of water on Venus.”

Using computer simulations, the team found that hydrogen atoms in the planet’s atmosphere are being “ejected” into space through a process known as “dissociative recombination”, causing Venus to lose about twice as much water each day than previously thought. If the same process is at work in other solar systems, these results could help explain what is happening to water on a large number of planets in the galaxy.

“Water,” explains Erin Kangi from the Laboratory of Atmospheric and Space Physics (LASP) at the University of Colorado and co-author of the study, “is really important for life. “We need to understand the conditions that support liquid water in the Universe, and which may also be responsible for the very dry state of Venus today.”

One hundred thousand times less water

And Venus, the researcher adds, is completely dry. If we took all the water on Earth and spread it across Venus, we would end up with a global layer of liquid about 3 km deep. But if we did the same with the water left by Venus, which is “trapped” in the air, we would get a layer of only 3 cm, which is barely enough to wet our toes.

“Venus has 100,000 times less water than Earth,” said Michael Chaffin, also of LASP and lead co-author of the study, “even though it is essentially the same size and mass.”

Using their computer models, the researchers studied Venus as if it were a giant chemistry laboratory, focusing on the various reactions occurring in the planet’s turbulent atmosphere. Thus, the team discovered that the culprit of the “leak” could be a certain molecule called HCO+ (an ion formed by a hydrogen atom, one carbon atom and another oxygen atom), present in the upper atmosphere of Venus. ‘water on the planet.

For Kanga, this discovery represents an important clue to why Venus, which in the past was certainly identical to Earth, can become the hell it is today. According to the researcher. “We’re trying to figure out what chain of small changes happened on each planet (Earth and Venus) to bring them to these very different states.”

Guilty Molecule

In their paper, Chaffin and Kangi explain that in the upper atmospheres of planets, water mixes with carbon dioxide to form HCO+. In fact, in previous studies, researchers had already reported that this same molecule could also be responsible for Mars losing most of its water.

On Venus, the mechanism works like this: HCO+ is constantly formed in the atmosphere, but individual ions do not live long. Free electrons from the atmosphere essentially find these ions and recombine with them, splitting them in two. During this process, hydrogen atoms are removed and may even escape completely into space, thus depriving Venus of one of its two components of water.

Chaffin and Kangi calculated that the only way to explain Venus’s current dry state is to assume that the planet contains much larger amounts of HCO+ in its atmosphere than expected. But there’s a problem: HCO+ has never been observed around Venus until now. The researchers say they never had the right tools to test it.

In fact, while dozens of missions have visited Mars in recent decades, the number of spacecraft sent to Venus has been much smaller. Moreover, none of them were equipped with instruments capable of detecting the HCO+ that controls the “escape route” the team recently discovered. In fact, according to Chaffin, “one of the most surprising findings of this work is precisely that HCO+ should be one of the most abundant ions in the atmosphere of Venus.”

Until now, Kangi concludes, “there haven’t been many missions to Venus. But newly planned missions will leverage decades of experience and growing interest in Venus to study the extremes of planetary atmospheres, evolution and habitability.”