Scientists may have identified a molecule that played a key role in robbing Venus of its water and turning this planet into the barren, hellish world we see today.
Venus is often called “Earth’s twin” because both planets are approximately the same size and density; they are also both rocky planets in the inner solar system. Yet Venus could not be less like Earth in many crucial respects.
While our planet is teeming with life, Venus, the second planet from the sun, is a virtual hell. It is the hottest planet in the solar system (even hotter than Mercury, which is closest to the Sun), and has temperatures of about 880 degrees Fahrenheit (471 degrees Celsius). That’s hot enough to melt lead. Plus, Venus has some pretty scary surface pressure.
Importantly, Venus also lacks a key element for life that is abundant here on Earth: water. This is despite the fact that the planet is within the sun’s so-called ‘Goldilocks Zone’, referring to the area around our star that is neither too hot nor too cold for liquid water to exist – and it’s also despite the fact that scientists know Venus probably used to have water.
Related: Zoozve – the strange ‘moon’ of Venus that got its name by accident
It is believed that Venus had as much water as Earth billions of years ago, but at some point in its evolution, clouds of carbon dioxide in the planet’s atmosphere caused the solar system’s most intense greenhouse effect. This caused temperatures to rise to the point we see today. That caused the planet’s water to evaporate and be lost to space.
However, even considering this process, scientists don’t know how Venus became so desert-like or how it continues to lose what little water it has left to space. Now a team of scientists from the University of Colorado Boulder may have discovered the secrets of this process by telling what they call “the water story on Venus.”
“Water is really important for life,” said Eryn Cangi, co-team leader and scientist at the Laboratory for Atmospheric and Space Physics (LASP, in a statement). “We need to understand the conditions that support liquid water in the universe and that may have caused the very dry state of Venus today.
“We’re trying to figure out what small changes have happened on each planet to drive them into these vastly different states.”
Hey, neighbor! Have a cup of water left over?
To put the difference in water content of neighboring planets Earth and Venus into context, Cangi explained that if all the water on our planet were evenly distributed over its surface, it would create a global layer almost 2 miles (3.2 kilometers) deep. If you did the same for Venus, removing the remaining water from the atmosphere would create a global layer only 3 centimeters deep.
“Venus has 100,000 times less water than Earth, even though it is basically the same size and mass,” Michael Chaffin, co-team leader and fellow LASP scientist, explained in the statement.
To determine how it reached its current state, Cangi, Chaffin and colleagues used computer models of the planet, treating it almost like a giant chemistry laboratory. This allowed them to look more closely at the various reactions taking place in Venus’ swirling atmosphere and identify a suspect for the water loss.
What the team discovered was that a molecule called HCO+ – made up of a hydrogen atom, a carbon atom and an oxygen atom – high in Venus’ atmosphere may have been responsible for delivering the last of the planet’s water into space.
“For an analogy, let’s say I dumped the water in my water bottle,” Cangi said. “There would be a few drops left.”
HCO+ could essentially remove these droplets from Venus’ atmosphere. The same team has previously suggested that HCO+ was also the culprit causing Mars, Earth’s other neighbor, to lose its water.
The researchers say that HCO+ is constantly produced in Venus’ atmosphere, but these ions do not survive long. An ion is a positively or negatively charged molecule, which has earned its charge by either lacking some electrons needed to balance the positive charge of its protons, or by having extra electrons to provide a net negative charge in the molecule.
HCO+ lacks the electrons needed to balance the positive charge of the molecule’s protons, and is thus positively charged (hence the + symbol).
Electrons in Venus’ atmosphere quickly recombine with HCO+, splitting the molecule in two. From there, the team claims the hydrogen atoms fly away and possibly even escape into space. Hydrogen atoms make up two of the components of the water molecule (H2O), which is composed of two hydrogen atoms and one oxygen atom, so this robs Venus of the key ingredients of water.
The team thinks that before Venus reached its extremely dry state, the planet must have had an excess of HCO+ molecules in its atmosphere.
“One of the surprising conclusions of this work is that HCO+ should actually be one of the most abundant ions in Venus’ atmosphere,” Chaffin said.
However, there is a major stumbling block in this conclusion. So far we have never seen HCO+ in the atmosphere of Venus.
However, Chaffin and Cangi don’t think this is because the molecule isn’t there, but rather because humanity didn’t have the tools needed to see it. While neighbor Mars has been visited by many Earth spacecraft, few missions have been to our other neighbor Venus – and none of these had the right equipment to see HCO+.
Related stories:
– Living on Venus? Intriguing molecule of phosphine spotted again in planet’s clouds
– If Venus had Earth-like plate tectonics in its distant past, did it also have life?
– The Magellanic Clouds should be given a new name, astronomers say
But a number of future space missions are setting their sights on Venus. NASA’s Deep Atmosphere Venus Investigation of Noble Gases, Chemistry and Imaging (DAVINCI) mission is a particularly important mission. Set to launch in 2029, DAVINCI will drop a probe through Venus’ scorching atmosphere to determine the world’s chemical composition.
However, even DAVINCI will not have the right equipment to detect HCO+.
Still, the team hopes that DAVINCI (and the European Space Agency’s upcoming EnVision mission) will spark widespread interest in Venus, eventually leading to a space mission that is indeed capable of detecting HCO+, closing the story of the water loss becomes more truthful. .
“There haven’t been many missions to Venus,” Cangi concluded. “But newly planned missions will leverage decades of collective experience and a blossoming interest in Venus to explore the extremes of planetary atmospheres, evolution and habitability.”
The team’s research was published Monday (May 6) in the journal Nature.